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Tillage and Cover Cropping Effects on Aggregate-Protected Carbon in Cotton and Tomato
Soil Science Society of America Journal
Abstract
Conservation tillage (CT) and cover cropping (CC) are agricultural practices that may provide solu- tions to address water and air quality issues arising from intensive agricultural practices. This study investigated how CT and CC affect soil organic matter dynamics in a cotton(Gossypium hirsutum L.)-tomato (Lycopersicon esculentum Mill.) rotation in California's San Joaquin Valley. There were four treatments: conservation tillage, no cover crop (CTNO); conservation tillage with cover crop (CTCC); standard tillage, no cover crop (STNO); and standard tillage with cover crop (STCC). After 5 yr, the top 30 cm of soil in CTCC had an increase of 4500 kg C ha−1, compared with an increase of 3800 kg C ha−1 in STCC from initial soil C content in 1999. To enhance our understanding of C dynamics in CT systems, we pulse-labeled cotton with 13CO2 in the fi eld and followed the decomposition of both the roots and the shoots through three physical fractions: light fraction (LF), which tends to turnover quickly, and two relatively stable C pools—intraaggregate LF (iLF) and mineral-associated carbon (mC). Soil under CT treatments retained more of the cotton- residue-derived C in LF and iLF than ST 3 mo after placement in the fi eld. These differences disap- peared after 1 yr, however, with no discernable differences between CT and ST regardless of CC. In California's Mediterranean climate, CT alone does not accumulate or stabilize more C than ST in tomato-cotton rotations, and the addition of cover crop biomass is more important than tillage reduction for total soil C accumulation. Abbreviations: CT, conservation tillage; CTCC, conservation tillage with cover crop; CTNO, conservation tillage, no cover crop; iLF, intraaggregate light fraction; LF, light fraction; mC, mineral- associated carbon; SOM, soil organic matter; ST, standard tillage; STCC, standard tillage with cover crop; STNO, standard tillage, no cover crop.
... However, it is increasingly recognized that eliminating tillage entirely may not be optimal or practical in all cropping systems and soil conditions. Some degree of strategic tillage may provide benefits by disrupting compacted layers, incorporating amendments, managing heavy residue loads, and creating seedbeds for adequate plant stands [3,4]. The goal of strategic tillage is to balance the need for tillage with the need to protect soil health in a planned, precision approach. ...
... Strategic tillage can be defined as the targeted, occasional use of tillage implements in specifically defined locations, depths, and times to address priority limiting factors while minimizing disturbance of the soil [4,5]. Unlike routine conventional tillage over entire fields, strategic tillage is applied only where evidence indicates it is necessary. ...
... Multiple studies have now documented that strategic tillage systems can provide equivalent or greater crop yields compared to conventionally tilled soils, while building soil health and retaining many of the environmental advantages of no-till systems [3,4,6]. Importantly, the benefits of strategic tillage may be most pronounced in certain soil types and cropping systems. ...
Excessive conventional tillage can degrade important aspects of soil quality and health over time. Strategic tillage offers a focused solution to address priority soil limitations with minimal disturbance. This chapter reviews the current science on how strategic tillage affects key soil physical, chemical, and biological factors relevant to soil function and crop yields. In contrast, strategic tillage involves the targeted, occasional, and shallow use of tillage equipment to address specific observed soil constraints without general field disruption. Potential advantages of strategic tillage discussed include improved soil structure, increased infiltration and rooting depth, better incorporation of amendments, disruption of compaction, enhanced soil biological activity and carbon storage, increased nutrient availability, and improved crop yields. To minimize disturbance and maintain soil function, strategic tillage should be integrated with other conservation practices like cover crops and crop rotation. Criteria for selecting appropriate tillage equipment and practices based on crop, soil, and climate factors are explored. Ongoing site-specific evaluation and refinement of strategic tillage practices using crop yields and soil analysis is emphasized. Despite needing more research, strategic tillage shows promise as a precise soil management approach that maximizes productivity and resilience while balancing periodic focused tillage with principles of soil health.
... Irrigation costs were $183.59/ha Relative to fall fallow, the inclusion of a cover crop in cotton production systems typically has no effect or slightly increases bulk density, regardless of cover crop species evaluated, tillage system employed, or time since transitioning from a fall fallow system (Balkcom et al., 2013;Locke et al., 2013Locke et al., , 2015Mbuthia et al., 2015;Nouri et al., 2019;Raper et al., 2000;Sainju et al., 2005Sainju et al., , 2006Sainju et al., , 2008Sainju et al., , 2010Schwab et al., 2002;Veenstra et al., 2007). Several cover crop species have been evaluated for impact on bulk density in cotton production systems including rye, wheat, and vetch (Vicia sp.) mixtures. ...
... Several cover crop species have been evaluated for impact on bulk density in cotton production systems including rye, wheat, and vetch (Vicia sp.) mixtures. Utilization of cover crops increased soil bulk density 14% in a clay loam managed under conservation tillage (Veenstra et al., 2007). However, under standard tillage practices, utilization of cover crops had no effect on bulk density at depths of 0 cm to 15 cm. ...
... While Haruna and Nkongolo (2015) observed a 3.5% decrease in soil bulk density from cereal rye cover crops vs non-cover cropped plots in corn/soybean rotation systems, we can find no other reports of a cover crop decreasing bulk density in cotton production systems. The effect of cover crops on bulk density has been evaluated in several conventional (Nouri et al., 2019;Sainju et al., 2008Sainju et al., , 2010Veenstra et al., 2007) and reduced tillage systems (Locke et al., 2013(Locke et al., , 2015 including ridged and non-ridged soils with or without deep tillage (Balkcom et al., 2013), fall or spring para tillage (Balkcom et al., 2013;Schwab et al., 2002), chisel tillage (Sainju et al., 2005(Sainju et al., , 2006, mulch tillage (Sainju et al., 2008(Sainju et al., , 2010, strip tillage (Balkcom et al., 2013;Sainju et al., 2005Sainju et al., , 2006Schwab et al., 2002;Veenstra et al., 2007), and no-tillage (Balkcom et Table 3 Sainju et al., 2005Sainju et al., , 2006Sainju et al., , 2008Sainju et al., , 2010. Within a given tillage system, the inclusion of a cover crop in a cotton production system never improved bulk density, even when evaluated 34 years after transitioning from fall fallow (Mbuthia et al., 2015;Nouri et al., 2019). ...
Poor soil health purportedly limits crop yield and on-farm profitability in environments with a history of intensive tillage. Research was conducted to determine if cover cropping improves basic soil physical properties, crop productivity, and economic parameters in conventionally tilled soils. The effects of irrigation and cover crop species on bulk density, water infiltration rate, cotton yield, and net returns were evaluated on a Dundee silty clay loam (Fine-silty, mixed, active, thermic type Typic Endoqualfs) near Tribbett, MS in 2017 and a Leeper silty clay loam (fine, smectitic, nonacid, thermic Vertic Epiaquepts) near Starkville, MS from 2017 through 2018. Relative to the fallow production system, cereal rye and crimson clover decreased bulk density 4.6% but had no effect on water infiltration rate. Pooled over year and location, cover crop had no effect on lint yield in either irrigated or non-irrigated environments. However, transitioning from conventional to a cover crop system reduced net returns for cotton 307.87/ha on average. Our data indicate that while transitioning from a conventional to a fall cover crop production system, modest improvements in some soil physical properties due to cover crop establishment will not increase cotton productivity but will decrease net returns.
... Los residuos con mayor proporción de C estructural, presentan una relación C:N más elevada (Ruffo & Bollero, 2003) y su tasa de descomposición es inversamente proporcional a aquélla (Sánchez et al., 1996;Mulvaney et al., 2010;Sá Pereira et al., 2017). Esto incide sobre la duración del proceso y la persistencia de los residuos (Mulvaney et al., 2010), la dinámica de la MO y del N mineralizable (Veenstra et al., 2007;Restovich et al., 2011) y la disponibilidad de N para el cultivo siguiente (Mulvaney et al., 2010). Por otro lado, los residuos enterrados se descomponen más rápidamente debido a un contacto más íntimo con el suelo, lo que estimula la actividad microbiana sobre ellos (Sánchez et al., 1996;Mulvaney et al., 2010). ...
... Por otro lado, los residuos enterrados se descomponen más rápidamente debido a un contacto más íntimo con el suelo, lo que estimula la actividad microbiana sobre ellos (Sánchez et al., 1996;Mulvaney et al., 2010). El manejo de la posición de los residuos a través de la labranza también afecta la dinámica de la materia orgánica (MO) y sus fracciones, y el N mineralizable y el disponible (Veenstra et al., 2007;Domínguez et al., 2009;Mulvaney et al., 2010;Studdert et al., 2017). ...
... et al., 2004). Así, los beneficios de la inclusión de CPV en los sistemas de cultivo sobre la MO edáfica se manifestarían más rápidamente bajo labranza conservacionista, debido a que tienden a reducir la tasa de descomposición de residuos (Veenstra et al., 2007;Blanco Canqui et al., 2015) (tratamientos con residuos en superficie, Figura 1). En este estudio, los tratamientos con residuos enterrados presentaron un 6% menos de COT, pero un 16% menos de COP que aquéllos con los residuos en superficie (Tabla 1). ...
Los cultivos puente verde (CPV) inciden sobre el suelo y el cultivo posterior según su tipo y cómo se descomponen sus residuos. Se hipotetizó que 1) los residuos de CPV gramíneas se descomponen a menor tasa que los de leguminosas; 2) la descomposición de CPV leguminosas genera mayor y más rápida disponibilidad de nitrógeno (N); y 3) las fracciones orgánicas lábiles del suelo aumentan más y más tarde con CPV gramíneas y con los residuos en superficie. Se realizó un experimento sobre un Argiudol típico con CPV avena (Avena sativa L.), vicia (Vicia villosa Roth.) y un testigo sin CPV (TE). Se colocaron iguales cantidades de residuos picados de ambos CPV en superficie y enterrados. Se tomaron muestras de 0-20 cm en 7 momentos en 133 d para determinar: carbono (C) remanente de residuos (CR), C orgánico total (COT) y particulado (COP), N de amonio liberado en anaerobiosis (NAN) y N de nitrato (N-NO3 -). El CR de los residuos enterrados disminuyó a mayor tasa y sin diferencia entre avena y vicia. En superficie, la vicia se descompuso más rápido que la avena y a los 133 d se había descompuesto 60 y 79% de sus residuos, respectivamente. COT y COP fueron mayores luego de avena (75,1 y 18,6 Mg ha-1, respectivamente) que luego de vicia y TE (70,4 y 16,8 Mg ha-1, respectivamente). También fueron menores con los residuos enterrados (69,7 y 15,9 Mg ha-1, respectivamente) que cuando quedaron en superficie (73,3 y 18,9 Mg ha-1, respectivamente). La posición de los residuos no afectó el NAN, pero fue mayor luego de avena y vicia (63,1 mg kg-1) que del TE (50,2 mg kg-1). COT, COP y NAN mostraron escasa variación durante el ensayo. Hasta los 49 d, el N-NO3 - aumentó (45 a 108 kg ha-1) y fue mayor cuando el CPV fue vicia. No se reunieron evidencias suficientes para rechazar la primera y segunda hipótesis, pero sí para rechazar la tercera.
... De Gryze et al. (2009) conservation tillage 3 locations in California; 3-yr study 0.33 Veenstra et al. (2007) conservation tillage Longest-running study in California, but only 5 yrs 0.00 Source: Calculated from source to common units; cropland area, if needed for national calculation and not in given reference, is from U.S. agricultural census. ...
... In drier regions, it is also necessary to consider the net benefit of cover crops if irrigation is necessary for their inclusion. Adding winter cover crops can result in soil C increases of more than 3 t CO 2 e ha -1 yr -1 (De Gryze et al. 2009;Sainju et al. 2002;Veenstra et al. 2007), with the highest rates in warmer-winter locations such as California and Georgia. Despite these favorable results, as of 1995, cover crops were used on only 4% of the major field crop area . ...
... Cover cropping and increased grain rotations in potato-grain crop systems on sandy loam soil increased soil C content and reduced erosion (Al-Sheikh et al. 2005), and cover cropping and no-till showed increased soil C in California vineyards (Steenwerth and Belina 2008). In contrast, while cover cropping in a Mediterranean tomato-cotton rotation in California increased soil carbon, no-till did not (Veenstra et al. 2007); and in a tomato system in Georgia, no-till only increased soil C when combined with cover crop and N fertilization (Sainju et al. 2002). Compost substitution for synthetic fertilizer also has potential, as shown in a maize-vegetable-wheat rotation in Pennsylvania where compost increased soil carbon by 16%-27% over 9 years compared to a decline with synthetic fertilizer (Hepperly et al. 2009). ...
... By contrast, P and K concentrations (g/kg) increased over the same period, but the differences between the control and treatment were not significant. These results may be important to a grower who, for example, grows in a soil of low fertility and cation exchange capacity, and/or where the use of cover crops is eschewed (Álvaro-Fuentes et al., 2008;Steenwerth and Belina, 2008;Veenstra et al., 2007). a Collective values averaged for both Shiraz and Semillon blocks per treatment where n = 6 and n =12 per sub block respectively. ...
... These variances could be accounted for by differences in crop PVB production through differences in soil type and quality and changing climate conditions (Celette et al., 2009;Coll et al., 2009;Salomé et al., 2016). In addition, various studies report a positive enhancement of C cycles in semi-arid/ Mediterranean environments when cultivation is minimised and cover crops are properly managed (Álvaro-Fuentes et al., 2008;Steenwerth and Belina, 2008;Veenstra et al., 2007). ...
The wine industry worldwide faces increasing challenges to achieve sustainable levels of carbon emission mitigation. This study seeks to establish the feasibility of harvesting winter pruned vineyard biomass (PVB) for potential use in carbon footprint reduction as a renewable biofuel for energy production. Of particular interest is the role PVB plays as a carbon source in vineyard soils and what effect annual removal might have on soil carbon. An investigation was carried out in the Coombe vineyard, Waite Campus (University of Adelaide), Australia. Vines are grown in a Vertic clay loam soil with well-managed mid-row swards in a temperate zone. A comparison was undertaken of two mid-row treatments after 13 years of consistent management: 1) the deliberate exclusion of PVB from every third row, and 2) in the remaining rows PVB was incorporated at an average of 3.4 and 5.5 t/ha in two 0.25 ha blocks containing Shiraz and Semillon respectively. In both 0-10 cm and 10-30 cm soil core sample depths, combined soil carbon % values in the desired range of 1.80 to 3.50 were not significantly different between treatments or cultivars and yielded an estimated 42 t/ha of soil carbon. Other key physical and chemical values were likewise not significantly different between treatments. Results suggest that in a temperate zone vineyard, managed such as the one used in this study, there is no long-term negative impact on soil carbon sequestration through removing PVB. This implies that growers could confidently harvest PVB for use in biofuel production.
... Catch crops increase the carbon sequestration potential of agroecosystems [32]. Under optimal conditions, the biomass of catch crops can accumulate up to 4.4-5.6 ...
... The change in soil C, insignificant or slight, in a short time, is significant after several years of cultivation. According to Veenstra et al. [32], in the cultivation of tomatoes, using CCs allowed for 1.8-2.3 Mg C ha −1 year −1 . ...
Sulfur (S) directly influences the proper development, yield, and biological value of Allium sativum. The sulfuric forms of S are easily leached from the soil due to poor sorption. In this context, we looked at to what extent application of S and biomass of catch crops (CCs) left until spring would cause an increase in the yield; we also looked at the macro- and micronutrient content of garlic plants. The experimental factors included applications of 0 and 20 kg ha⁻¹ S to CCs consisting of Trifolium alexandrinum, Raphamus sativus var. oleiformis, Fagopyrum esculentum, Sinapis alba, and control. The bulbs contained more dry matter and macro- and micronutrients (N, P, K, S, Zn, and Fe) than those without S. Garlic plants cultivated with S accumulated more glutathione and total phenolic acids (TPA), and the extracts showed greater antioxidant activity (AA) than those cultivated without S. In 2019 and 2020, the cultivation of winter garlic with S, in combination with clover contributed to an increase in the content of dry matter, S, TPA, AA in bulbs. In the cultivation with fodder radish garlic plants accumulated more nitrogen (N), S, TPA, AA and glutathione in bulbs. In those cultivated with buckwheat, garlic contained more TPA, AA, glutathione, and with mustard more TPA and AA. However, further research is needed to select the species of CC and to determine the S dose to be applied in the effective biofortification of garlic in a sustainable agriculture system.
... The principles of regenerative agriculture are similar to those of conservation agriculture and consist of minimizing soil disturbance, eliminating or reducing agrichemical use, eliminating spatio-temporal bare soil events, maximizing plant diversity, and integrating livestock into a cropping operation (Rodale, 1983;Rhodes, 2017;LaCanne and Lundgren, 2018;Gosnell et al., 2019;Pecenka and Lundgren, 2019;Fenster et al., 2021). These regenerative practices increase organic matter in the soil, which is an active area of research for soil health and climate mitigation efforts (Veenstra et al., 2007;Ryals and Silver, 2013;Demestihas et al., 2017;LaCanne and Lundgren, 2018;Soto et al., 2021). Agriculture is an important cause for reductions in biodiversity (Kovács-Hostyánszki et al., 2017;Sanchez-Bayo and Wyckhuys, 2019;Stewart et al., 2019), and regenerative practices that enhance soil C, such as maintaining permanent ground cover, can help to promote biodiversity (Lundgren et al., 2006;Eilers and Klein, 2009;Klein et al., 2012;Vukicevich et al., 2016Vukicevich et al., , 2019Demestihas et al., 2017;Kovács-Hostyánszki et al., 2017;LaCanne and Lundgren, 2018). ...
... For example, regenerative maize and cattle grazing systems in the Midwest have significantly better soil health metrics, improved biodiversity, and reduced pest damage, while being twice as profitable relative to conventional systems (LaCanne and Lundgren, 2018;Pecenka and Lundgren, 2019). Additionally, research in tomato fields in California's Central Valley showed that tomato-cotton rotations that integrated cover cropping and conservation tillage led to higher levels of soil carbon than either practice on its own (Veenstra et al., 2007). Research comparing rain fed regenerative and conventional almond (Prunus dulcis) orchards in Spain found that regenerative management can improve soil quality and ecosystem services, particularly in systems that stack regenerative practices (Soto et al., 2021). ...
Regenerative agriculture aims to improve soil health and promote biodiversity while producing nutritious food profitably. Almonds are the dominant crop in California agriculture in terms of acreage and revenue generated. We examined the soil health, biodiversity, yield, and profit of regenerative and conventional almond production systems that represented farmer-derived best management practices. Regenerative practices included abandoning some or all synthetic agrichemicals, planting perennial ground covers, integrating livestock, maintaining non-crop habitat, and using composts and compost teas. Total soil carbon (TSC), soil organic matter (SOM), total soil nitrogen (TSN), total soil phosphorous, calcium, sulfur, and soil health test scores were all significantly greater in regenerative soils. Water infiltrated regenerative soils six-fold faster than conventional soils. Total microbial biomass, total bacterial biomass, Gram+ bacteria, and Actinobacteria were significantly greater in regenerative soils. There was more plant biomass, species diversity, and percent cover in regenerative orchards. Invertebrate richness and diversity, and earthworm abundance and biomass were significantly greater in regenerative orchards. Pest populations, yields, and nutrient density of the almonds were similar in the two systems. Profit was twice as high in the regenerative orchards relative to their conventional counterparts. No one practice was responsible for the success of regenerative farms; their success was the result of simultaneously combining multiple regenerative practices into a single, functional farm system. This style of farming may assist in combatting planetary scale problems (e.g., climate change, biodiversity loss, agricultural pollution, chronic human health problems, and declining rural communities) while making farms more profitable and resilient.
... They deposit organic C into soil, providing potential offsets for N 2 O emissions. For example, after five years of cover crops in a tomato/cotton rotation, Veenstra et al. [136] reported that soil organic C (SOC) content increased in the top 30 cm soil by 4.0 to 4.9 Mg C ha −1 compared to the absence of cover crops. Mitchell et al. [137] also observed that cover crops sequestered 0.46 to 0.63 Mg C ha −1 yr −1 more SOC than no cover crops. ...
... Mitchell et al. [137] also observed that cover crops sequestered 0.46 to 0.63 Mg C ha −1 yr −1 more SOC than no cover crops. Using the soil C sequestration rate of 2.94 Mg CO 2 ha −1 yr −1 in tomatoes under cover crops [136], the global warming potential of adopting a cover crop practice is −285 Gg CO 2 eq when SDI and standard tillage practices are adopted and −242 Gg CO 2 eq when furrow irrigation and standard tillage practices are adopted. In other words, cover crops have the potential to decrease GHGs by −327 CO 2 eq yr −1 to −370 CO 2 eq yr −1 compare with standard practices. ...
Greenhouse gas (GHG) emissions from arid irrigated agricultural soil in California have been predicted to represent 8% of the state’s total GHG emissions. Although specialty crops compose the majority of the state’s crops in both economic value and land area, the portion of GHG emissions contributed by them is still highly uncertain. Current and emerging soil management practices affect the mitigation of those emissions. Herein, we review the scientific literature on the impact of soil management practices in California specialty crop systems on GHG nitrous oxide emissions. As such studies from most major specialty crop systems in California are limited, we focus on two annual and two perennial crops with the most data from the state: tomato, lettuce, wine grapes and almond. Nitrous oxide emission factors were developed and compared to Intergovernmental Panel on Climate Change (IPCC) emission factors, and state-wide emissions for these four crops were calculated for specific soil management practices. Dependent on crop systems and specific management practices, the emission factors developed in this study were either higher, lower or comparable to IPCC emission factors. Uncertainties caused by low gas sampling frequency in these studies were identified and discussed. These uncertainties can be remediated by robust and standardized estimates of nitrous oxide emissions from changes in soil management practices in California specialty crop systems. Promising practices to reduce nitrous oxide emissions and meet crop production goals, pertinent gaps in knowledge on this topic and limitations of this approach are discussed.
... Annual precipitation is about 180 mm. The soil is classified as Panoche clay loam (fine-loamy, mixed superlative, thermic Typic Haplocambids) (Veenstra et al., 2007). A field comparison of conservation and standard tillage, with and without cover crops between the economic crops, was established in 1999 (16-year management history as of the end of 2015; Mitchell et al., 2017). ...
... A field comparison of conservation and standard tillage, with and without cover crops between the economic crops, was established in 1999 (16-year management history as of the end of 2015; Mitchell et al., 2017). The farming systems in this experiment are described in detail elsewhere (Veenstra et al., 2007). The only soil disturbance operations in the conservation tillage systems were shallow cultivation during establishment of a tomato (Solanum lycopersicum L.) crop, used as the economic crop, during the first eight years of the experiment. ...
... At the time the NRI-CA Project was started, NT practices were used on less than 2% of annual crop acreage and 0% of cotton acreage in the SJV and informal estimates of the extent of cover cropping were on a similar level. Since 1999, the project consistently has implemented cover crop and tillage system comparisons that differ substantially in terms of soil disturbance intensity and C inputs via cover crops (Mitchell et al., , 2008(Mitchell et al., , 2009aVeenstra et al., 2007). Various aspects and findings of the early stages of this long-term study have been reported previously including impacts of NT on soil C and nitrogen (N) (Veenstra et al., 2006(Veenstra et al., , 2007, dust emissions (Baker et al., 2005), economics (Mitchell et al., 2009a) and cover crop inputs . ...
... Since 1999, the project consistently has implemented cover crop and tillage system comparisons that differ substantially in terms of soil disturbance intensity and C inputs via cover crops (Mitchell et al., , 2008(Mitchell et al., , 2009aVeenstra et al., 2007). Various aspects and findings of the early stages of this long-term study have been reported previously including impacts of NT on soil C and nitrogen (N) (Veenstra et al., 2006(Veenstra et al., , 2007, dust emissions (Baker et al., 2005), economics (Mitchell et al., 2009a) and cover crop inputs . ...
Despite approximately 45% of U.S. cotton being produced using no-tillage (NT) or strip-tillage, these seeding techniques are not yet being used commercially in California. From 2010 to 2013, we compared cotton production under NT versus standard tillage (ST) practices with a winter cover crop (CC) or without (NO) cover crops in Five Points, CA. Tractor trips across the field were reduced by 40% in the NT systems relative to the ST approaches. Residue cover was 93, 83, and 2% for the NTCC, NTNO, and the ST systems, respectively. Average lint yields combined over the four years of this study were similar between ST and NT (1481.4 vs 1484.7 kg ha-1), however, the average yield with NO was higher than with CC (1526.1 vs 1440.0 kg ha-1). There was a tillage X cover crop interaction in 2011 with a yield difference between CC and NO within ST, but not NT. There were no differences between the STNO and NTNO systems across the four years. As long as yields can be maintained, externalities such as shifts in irrigation systems away from surface to drip and overhead irrigation, as well as continued water shortages could warrant the learning curve effort and the retooling that will be required to scale up the conversion from traditional tillage cotton production to NT in this region.
... At the time the National Research Initiative Project was started, CT practices were used on less than 2% of annual crop acreage in the CV ( Mitchell et al. 2007), and informal estimates of the extent of cover cropping were on a similar level. Since 1999, the project has consistently implemented cover crop and tillage system comparisons that differ in terms of soil disturbance inten- sity and organic matter inputs ( Mitchell et al. 2008aMitchell et al. , 2009Veenstra et al. 2007). Various aspects and findings of the early stages of this long-term study have been previously reported including impacts of CT on soil C and N ( Veenstra et al. 2006Veenstra et al. , 2007Mitchell et al. 2009), dust emissions ( Baker et al. 2005), and economics ( Mitchell et al. 2009). ...
... Since 1999, the project has consistently implemented cover crop and tillage system comparisons that differ in terms of soil disturbance inten- sity and organic matter inputs ( Mitchell et al. 2008aMitchell et al. , 2009Veenstra et al. 2007). Various aspects and findings of the early stages of this long-term study have been previously reported including impacts of CT on soil C and N ( Veenstra et al. 2006Veenstra et al. , 2007Mitchell et al. 2009), dust emissions ( Baker et al. 2005), and economics ( Mitchell et al. 2009). In this paper we add information on the biomass production of the cover crop systems and soil water balance from 1999 through 2014. ...
Cover crops are currently not widely used in annual crop production systems in California's semiarid Central Valley due to concerns about lost opportunity costs and uncertainties about water use. From 1999 through 2014, we quantified cover crop biomass production for a variety of mixtures under winter precipitation and limited supplemental irrigation. In a separate study, we also determined changes in soil water storage under three cover crop mixtures compared to fallowed plots during two (2013 and 2014) winter periods to investigate tradeoffs associated with water use by cover crops in this region. Over the 15 years of the project that were characterized by recurring drought, a total of 22.8 Mg ha-1 (20,360 lb ac-1) of aboveground cover crop biomass was produced with a total precipitation of 209 and 20 cm (82 and 8 in) of supplemental irrigation applied in 1999, 2012, and 2014. Cover crop biomass varied from 0.39 Mg ha-1 (348 lb ac-1) in the low precipitation period (winter of 2006 to 2007) to 9.34 Mg ha-1 (8,340 lb ac-1; winter of 2000 to 2001). Soil water storage in the sampled depth (0 to 90 cm [0 to 35 in]) for the fallow and each of the cover crop mixtures was compared each year from January to March, the primary growing period for cover crops in this region. Net soil water storage increased during this period by 4.8 and 4.3 cm (1.9 and 1.7 in) in 2013 and 2014, respectively, for the fallow system, but in the cover crop mixture plots, there was no additional water storage. Instead, water use by the cover crop mixes resulted in a negative water balance over the cover crop growth period on an average of 0.47 and 0.26 cm (0.19 and 0.10 in) in 2013 and 2014, respectively. Thus, compared to the fallow system, cover crops depleted 5.3 and 0.67 cm (2.1 and 0.26 in) and more water from the 0 to 90 cm (0 to 35 in) profile in 2013 and 2014, respectively. From this long-term systems research, we conclude that while vigorous growth of winter cover crops in the Central Valley of California may not be possible in all years due to low and erratic precipitation patterns, there may be benefits in terms of providing ground cover, residue, and photosynthetic energy capture in many years. However, cover crop biomass production may come at a cost of soil water depletion in this semiarid, drought-prone region.
... In general, cover cropping is well known to provide benefits to the soil through the reduction of erosion, reduction of nutrient loss through runoff and leaching, and contribution to SOC stores (Kaspar & Singer, 2011). Veenstra et al. (2007) reported that cover cropping practices increased both organic carbon and the labile pool of carbon. CC has shown positive response to SOC (Abdalla et al., 2019;King & Blesh, 2018). ...
Agricultural practices alter the organic carbon dynamics in soil. An experiment was conducted to study the effect of carbon amendments, tillage, and cover cropping on permanganate oxidizable carbon (POXC), total organic carbon (TOC), and wet aggregate stability (WAS) in a 2‐year crop sequence (corn–cover crop–cotton–cover crop) at the Texas A&M Research Farm. Two carbon amendments (biochar and composted biosolid) were applied at the rate of 500 kg C ha⁻¹, along with a control. Two tillage practices were evaluated: conventional tillage (CT) and no‐tillage (No‐Till). A cover crop (CC) mixture of oat, mustard, and pea and no cover crop (No‐CC) were also evaluated. Treatments were arranged in a split‐split plot design with four replications. Amending the soil with carbon as composted biosolid or biochar affected POXC at both the 0‐ to 5‐ and 5‐ to 15‐cm depths. The POXC was significantly higher for the biochar treated plots for corn and CC after corn but significantly lower POXC was observed after cotton with biochar‐treated plots. The POXC increased under No‐Till compared with CT and CC plots relative to No‐CC plots. The TOC was not sensitive to soil management practices. The POXC and TOC both decreased with depth. The WAS greater under No‐Till and CC plots. The POXC and WAS were influenced by soil management practices and can be useful indicators to assess short‐term soil health improvements. The POXC and WAS were positively related, suggesting that one may be used to predict the other.
... Replacing PT (inversion ploughing tillage) with CT contributes to the accumulation of carbon and nutrients in the near-surface soil layers after 5-8 years (Abdollahi & Munkholm, 2014;Shao et al., 2016). In the short term (1-5 years), an increase in SOC is not usually accompanied by an improvement in soil chemical properties, such as total nitrogen, available phosphorous, exchangeable calcium and magnesium (Cooper et al., 2020;Haruna & Nkongolo, 2019;Sokolowski et al., 2020;Veenstra et al., 2007). Long-term experiments mainly focus on total nitrogen, and limited data are available on the concentration of other elements (Kopittke et al., 2016). ...
Conservation tillage (CT) is a ploughless tillage with a reduced number of operations, and its positive effect on soil functions and health is widely known. Multivariate analyses are required to choose indicators that adequately characterize the changes in soil health. However, there is little research on the comprehensive analysis of the full spectrum of soil physical, chemical and biological properties. Therefore, we examined 21 soil parameters in a long-term CT experiment conducted in Hungary. Four pairs of similarly sized CT and conventional ploughing tillage (PT) plots were set up in 2003 on Luvisols. The soil samples were collected after 17 years. The total organic carbon (TOC) increased significantly in the 0–15 cm layer at CT sites compared to those in PT, indicating a total increase of 5.22 t ha−1 TOC stock. In addition, the increasing biological activity and improved soil structure were the most important processes at the CT sites. Furthermore, more complex humic substances with higher molecular weights are characteristic of water-extractable organic matter (WEOM) as a result of CT. The potentially available nitrogen, phosphorus and potassium were also measured with a relatively high response ratio. Slowly changing parameters, such as cation exchange capacity and base saturation, are important soil physical and chemical parameters, but are not good indicators of the impact of tillage practices. Based on principal component analysis, we suggest the use of water-extractable organic C, amino-nitrogen, water-stable aggregates, available P and K and photometric analysis of WEOM to identify the soil improving processes.
... Another 5-year research in California revealed similar results, with no substantial increase in soil C in conservation tillage over normal tillage in the top 0 to 30 cm. The results were positive only in the cover croppingbased treatments (Veenstra et al. 2007). In another study reported by Sainju et al. (2006), cereal + legume-based cover cropping (rye + vetch) enhances the SOC compared with non-cover cropping under different tillage practices ( Figure 5). ...
Climate change and greenhouse gas emissions (GHGs) are critical environmental issues of the 21st century. The increase in atmospheric GHGs concentration since the Industrial era induced interest in identifying practices to reduce these gases and soil C sequestration could be the best solution for reducing CO2 enrichment of the atmosphere. However, the C sequestration capacity of soils is influenced by various management technologies like reduced tillage, organic amendments, cover cropping, nutrient management and biochar. A significant amount of SOC could be sequestered by farm yard manure (FYM) application which enhances lignin and lignin-like molecules that are crucial components of resistant C pools. Legume-based crop rotation promotes C sequestration by accumulating C in macro-aggregates. Biochar causes a positive effect on soil aggregation and SOC storage through the release of multivalent ions. C sequestration depends profoundly on stabilizing the added C through appropriate management practices. The C stabilization mechanism can be better understood following the fractionation of C in different pools. The recalcitrant C pools stored in micro-aggregates represent C sequestration, while C stored in macro-aggregates is C accumulation and a short-term concept. Therefore, this review aims to identify the best management practices leading to C build-up, besides improving C stabilization by imparting recalcitrance to SOC.
... Second, conservation agriculture supports the development of healthy soils. For example, several studies have shown that reduced disturbance tillage systems sequester more carbon and decrease greenhouse gas emission (Reicosky and Allmaras, 2003;Palm et al., 2014;Sanz-Cobena et al., 2017); improve soil physical properties such as soil bulk density and penetration resistance (Veenstra et al., 2006(Veenstra et al., , 2007; increase microbial biomass, richness, and activity (Zuber and Villamil, 2016;Martens, 2001;Johnson and Hoyt, 1999); and reduce dust and air particle pollution (Baker et al., 2005;Madden et al., 2008;Reicosky and Allmaras, 2003). While some studies show that reduced disturbance tillage reduced yield (Pittelkow et al., 2015), others have found that the yield is unaffected (Naab et al., 2017;Rasmussen, 1999;Alvarez and Steinbach, 2009) while reducing cost (Upadhyaya et al., 2001;Mitchell et al., 2009;González-Sánchez et al., 2016). ...
We studied the long-term impact of contrasting tillage and cover cropping systems on soil structure and hydraulic properties. Complete water retention and conductivity curves for the top (0–5 cm) and subsurface (20–25 cm) soils were characterized and contrasted. Dynamic water storage and retention were evaluated using numerical simulations in HYDRUS-2D software. Compared with standard-till (ST) and no-cover-crop (NO) systems, soils under no-till (NT) and cover cropping (CC) systems showed improved soil structure in terms of pore size distribution (PSD). Changes in hydraulic conductivity (K) under these systems led to an increased infiltration rate and water retention. However, NT and CC plots had lower water content at field capacity (33 kPa suction) and lower plant-available water (PAW) compared with ST and NO plots. Numerical simulations, however, showed that NT and CC plots have higher water storage (albeit marginal in magnitude) and water availability following irrigation. Because the numerical simulations considered retention and conductivity functions simultaneously and dynamically through time, they allow the capture of hydraulic states that are arguably more relevant to crops. The study concludes that the long-term practices of NT and CC systems were beneficial in terms of changes to the PSD. NT and CC systems also marginally improved soil water conductivity and storage at the plot scale.
... This can be interpreted as short-term SOC losses resulting from the proportional increase in tillage intensity, which seem to be relatively large compared to the Great Plains and Corn Belt Regions (Eve et al. 2002). Our results agreed with other studies in a Mediterranean climate; however, studies have shown that conservation tillage does not necessarily increase SOC relative to C stocks in intensively tilled soils over time (Veenstra et al. 2007;Aguilera et al. 2013). ...
Context
Unreplicated trials are common in agriculture. However, statistical inferences differ from those of traditional experiments based on small, replicated plots.
Aims
To present a method to assess management effects on soil carbon (C) storage from unreplicated, side-by-side field trials.
Methods
Two estimates of means with spatially correlated errors are compared using a corrected t-statistic. Then causal inference is made by analysing a significant difference between the means (P < 0.05) and its changes over time. The use of the method is described in comparing yield and organic C stocks between two large fields. Yield was measured during 1997–2005 with a commercial yield monitor, and soil organic C stocks during 2003–2005. The fields experienced the same tillage practice until autumn 2003 and then with different tillage intensity.
Key results
The results show that crop C yield did not differ between the fields when using the same tillage practice but was greater in the tilled than the no-till field. The results also suggest that total and particulate organic matter-C contents depend on tillage history. For comparative purposes, the data were also analysed using standard mixed model analysis with a semivariogram model for spatial autocorrelation among the residuals. The mixed model results were generally similar to those of the corrected t-statistic method. The mixed model was often, but not always, less conservative than the corrected t-statistic model.
Conclusions
The method allows analysis of whole-field data and improves our understanding of soil C processes in commercial fields, where agricultural assessment cannot involve replication due to agronomic and economic constraints.
Implications
The method complements observational data analyses and can offer a direction towards whole-field management.
... For example, reduced disturbance tillage systems have been shown to sequester carbon and decrease greenhouse gas emission (Reicosky and Allmaras, 2003;Palm et al., 2014;Sanz-Cobena et al., 2017); increase soil fertility (Veenstra et al., 2006(Veenstra et al., , 2007; 45 increase microbial biomass, richness, and activity (Zuber and Villamil, 2016;Martens, 2004;Johnson and Hoyt, 1999); and improve environmental quality (Baker et al., 2005;Madden et al., 2008;Reicosky and Allmaras, 2003) without compromising yield (Naab et al., 2017;Rasmussen, 1999;Alvarez and Steinbach, 2009) while reducing cost (Upadhyaya et al., 2001;Mitchell et al., 2009;González-Sánchez et al., 2016). Cover cropping-planting between cropping seasons to maintain soil coverage throughout the year and often to replenish soil N-provides many beneficial services including soil cover, residues, and 50 biological diversity (Mitchell et al., 2019). ...
Using laboratory measurements and numerical simulations, we studied the long-term impact of contrasting tillage and cover cropping systems on soil structure and soil hydraulic properties. Complete water retention and conductivity curves for top (0–5 cm) and subsurface (20–25 cm) samples were characterized and contrasted. Plot-level properties of water storage and retention were evaluated using numerical simulations in HYDRUS-2D software. Soils under no-till (NT) and cover cropping (CC) systems showed an improved soil structure in terms of pore size distribution (PSD) and the hydraulic conductivity (K) under these systems led to increased infiltration rate and water retention. The conventional measurement of water content at field capacity (water content at −33 kPa suction) and the associated plant available water (PAW) showed that NT and CC plots had lower water content at field capacity and lower PAW compared to standard-till (ST) and plots without cover crop (NO). The numerical simulations, however, showed that NT and CC plots have higher profile-level water storage (albeit marginal in magnitude) and water availability following irrigation. Because the numerical simulations consider retention and conductivity functions simultaneously and dynamically through time, they allow the capture of hydraulic properties that are arguably more relevant to crops. The changes in PSD, water conductivity, and water storage associated with NT and CC systems observed in this study suggest that these systems are beneficial to general soil health and improve water retention at the plot scale.
... Cover crops have a good adoption with cultural practice to improve soil health and crop yields [10]. Previous studies have shown that apart from providing N, winter legume cover crops can improve physical soil properties, reduce soil erosion, conserve soil water, recycle plant nutrients, and increase crop yield potential and soil productivity [36]. Using winter legume cover crops, on the other hand, is often limited by the asynchrony of cover crop planting windows and biomass accumulation with planting windows for summer cash crops [37]. ...
One of the important challenges in Maize (Zea mays L.) establishment is weed pressure control, therefore in this study we aimed at assessing whether cover crops alone can control weeds and improve maize stand establishment in reduced-tillage system and whether Maister OD herbicide treatments should be applied or not. To find out, we conducted some field experiments at the Agriculture , Natural Resources Research and Education Station in Moghan, Ardabil province in Iran in 2015-2017 using split plot design with three repli-cations. The main plots consisted of three cover crop treatments [Vetch (Vicia villosa L.), Clover (Trifolium incarnatum L.) and Fallow (No cover crop). The sub-plots were Maister OD herbicide deferments (applied 1.5 L/ha and No Herbicide) as post emergence application. Vetch and Clover provided more effective weed control than no cover crop; however, soil coverage and biomass clover was also lower in cover crops. Maize yield, however it was significantly lower in non-treated herbi-cide and no cover crops plots (7 Ton ha −1) than plots 100% herbicides with cover crops (9 Ton ha −1). The study showed that supplemental herbi-cide application is needed with using cover crops to improve Maize establishment.
... Appropriate management strategies include to reduce or eliminate soil tillage, reduce bare fallow, crop rotation procedures, crop rotation with forage plants, boost primary production, and enhance the return of organic matter to soil (Paustian et al., 1997;Follett, 2001;Hutchinson et al., 2007;Lewczuk et al., 2017). Replacement of winter intercrop fallow by cover crops (CCs) is known to decrease nitrate leaching, increase soil fertility, and improve N use efficiency (Veenstra et al., 2007;Restovich et al., 2011). ...
The increase in atmospheric GHGs can be mitigated by capturing CO2 from the atmosphere and/or by reducing their emissions. Replacing winter intercrop fallow by cover crops (CCs) can sequester carbon and improve nitrogen use efficiency under proper management. We monitored two cycles of a cash crop namely soybean (soy1) and double cropping soybean (soy2) and their respective post‐harvest periods. During the first period, a winter crop (wheat) was used as an alternative to CCs and in the second period a chemical fallow treatment (bare soil) was applied. CO2 and N2O exchange rates were estimated with turbulent flux measurements, and N2O fluxes with complementary static chambers. During the soy1 / wheat sequence, the soil gained 2800 kg C eq ha⁻¹, while during the soy2 / bare fallow sequence the soil lost 5083 kg C eq ha⁻¹. Excluding the carbon exported by harvest, both sequences lost carbon, but the soy2 / bare fallow cycle was five‐fold higher. The replacement of bare fallow by a winter cover crop like wheat decreases N2O emissions considerably and converts carbon losses (by respiration) into gains (by fixation in photosynthesis). The replacement of traditional non‐harvested cover crops by winter wheat may provide not only similar advantages in terms of soil improvement, preservation and reduction in nitrogen loss, but also an additional harvest. It will be necessary to adjust the fertilization of this cover crop to prevent excess nitrogen from accumulating in soils.
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... According to these results, and in particular the grain yield per fad the only significant interaction was that between the preceding crop and N level which clearly indicate an increase in soil fertility level, most probably from available N, where about 50 % of N level could be saved when maize was preceded by berseem than by wheat (Table 4-d). Veenstra et al. (2007) showed that, winter legume cover crops can improve physical soil properties, reduce soil erosion, conserve soil water, recycle plant nutrients, and increase crop yield potential and soil productivity. ...
Response of Yellow Maize Yield to Preceding Crop Effect and NP Fertilization Level
... Integrating legume CCs in these systems reduces the total dependence on fertilizer N and improves the environment by decreasing N losses (Reinbott et al., 2004). Winter legume CCs help improve soil physical properties, reduce soil erosion, conserve soil water, recycle nutrients and increase crop yield potential (Veenstra et al., 2007). However, the lack of favorable planting window and weather conditions means that the winter legume CCs often accumulate limited biomass. ...
Crops like corn and soybean occupy vast area in the Midwest, USA. When land is left fallow after the harvest of these crops, a number of degradation factors operate and bring about soil erosion, nutrient loss, decreased soil organic carbon, reduced biological activity and increase in weed biomass. Integrating cover crops (CCs) into this system would build benefits that the very system lacks. There are various CCs available, but leguminous CCs allows for reduced application of fertilizer nitrogen and builds the soil fixed atmospheric nitrogen. Winter CCs are restricted in the Midwest because of the short planting window which greatly minimizes the biomass accumulation. Warm season CCs would serve well here. Sunn hemp is one such tropical CC that grows well in temperate conditions too, without producing seeds. It comes with many benefits - including decreased soil erosion, improved soil organic carbon, increase in soil fixed nitrogen, higher biomass that adds organic matter and N to the soil, reduced weed density and weed biomass. The timing and method of termination influences the residue management. Going by the benefits it adds, sunn hemp is a viable warm season CC that can be grown in the Midwest and has great potential in fallows, prevented plant acres, areas of crop failure (planted and failed) and also in areas after the harvest of the short season small grains or processing crops. However, intensive research on sunn hemp is needed in the Midwest which is discussed.
... A cover crop is a transition crop between two production systems, and it has the potential to provide multiple benefits, such as preventing soil erosion, improving soil physical and biological properties, supplying nutrients, suppressing weeds, improving the availability of soil water, and breaking pest cycles. Many researchers have emphasized that cover crops increase soil organic matter, infiltration rate, and nitrogen fertilizer use efficiency (Bordovsky et al., 1999;Veenstra et al., 2007;Li et al., 2008). In contrast, several other researchers (Balkcom et al., 2007;Dabney et al., 2001) reported a potential disadvantage of reducing soil water for subsequent cash crops when growing cover crops. ...
Interest in cover crops has been increasing in the Texas Rolling Plains (TRP) region, mainly to improve soil
health. However, there are concerns that cover crops could potentially reduce soil water and thereby affect the yield of subsequent cash crops. Previous field studies from this region have demonstrated mixed results, with some showing a reduction in cash crop yield due to cover crops and others indicating no significant impact of cover crops on subsequent cotton fiber yield. The objectives of this study were to (1) evaluate the CROPGRO-Cotton and CERES-Wheat modules within the cropping system model (CSM) of the Decision Support System for Agrotechnology Transfer (DSSAT) for the TRP region, and (2) use the evaluated model to assess the long-term effects of growing winter wheat as a cover crop on water balances and seed cotton yield under irrigated and dryland conditions. The two DSSAT crop modules were calibrated using measured data on soil water and crop yield from four treatments: (1) irrigated cotton without a cover crop (CwoC-I), (2) irrigated cotton with winter wheat as a cover crop (CwC-I), (3) dryland cotton without a cover crop (CwoC-D), and (4) dryland cotton with a winter wheat cover crop (CwC-D) at the Texas A&M AgriLife Research Station at Chillicothe from 2011 to 2015. The average percent error (PE) between the CSM-CROPGRO-Cotton simulated and measured seed cotton yield was -10.1% and -1.0% during the calibration and evaluation periods, respectively, and the percent root mean square error (%RMSE) was 11.9% during calibration and 27.6% during evaluation. For simulation of aboveground biomass by the CSMCERES-Wheat model, the PE and %RMSE were 8.9% and 9.1%, respectively, during calibration and -0.9% and 21.8%, respectively, during evaluation. Results from the long-term (2001-2015) simulations indicated that there was no substantial reduction in average seed cotton yield and soil water due to growing winter wheat as a cover crop.
... Hairy vetch (Vicia villosa) and rye grass (Lolium perenne) are annual cover crops utilized to improve nitrogen status in soil in no-till cropping systems (Hoffman et al., 1993). Previous studies of the influence of cover cropping, no-till, and reduced tillage practices on soil organic matter were conducted in temperate regions (Grandy and Robertson, 2007;Hermle et al., 2008), but recent findings suggest that combining cover crops with no-till practices and shifting tillage intensity may similarly enhance ephemeral and longer-term pools of soil organic matter in Mediterranean and semiarid annual agroecosystems (A´ lvaro-Fuentes et al., 2008;Veenstra et al., 2007). However, there are limited reports suggesting the effectiveness of cover crop species for protection of plants against plant pathogens. ...
... Non-CC areas remained undisturbed compared with areas prepared for CC seeding. Conventional tillage has been shown to disrupt wet and dry aggregates more than reduced tillage (Peixoto et al. 2006;Abdollahi et al. 2014;Veenstra et al. 2007), and rainfall has been shown to increase losses of soil organic carbon (SOC) through runoff, thereby reducing potential formation of aggregates (Jacinthe et al. 2004). This explains why wet aggregates were greater in non-CC areas compared with areas where CC were planted (Table 9). ...
White bean is a high value, important export field crop for farmers in Canada. Effective weed management in white bean is important as this crop is not competitive with weeds. Use of preplant incorporated, preemergence, and postemergence herbicides are effective means for weed control in white bean production in Canada. There are a range of herbicides registered for use on white bean in Canada, but in comparison to other high acreage field crops such as corn and soybean, the options are relatively limited. This can pose challenges for white bean producers trying to use multiple herbicide modes-of-action to reduce the evolution of herbicide resistant weeds, and limits management options for troublesome weeds. In particular, management of perennial weeds in white bean with currently registered herbicides is difficult. There is a continued need to evaluate and register additional herbicide options for weed management in white bean in Canada.
... However, other long-term studies have found that these systems result in improved soil quality (Karlen et al. 1994) and reduced erosion (Seta et al. 1993). In cropping systems similar to those in the Columbia Basin (irrigated vegetables), Veenstra et al. (2007) found that the combination of conservation tillage (e.g., high residue farming) and cover cropping resulted in increased soil organic matter levels, with most of the benefit coming from the cover cropping. ...
Farmers in the irrigated Columbia Basin of eastern Washington are using a variety of soil improvement practices: (1) organic amendments, (2) cover crops and green manures, and (3) high residue farming. To determine the effects of these practices, we compared the soils of fields managed under these practices to adjacent fields with no soil improvement practices. The soils were evaluated through an array of measurements in 2015. Results show that these practices can maintain or improve soils in this region, though each practice differs from the others in its specific effects. A parallel study estimated the economics of soil improvement and found that the improvement practices generated positive returns on investment.
... Although many economic and environmental impacts of wine production systems are actively being quantified, and while there is increasing scientific interest in the carbon footprint of vineyard management activities [e.g., 11], efforts to quantify C capture and storage in annual and perennial biomass remain less well-examined [12,13]. Studies from Mediterranean climates have focused mostly on C cycle processes in annual agroecosystems or natural systems [14,15]. Related studies have investigated sources of GHGs [16,17], on-site energy balance [18], water use [19] and potential impacts of climate change on productivity and the distribution of grape production [20]. ...
Background
Quantifying terrestrial carbon (C) stocks in vineyards represents an important opportunity for estimating C sequestration in perennial cropping systems. Considering 7.2 M ha are dedicated to winegrape production globally, the potential for annual C capture and storage in this crop is of interest to mitigate greenhouse gas emissions. In this study, we used destructive sampling to measure C stocks in the woody biomass of 15-year-old Cabernet Sauvignon vines from a vineyard in California’s northern San Joaquin Valley. We characterize C stocks in terms of allometric variation between biomass fractions of roots, aboveground wood, canes, leaves and fruits, and then test correlations between easy-to-measure variables such as trunk diameter, pruning weights and harvest weight to vine biomass fractions. Carbon stocks at the vineyard block scale were validated from biomass mounds generated during vineyard removal. ResultsTotal vine C was estimated at 12.3 Mg C ha−1, of which 8.9 Mg C ha−1 came from perennial vine biomass. Annual biomass was estimated at 1.7 Mg C ha−1 from leaves and canes and 1.7 Mg C ha−1 from fruit. Strong, positive correlations were found between the diameter of the trunk and overall woody C stocks (R2 = 0.85), pruning weights and leaf and fruit C stocks (R2 = 0.93), and between fruit weight and annual C stocks (R2 = 0.96). Conclusions
Vineyard C partitioning obtained in this study provides detailed C storage estimations in order to understand the spatial and temporal distribution of winegrape C. Allometric equations based on simple and practical biomass and biometric measurements could enable winegrape growers to more easily estimate existing and future C stocks by scaling up from berries and vines to vineyard blocks.
... sandy or highly fertilized soils). In terms of C sequestration, the use of CC has been proposed as a mean to enhance SOM and labile C pools by incorporating plant material into the soil (Veenstra et al., 2007). Average C sequestration potential of winter CCs (cultivated in the intercrop period of summer crops) has been reported at 0.32 AE 0.08 Mg C ha À 1 y À 1 at the global level (Poeplau and Don, 2015). ...
An integrated assessment of the potential of different management practices for mitigating specific components of the total GHG budget (N2O and CH4 emissions and C sequestration) of Mediterranean agrosystems was performed in this study. Their suitability regarding both yield and environmental (e.g. nitrate leaching and ammonia volatilization) sustainability, and regional barriers and opportunities for their implementation were also considered. Based on its results best strategies to abate GHG emissions in Mediterranean agro-systems were proposed. Adjusting N fertilization to crop needs in both irrigated and rain-fed systems could reduce N2O emissions up to 50% compared with a non-adjusted practice. Substitution of N synthetic fertilizers by solid manure can be also implemented in those systems, and may abate N2O emissions by about 20% under Mediterranean conditions, with additional indirect benefits associated to energy savings and positive effects in crop yields. The use of urease and nitrification inhibitors enhances N use efficiency of the cropping systems and may mitigate N2O emissions up to 80% and 50%, respectively. The type of irrigation may also have a great mitigation potential in the Mediterranean region. Drip-irrigated systems have on average 80% lower N2O emissions than sprinkler systems and drip-irrigation combined with optimized fertilization showed a reduction in direct N2O emissions up to 50%. Methane fluxes have a relatively small contribution to the total GHG budget of Mediterranean crops, which can mostly be controlled by careful management of the water table and organic inputs in paddies. Reduced soil tillage, improved management of crop residues and agro-industry by-products, and cover cropping in orchards, are the most suitable interventions to enhance organic C stocks in Mediterranean agricultural soils. The adoption of the proposed agricultural practices will require farmers training. The global analysis of life cycle emissions associated to irrigation type (drip, sprinkle and furrow) and N fertilization rate (100 and 300 kg N ha⁻¹ yr⁻¹) revealed that these factors may outweigh the reduction in GHG emissions beyond the plot scale. The analysis of the impact of some structural changes on top-down mitigation of GHG emissions revealed that 3–15% of N2O emissions could be suppressed by avoiding food waste at the end-consumer level. A 40% reduction in meat and dairy consumption could reduce GHG emissions by 20–30%. Reintroducing the Mediterranean diet (i.e. ∼35% intake of animal protein) would therefore result in a significant decrease of GHG emissions from agricultural production systems under Mediterranean conditions.
... In this sense, replacing winter intercrop fallow with cover crops (CCs) has been reported to decrease NO − 3 leaching via retention of post-harvest surplus inorganic nitrogen (N) (Wagner-Riddle and Thurtell, 1998), consequently improving N use efficiency of the cropping system (Gabriel and Quemada, 2011). Furthermore, the use of CCs as green manure for the subsequent cash crop may further increase soil fertility and N use efficiency (Tonitto et al., 2006;Veenstra et al., 2007) through slow release of N and other nutrients from the crop residues, leading to a saving in synthetic fertilizer. ...
Agronomical and environmental benefits are associated with replacing winter
fallow by cover crops (CCs). Yet, the effect of this practice on nitrous oxide
(N2O) emissions remains poorly understood. In this context, a field
experiment was carried out under Mediterranean conditions to evaluate the
effect of replacing the traditional winter fallow (F) by vetch (Vicia
sativa L.; V) or barley (Hordeum vulgare L.; B) on greenhouse gas
(GHG) emissions during the intercrop and the maize (Zea mays L.)
cropping period. The maize was fertilized following integrated soil fertility
management (ISFM) criteria. Maize nitrogen (N) uptake, soil mineral N
concentrations, soil temperature and moisture, dissolved organic carbon (DOC)
and GHG fluxes were measured during the experiment. Our management (adjusted
N synthetic rates due to ISFM) and pedo-climatic conditions resulted in low
cumulative N2O emissions (0.57 to
0.75 kg N2O-N ha−1 yr−1), yield-scaled N2O emissions
(3–6 g N2O-N kg aboveground N uptake−1) and N surplus (31 to
56 kg N ha−1) for all treatments. Although CCs increased N2O
emissions during the intercrop period compared to F (1.6 and 2.6 times in B
and V, respectively), the ISFM resulted in similar cumulative emissions for
the CCs and F at the end of the maize cropping period. The higher C : N
ratio of the B residue led to a greater proportion of N2O losses from
the synthetic fertilizer in these plots when compared to V. No significant
differences were observed in CH4 and CO2 fluxes at the end of the
experiment. This study shows that the use of both legume and nonlegume CCs
combined with ISFM could provide, in addition to the advantages reported in
previous studies, an opportunity to maximize agronomic efficiency (lowering
synthetic N requirements for the subsequent cash crop) without increasing
cumulative or yield-scaled N2O losses.
... Results from the project demonstrated that cover crop inputs and reduced tillage resulted in much lower soil disturbance and increases in SOM (Mitchell et al., , 2009; Veenstra et al., 2007). Various aspects and findings of the early stages of this longterm study including the ability of NT systems to increase soil C and N (Veenstra et al., 2006(Veenstra et al., , 2007Mitchell et al., 2009), reduce dust emissions (Baker et al., 2005) and production costs (Mitchell et al., 2009) and provide biomass to the soil via CC inputs (Mitchell et al., 2015) have been previously reported. Dust production was reduced by about 70% by the NT no cover crop (NO) treatment relative to the standard tillage (ST) NO system (Baker et al., 2005), soil C stocks increased with adoption of CC and NT (Mitchell et al., 2015), and computed values of the USDA Natural Resources Conservation Service (NRCS) soil conditioning index predicted SOM increases under NT and decreases under ST management (Mitchell et al., 2015). ...
The concept of soil health has attracted considerable attention during the past two decades, but few studies have focused on the effects on soil health of long-term soil management in arid irrigated environments. We investigated the effects of cover cropping and no-till management on soil physical and chemical properties during a 15-year experiment in California?s San Joaquin Valley (SJV) USA. Our objective was to determine if soil health could be improved by these practices in an annual crop rotation. The impact of long-term no-tillage (NT) and cover cropping (CC) practices, alone and in combination, was measured and compared with standard tillage (ST) with and without cover crops (NO) in irrigated row crops after 15 years of management. Soil aggregation, rates of water infiltration, content of carbon, nitrogen, water extractable organic carbon (WEOC) and organic nitrogen (WEON), residue cover, and biological activity were all increased by NT and CC practices relative to STNO. However, effects varied by depth with NT increasing soil bulk density by 12% in the 0?15 cm depth and 10% in the 15?30 cm depth. Higher levels of WEOC were found in the CC surface (0?5 cm) depth in both spring and fall samplings in 2014. Surface layer (0?15 cm) WEON was higher in the CC systems for both samplings. Tillage did not affect WEON in the spring, but WEON was increased in the NT surface soil layer in the fall. Sampling depth, CC, and tillage affected 1-day soil respiration and a soil health index assessment, however the effects were seasonal, with higher levels found in the fall sampling than in the spring. Both respiration and the soil health index were increased by CC with higher levels found in the 0?5 cm depth than in the 5?15 and 15?30 cm depths. Results indicated that adoption of NT and CC in arid, irrigated cropping systems could benefit soil health by improving chemical, physical, and biological indicators of soil functions while maintaining similar crop yields as the ST system.
... UC research on the effects of no-till agriculture in cotton and processing tomatoes has found that sustained management of no-till practices can achieve yields comparable to standard tillage (Mitchell, Klonsky et al. 2012;Mitchell et al. 2015) and can reduce seed banks of weeds (Shrestha et al. 2008). Benefits of this method include lower labor costs (Mitchell, Klonsky et al. 2012;Mitchell, Singh 2012), reduced particulate matter emissions (Baker et al. 2005) and less evaporative water loss (Mitchell, Singh et al. 2012), as well as increased soil carbon (Veenstra et al. 2007). While these results have served as a proof-of-concept, further studies on the commercial feasibility of this technique are needed to determine whether it can be widely adopted by California processing tomato growers. ...
A “healthy” soil can be thought of as one that functions well, both agronomically and ecologically, and one in which soil biodiversity and crop management work in synergy to suppress pests and diseases. UC researchers have pioneered many ways of managing soil biology for pest management, including strategies such as soil solarization, steam treatment and anaerobic soil disinfestation, as well as improvements on traditional methods, such as reducing tillage, amending soil with organic materials, and cover cropping. As managing for soil health becomes more of an explicit focus due to restrictions on the use of soil fumigants, integrated soil health tests will be needed that are validated for use in California. Other research needs include breeding crops for disease resistance and pest suppressive microbial communities as well as knowledge of how beneficial organisms influence plant health.
... In general, conservation tillage has not been practiced much in the arid, irrigated systems of California because of the diverse rotations and specialized field management practices needed for crop production in this region. Five years of winter cover crops (triticale, rye, and hairy vetch) and decreased tillage increased soil C in a cottontomato rotation in California (Veenstra, Horwath, and Mitchell 2007). Most of the SOC increase was found in the less stable light fraction form (particu-late organic matter) rather than in the more stable mineral-associated carbon form. ...
This publication is a timely update of the landmark 2004 CAST Task Force Report, Climate Change and Greenhouse Gas Mitigation: Challenges and Opportunities for Agriculture. Modern-day environmental issues include the need to decrease concentrations of carbon dioxide (CO2) and other greenhouse gases (GHGs) in Earth’s atmosphere. Agriculture is in the middle of this, and the challenges include adapting management and land use to cope with the changing climate and adopting mitigation strategies to decrease agriculture’s net contributions to GHG production. While agriculture deals with its key production roles, it also must consider conservation and the protection of natural resources. This report examines the current science to inform the public and policymakers about this crucial topic.
... Hairy vetch (Vicia villosa) and rye grass (Lolium perenne) are annual cover crops utilized to improve nitrogen status in soil in no-till cropping systems (Hoffman et al., 1993). Previous studies of the influence of cover cropping, no-till, and reduced tillage practices on soil organic matter were conducted in temperate regions (Grandy and Robertson, 2007;Hermle et al., 2008), but recent findings suggest that combining cover crops with no-till practices and shifting tillage intensity may similarly enhance ephemeral and longer-term pools of soil organic matter in Mediterranean and semiarid annual agroecosystems (A´ lvaro-Fuentes et al., 2008;Veenstra et al., 2007). However, there are limited reports suggesting the effectiveness of cover crop species for protection of plants against plant pathogens. ...
Water based crude extracts from hairy vetch (Vicia villosa) and ryegrass (Lolium perenne) were investigated for their antimicrobial activity against Rhizobium vitis, the causal agent of crown gall of grapevine (Vitis spp.), in a greenhouse. A total of 100 ml of each extract (125, 250 and 500 g·L-1) prepared from fresh and pounded shoots and roots was applied to grapevine cuttings once every 10 days. The shoot and root extracts displayed remarkable in vivo antibacterial effects, as indicated by reductions in gall formation by R. vitis of 24.97% to 75.02% in 'Kyoho' (susceptible to crown gall) and 100% in 'Campbell Early'(moderately resistant to crown gall) grapevines compared with the untreated control. The expression of several defense-related genes was investigated by quantitative real-time and semi-quantitative RT-PCR in two grapevine cultivars. Treatment with the extracts of hairy vetch and ryegrass led to differential induction of the accumulation of defense-related genes including β-1,3-glucanase (PR-2), phenylalanine ammonia-lyase (PAL), thaumatin-like protein (TLP), leucine reach-repeat (LRR), polygalacturonase inhibiting protein (PGIP), stilbene synthase (STS) and catalase (CAT). Expression analysis of defense related genes revealed noticeable differences between 'Kyoho' and 'Campbell Early' grapevines. Based on these results, extracts from tested cover crops can act as efficient biological inducers and therefore serve as an alternative strategy for grapevine crown gall protection.
... Cover crops are steadily gaining adoption by producers across the Great Plains as a cultural practice to improve soil health and crop yields (Dagel et al., 2014). Previous studies have shown that apart from providing N, winter legume cover crops can improve physical soil properties, reduce soil erosion, conserve soil water, recycle plant nutrients, and increase crop yield potential and soil productivity (Veenstra et al., 2007). The practical use of winter legume cover crops, however, is often limited by the asynchrony of cover crop planting windows and biomass accumulation with planting windows for summer cash crops (Janke et al., 2002). ...
Leguminous cover crops are considered part of sustainable agricultural systems. With the development of no‐till cropping systems, cover crops have been recognized for their ability to provide N for succeeding crops. The objectives of this study were: (i) to determine the N contribution of summer cover crops and double‐cropped grain crops following winter wheat (Triticum aestivum L.) and N rates to subsequent maize (Zea mays L.) crops’ physiological traits and yield, (ii) to calculate the fertilizer N replacement value, and (iii) to perform economic analyses of the cropping systems. Field experiments were conducted during the 2012–2013 and 2013–2014 growing seasons in Kansas. The grain yield of maize in all the cover crop systems and the double‐cropped soybean [Glycine max (L.) Merr.] system was similar to maize in the fallow system with 45 kg N ha⁻¹. The mean increase in grain yield as a result of including cowpea [Vigna unguiculata (L.) Walp.], pigeonpea [Cajanus cajan (L.) Millsp.], sunn hemp (Crotalaria juncea L.), double‐cropped soybean, and double‐cropped grain sorghum [Sorghum bicolor (L.) Moench] in the rotation over the fallow system with 0 kg N ha⁻¹ was 78, 91, 66, 72, and 12%, respectively. Fertilizer N replacement values for cowpea, pigeonpea, sunn hemp, double‐cropped soybean, and double‐cropped grain sorghum were 53, 64, 43, 47, and –5 kg N ha⁻¹, respectively. We conclude that the inclusion of summer leguminous cover crops in a cropping system has the potential to reduce or supplement N requirements and increase the grain yield of subsequent maize crops.
... Compared to the tilled vineyard at the top and middle depth, soil carbon was 27% higher in the no-till vineyard. Previous studies have also shown that soil carbon generally increases in the surface layer of soil under no-till practices (Paustian et al. 2000;Six et al. 2002), which decrease soil disturbance and therefore mineralization of carbon (Veenstra et al. 2007). However, soils appear to have a saturation point, at which their capacity to increase soil carbon reaches an equilibrium. ...
California growers could reap financial benefits from the low-carbon economy and cap-and-trade system envisioned by the state's AB 32 law, which seeks to lower greenhouse gas emissions statewide. Growers could gain carbon credits by reducing greenhouse gas emissions and sequestering carbon through reduced tillage and increased biomass residue incorporation. First, however, baseline stocks of soil carbon need to be assessed for various cropping systems and management practices. We designed and set up a pilot soil carbon and land-use monitoring network at several perennial cropping systems in Northern California. We compared soil carbon content in two vineyards and two orchards (walnut and almond), looking at conventional and conservation management practices, as well as in native grassland and oak woodland. We then calculated baseline estimates of the total carbon in almond, wine grape and walnut acreages statewide. The organic walnut orchard had the highest total soil carbon, and no-till vineyards had 27% more carbon in the surface soil than tilled vineyards. We estimated wine grape vineyards are storing significantly more soil carbon per acre than almond and walnut orchards. The data can be used to provide accurate information about soil carbon stocks in perennial cropping systems for a future carbon trading system.
... The OC in the oLF is protected by soil aggregates, consists mainly of cellular plant structures (Paul et al., 2008), and is related to the recalcitrance of litter (von Luetzow et al., 2006). In contrast, the OC of fLF did not increase in NatF, Alfa, F0C0, and F1C0 in our study, probably because this C pool turns over more quickly, most likely providing the substrate for the oLF fraction (Veenstra et al., 2007). The NatF and Alfa treatments could be expected to show increases in the SOC fraction (Nascente et al. 2013;Zagal et al. 2013); however, the low C content and insufficient C input limited C sequestration, probably because the small amount of labile C fraction was rapidly decomposed. ...
Soil organic carbon (SOC) is important to soil nutrient status in agroecosystems. Some of the soils of the Northeast of China, noted for their high SOC content, suffer from serious soil erosion to the point of having the parent material exposed or near the surface, which has raised concerns for food security. The Chinese Mollisols were derived from loamy Quaternary loess that developed from parent material. To effectively restore parent material to productive soils, information on the effects of land use/management practices on SOC concentration and C fractions in loess parent material of Chinese Mollisols is needed. The main objective of this study was to investigate the changes in C sequestration and C density fractions by physical and chemical fractionation (humic substances) occurring in the process of soil development from parent material under different management practices and land use. Six treatments were imposed in plots of loess parent material in a 5-year experiment: (1) natural fallow without weed control; (2) alfalfa; (3) soybean-maize rotation (S-M), straw of unfertilized maize removed; (4) S-M, straw of chemically fertilized maize removed; (5) S-M, straw of chemically fertilized maize and dried soybean powder incorporated; (6) S-M, biomass, including grain, of chemically fertilized maize incorporated. The SOC content increased by 15% to 77% depending on treatments. In the process of soil development, the C fractions of the parent material changed rapidly. The heavy fraction C pool accounted for a larger proportion of total SOC (78%–89%) than both the free light fraction (2.1%–10.2%) and the occluded light fraction (1.3%–12.9%) pools. The occluded light fraction was more sensitive than the free light fraction as indicator of soil C changes because of different land use and management practices. Humin accounted for a larger proportion (29.9%–54.7%) of SOC than fulvic acid (18.0%–34.4%), which was larger than the humic acid fraction (11.8%–14.8%). Our results indicate that SOC increase in loess parent material depends on types and amounts of organic matter inputs. The treatments, in which aboveground crop biomass and grain were incorporated, contributed more to C sequestration, distributions of density fraction, and humic substances than the treatments without organic matter. Management practices maximizing biomass inputs are recommended to restore SOC in degraded Chinese Mollisols in order to restore their fertility.
... balance cover cropping appears to be more important than tillage practices for retaining and increasing soil carbon, significantly increasing soil carbon content under all tillage scenarios (Veenstra et al., 2007, De Gryze et al., 2009). ...
Agriculture is under increasing pressure to produce more food with less environmental impacts and in the face of a changing climate. Management practices capable of sequestering soil carbon (C) and improving overall soil health hold promise for sustainable intensification, as well as climate change mitigation and adaptation. As market and policy-based incentives develop to support these practices, however, it is critical that adequate sampling protocols, minimum viable data sets, and thresholds of management responses to soil health indicators are identified across the diversity of cropping systems and edaphoclimatic conditions.
Much of the research into the impacts of agricultural management on soil C and soil health have been conducted in the Midwest, over the short-term, and to a shallow depth. Soil C dynamics and other soil health indicators are strongly influenced by climate and mineralogy, necessitating more research across a range of edaphoclimatic conditions. Further, detectable changes in soil C take decades to accrue, requiring long-term research. Proper accounting of changes in C stocks on a given acreage for climate mitigation strategies and economic incentive programs also necessitates sampling to a sufficient depth (minimum 1 meter or a root-limiting layer).
Using long-term, on-farm interventions, controlling for cropping system, climate and soil type, this work investigates the impact of soil health practices on soil C in surface and subsurface soils, as well as on a suite of physical, chemical, and biological soil properties commonly used to assess soil health. Deep soil cores at a long-term, industrial scale, agricultural research station in a Mediterranean-type climate indicated that 19 years of cover cropping with annual composted poultry manure applications (4t ha-1) increased soil C to a depth of 200 cm by +21.8 Mg ha-1 relative to a -4.8 Mg ha-1 loss under conventional management (Chapter 1). Trends also indicated potential losses of -13.4 Mg ha-1 under conventional management with cover cropping, despite increases of +1.4 Mg ha-1 in the surface 0-30 cm, stressing the importance of deep soil sampling for greenhouse gas accounting purposes.
Continuing the theme of deep soil C, a nearby regional survey of 10+ yr old hedgerows and adjacent cultivated fields across four soil types showed a strong impact of hedgerows on soil C to a depth of 100 cm, with an average difference of 3.85 kg C m-2 (0-100 cm) and few differences across the four soil types (Chapter 2). Most differences occurred in the surface 0-10 cm and the subsoil at 50-100 cm, indicating a dual role of surface management (litter accumulation, reduced disturbance) and deep, woody perennial roots. Soil type differences were only apparent in one of the four soil types, which differed substantially in parent material, mineralogy, and degree of weathering. Soil type did not influence the management effect and may indicate broad potential for hedgerows as a climate mitigation strategy. The magnitude of this strategy is limited, however, by the extent of hedgerows on a given farm/ranch.
Revegetation of field margins with hedgerows also had a positive impact on a broad suite of physical, chemical, and biological parameters (0-20 cm) commonly associated with soil health (Chapter 3). Hedgerow values were greater than cultivated fields for nearly every indicator in the surface 0-10 cm, commonly 2-3 times greater. Fewer, smaller differences were observed at 10-20 cm. Total soil C and N, available C, microbial biomass C, aggregate stability, and surface hardness were some of the most sensitive and least variable indicators of management type. Texture, pH, and bulk density were more indicative of soil type. A composite of variables was necessary to explain most of the variation in the data, indicating the complexity of soil health.
Among the crop production factors, preceding crop and tillage management affect the sustainable use of soil resources and ultimately crop growth and productivity. This study aimed at investigating the impact of preceding winter crops (grass or legume) and different tillage systems on forage yield, quality and nutritive values of three summer grass (Sudan grass, pearl millet and teosinte) and two legume forage crops (cowpea and guar) under arid conditions. The results exhibited that growing forage crops after legumes (as berseem clover) produced the highest fresh and dry forage yields and quality attributes compared with grasses (as wheat) with the exception of crude fiber content, which was decreased. Moreover, tillage practices showed positive impact on forage yields and quality attributes. The maximum forage yields and quality parameters were recorded under conventional tillage (CT) practice compared with reduced tillage (RT) and no-tillage (NT) systems. Among the evaluated crops, the highest yields of fresh forage, dry forage, crude fiber, crude protein and total digestible nutrient were exhibited by grass forage crops (Sudan grass, pearl millet and teosinte), whereas the highest crude protein content and the digestible energy values were produced by legume forage crops (cowpea and guar). The maximum fresh forage, dry forage, crude fiber, crude protein, total digestible nutrient and digestible crude protein yields were produced by pearl millet followed by Sudan grass under CT and RT after berseem clover. The highest net return was recorded by sowing pearl millet after berseem clover and applying CT followed by RT practices, which could be recommended for the commercial production. Moreover, it could be assumed that the combination of growing grass forage crops after legume crops under CT or RT systems could enhance forage crop yield and quality with an improvement in soil properties for sustainable agriculture with low cost and the highest net income.
Sequestering soil organic carbon (SOC) with cover crops (CCs) to mitigate climate change and enhance other soil ecosystem services is generating much enthusiasm. However, the potential of CCs to sequester large amounts of SOC appears to be debatable, which warrants further discussion on regional and national scales. This paper discusses both CC effects on SOC based on studies in the United States up to 30 May 2021 and practices that could enhance CC ability to sequester SOC. Cover crops accumulated SOC only in 22 (29%) of 77 comparison (CC vs. no CC) counts. Cover crops accumulated 0.2–0.92 Mg C ha⁻¹ yr⁻¹ (0.41 Mg C ha⁻¹ yr⁻¹ average) across the 22 comparisons where CCs increased SOC and 0–0.92 Mg C ha⁻¹ yr⁻¹ (0.12 Mg C ha⁻¹ yr⁻¹ average) across the 77 comparisons in the upper 30‐cm soil depth. Cover crops increased SOC most in low‐C soils (<1% C) and after 5 yr but not when CCs produced <2 Mg biomass ha⁻¹. Because SOC accumulation was primarily correlated (r = .38; p = .006) with CC biomass and years under CCs (r = .37; p = .009), current CC management practices need modification to enhance SOC accumulation. Planting after crop harvest in summer and terminating late to increase CC biomass production along with long‐term (>5 yr) use can be potential strategies. Overall, CCs can accumulate SOC only in one‐third of cases based on U.S. studies, which urges the modification of current CC management practices to boost SOC sequestration.
Tillage disturbs the soil and causes soil erosion. Various conservation tillage mechanisms are undertaken to reduce erosion, and one such is no-till. No-till (NT) is the method by which crops are raised every year without disturbing the soil. The advent of machinery that helps drilling in either through crop residues or cover crop mulch has helped reduce soil erosion and increased the spread of NT farming. The impact of NT on increasing crop yields has been researched upon with varying results. The adoption incentive is always increased yield for the producer, and cover cropping is one major recommendation for yield improvements through NT. Cover crops can be grown as sole crop or a mixture to enable exploiting different layers of the soil, help fixing atmospheric nitrogen, improve soil nutrient status, improve soil porosity, and, above all, produce maximum biomass to help build the soil and prevent erosion. Cover crops as a feature in organic or conventional rotations must be thought as to why and where they fit into the rotation. Planting and termination dates have to be coordinated between the cover crop and chosen cash crop so that they do no overlap but have a wide enough growth window. It is important for the cover crop to produce maximum biomass, but the cash crop must also be planted at the right time for the critical yield to be maintained or improved. Research that is innovative and balances conservation of soil with increased crop yields should be the best serving option that needs to be developed, and it is fairly obvious to turn to cover cropping.
Various responses of plant growth attributes to the combined application of biochar and mineral fertilizers were reported according to trial conditions. Thus we studied the effects of biochar combined with nitrogen and phosphorous fertilizers on crop growth and yield and NUE of maize crop under alkali clay soil. Field trial during two successive seasons (2018 and 2019) was conducted to investigate the possibility of biochar addition (0, 6 and 12 Mg ha⁻¹), as well as, P (0 and 37 kg P2O5 ha⁻¹) and N (95, 190 and 285 kg N ha⁻¹) fertilizations on maize and some nitrogen use efficiencies attributes. The results revealed that, biochar addition at 6 or 12 Mg ha⁻¹ resulted in a significant reduction in plant height, stem diameter and ear length compared with the control treatment. In contrast, biochar applied recorded significant increase in both leaves area per plant, grain yield and yield attributes, as well as, grain protein content, NUE, grain-NUtE, as well as, total-NUpE compared by control treatment. Applying 190 kg N ha⁻¹ caused significant increase in each of growth and grain yield attributes, as well as, grain-NUtE. Biochar addition by 6 or 12 Mg ha⁻¹ combined with P (37 kg P2O5 ha⁻¹) and N (190 or 285 kg N ha⁻¹) application had the greater effect on increasing stem diameter, ear length, almost yield attributes, NUE, as well as, grain-NUtE. However, NUE and total-NUpE showed negative response to biochar added with N fertilizer.
This paper examines opportunities for the United Nations Framework Convention on Climate Change (UNFCCC) to consider financial mechanisms for the uptake of conservation agriculture (CA) practices in developing countries to reverse the loss of soil organic carbon. Conservation agriculture, commonly described as the reduction of tillage, maintaining soil cover and introducing crop rotations, is currently being promoted by the United Nations Food and Agriculture Organisation as the most sustainable form of farming into the future. It was found that the increasing uptake of CA practices by developed countries improved soil organic carbon benefit and reduced energy inputs. Furthermore industrial agriculture has evolved a range of new technologies that can be adapted in developing countries to improve food security, increase environmental benefits and provide carbon offsets. This is in line with the climate change mitigation strategy of putting atmospheric carbon back in the soil to increase soil organic carbon. It is also noted that recognising conservation agriculture methodologies in carbon offset schemes would require the development of alternative economic instruments specifically to support small landholder changes in farming practices such as exist for hydrological and biodiversity ecosystem services schemes. Some of the constraints for small landowners providing agricultural carbon offsets are investment capital and an established trading mechanism that recognises the inherent issues of agriculture. Adaptation of conservation agricultural practices from industrialised agriculture to developing countries is examined along with current offset schemes being proposed in developed countries. A review of the literature examines Payment for Ecosystem Services (PES) and suggests a number of methodologies for consideration as part of an offset market. It was found that the two main obstacles in market terms are the acceptance of a level of soil carbon sequestration that can be easily calculated and the degree of attached liability for farmers in selling the equivalent of a Certified Emission Reduction unit from a highly volatile system.
Agronomical and environmental benefits are associated with replacing winter fallow by cover crops (CC). Yet, the effect of this practice on nitrous oxide (N2O) emissions remains poorly understood. In this context, a field experiment was carried out under Mediterranean conditions to evaluate the effect of replacing the traditional winter fallow (F) by vetch (Vicia sativa L.; V) or barley (Hordeum vulgare L.; B) on greenhouse gas (GHG) emissions during the intercrop and the maize (Zea mays L.) cropping period. The maize was fertilized following Integrated Soil Fertility management (ISFM) criteria. Maize nitrogen (N) uptake, soil mineral N concentrations, soil temperature and moisture, dissolved organic carbon (DOC) and GHG fluxes were measured during the experiment. The ISFM resulted in low cumulative N2O emissions (0.57 to 0.75 kg N2O-N ha−1), yield-scaled N2O emissions (3–6 g N2O-N kg aboveground N uptake−1) and N surplus (31 to 56 kg N ha−1) for all treatments. Although CCs increased N2O emissions during the intercrop period compared to F (1.6 and 2.6 times in B and V, respectively), the ISFM resulted in similar cumulative emissions for the CCs and F at the end of the maize cropping period. The higher C:N ratio of the B residue led to a greater proportion of N2O losses from the synthetic fertilizer in these plots, when compared to V. No significant differences were observed in CH4 and CO2 fluxes at the end of the experiment. This study shows that the use of both legume and non-legume CCs combined with ISFM could provide, in addition to the advantages reported in previous studies, an opportunity to maximize agronomic efficiency (lowering synthetic N requirements for the subsequent cash crop) without increasing cumulative or yield-scaled N2O losses.
The effect of tillage systems were evaluated on different pools of C and N in soil and their distribution and turnover time in soil size fractions of a maize cropped field. Soil samples were incubated to determine mineralizable C and N. Previously, C and N microbial biomass, and total C and N were determined. Samples were also separated into different aggregate sizes by wet sieving, and δ13C analyzed. In general, cropping corn with conventional tillage (LC) and minimum tillage (ML) increased recalcitrant C and N of the soil, but decreased the labile fraction of C as microbial and nonmicrobial biomass, as compared with the no-tillage system (SD). After 8 years, the largest aggregate sizes (>250 μm) increased by 8% under SD, decreased by 10% under LC, and showed no changes under ML. The smallest amount of sequestered C was observed in the microaggregates (means of 2.94 kg·m-2) compared to macroaggregates (4.2 kg·m-2). The organic matter turnover time was higher for ML and LC as compared to SD. Under the conditions of this study, it was found that storage of C in tropical soils can be possible by the adoption of proper management techniques, such as a no-tillage system.
We evaluated the mode of decomposition in relation to biochemical quality of plant residues and land use. Alfisols under different uses (woodland, grassland and cultivated soils) mixed with alfalfa (Medicago sativa L.) and wheat straw (Triticum aestivum L.) in doses of 10 t ha -1 (dry weight) were incubated in laboratory, in triplicate. CO 2 emitted from soil was measured after 20, 40, 60, and 80 h of incubation, and the amount of released C was calculated (mg C g -1 soil). The difference between the amount of C added by the plant residue and C liberated as CO 2, was named residual C. The C loss was greater and residual C retained was lower (p<0.05) for Alfisols where alfalfa was applied than for those were wheat straw was added, which was a function of the biochemical composition differences between the alfalfa and wheat straw residues. Regarding the land use, residue C loss was lower (p<0.05) in woodland (Haematoxylon campechianum and Bucida buceras) soils (rates from-0.12 to-1.02 μg g -1 /day), and greater in grassland (Gramineae) and cultivated soils (Sorghum vulgare and Yucca sp.) (rates from-0.28 to-1.37 μg g -1 /day). We conclude that the C loss, by decomposition, increases in order of woodland > grassland > cultivated soils, and less residual C is retained.
Increasing costs, changing markets and, off-site environmental concerns have
generated interest in the use of innovative tillage systems and crop rotations that improve
soil quality and long term sustainability of local production systems. The Objectives of this
study were to determine how alternative dryland winter wheat and irrigated sugar beet
cropping systems impact (i) soil organic matter processes (ii) microbial populations and
diversity, and (ii) profitability.
On-farm field studies were conducted from 2007-2009 in Wyoming’s
southeastern wheat-producing region and in the Big Horn Basin. Soil, crop, and economic
data were collected from non-irrigated fields under conventional wheat-fallow, organic,
no-till, minimum till, and long-term grass in southeastern Wyoming. In the Big Horn Basin
samples were collected from irrigated fields under five different crop rotations: sugar beetbarley,
sugar beet-barley-bean, red clover-red clover-bean-bean, sugar beet-bean, and
sugar beet-sugar beet-alfalfa-alfalfa.
In the wheat study, our results show that conservation tillage allows increased
cropping intensity; reduced fallow periods while simultaneously increasing wheat grain
and residue yield, and improving soil quality. Conservation tillage also increased both the
cost of production and the profitability of dryland production systems, especially when
coupled with higher precipitation. Data suggests that low adoption of conservation
2
cropping systems in Southeastern Wyoming compared to surrounding states may be an
extension issue, coupled with high conversion costs.
Results of the sugar beet study show that longer crop rotations that include
legumes improved sugar beet root and top dry matter yield and soil quality, but not
economic benefits. In this production system innovative crop rotations offered
environmental benefits that extended beyond the farm gate, suggesting that there may be a
rationale for public subsidies to support continued provision of these socially beneficial
externalities.
Rising costs and air quality regulations have created interest in California’s San Joaquin Valley (SJV) in production systems that reduce tillage operations and soil disturbance. From 1999 to 2009, we evaluated conventional (CT) and reduced tillage (RT) systems for a cotton (Gossypium hirsutum L.)/tomato (Solanum lycopersicon Mill.) rotation with (CC) and without (NO) cover crops in a Panoche clay loam soil (fine-loamy, mixed, superactive, thermic Typic Haplocambid) in Five Points, CA, in terms of yield, soil C, and the NRCS soil conditioning index (SCI). The RT reduced tractor operations by 50% for tomato and 40% for cotton. Cover cropping produced 38.7 t ha-1 of biomass. Tomato yields were 9.5% higher in RT vs. CT systems and 5.7% higher in NO vs. CC systems. The CT cotton yields were 10.0% higher than RT yields and 4.8% higher in NO systems, but yield patterns were not consistent from 2005 to 2009. Soil C content was uniform (0-30-cm depth) in 1999 (19.72 t ha-1) and increased in all systems in 2007 (t ha-1): RTCC 29.11, CTCC 26.36, RTNO, 24.09, and CTNO 22.65. Soil C content ofRT and CT systems did not differ, but was greater in CC than in NO systems. In the 0- to 15-cm depth, RT increased soil C, indicating stratification, and also increased C in the occluded light and mineral fractions. The SCI was positive for RT treatments, predicting a soil C increase, and negative for CT systems, predicting a soil C decline, but measured soil C content increased in all systems. Results show that RT maintains or increases yields relative to CT, and CC stores more soil C than NO. © 2015 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved.
The use of no-tillage has notably increased in the Pampas region of Argentina during the last 10 yr. Two tillage experiments with contrasting previous agricultural use, degraded and non-degraded soils, were evaluated in the southeast of Buenos Aires province, Argentina. The objectives were to: (i) quantify the effects of tillage and N fertilization on quantity and vertical distribution of C and N in the soil organic matter (SOM) and particulate organic matter (POM) fractions as well as potentially mineralizable N (PMN), and (ii) evaluate these fractions as indicators of soil quality. Tillage systems were conventional tillage (CT), minimum tillage (MT), and no-tillage (NT) (main plots), and N fertilization rates were 0, 120, and 150 kg ha -1 (subplots). Total organic C (TOC), total N (TN), POM-C, POM-N, and PMN were measured at 0- to 7.5- and 7.5- to 15-cm soil depth. In Exp. I (degraded soil) TOC was greater under NT (27 g kg-1) than under CT (24 g kg-1) in the 0-N treatments. No differences in TOC and TN were found in Exp. II at 0 to 7.5 cm (non-degraded soil). Carbon in POM and POM-N were greater under NT in the fractions of 212 to 2000 and 53 to 212 μm at 0 to 7.5 cm, but they were similar or greater under CT at 7.5- to 15-cm depth in Exp. I. Stratification of TOC, TN, and POM were observed under NT in Exp. I. Potentially mineralizable N was greater under NT (62 mg kg-1) hi Exp. I, however, no differences hi PMN were observed hi Exp. II. Carbon in POM 212 to 2000 μm and PMN were the more sensitive indicators of tillage effects, mainly in Exp. I.
A simple densimetric method for the separation of free and occluded particulate organic materials was developed and applied to five virgin soils. The free organic matter was isolated by suspending the soil in sodium polytungstate solution (d = 1.6 Mg m-3) and decanting the light material. The remaining soil was disaggregated by sonification for liberation of occluded organic materials. The free light fraction consisted of large, undecomposed or partly decomposed root and plant fragments. This fraction comprised 0.59-4.34% of soil dry weight and accounted for 6.9-31.3% and 5.9-22.1% of total soil carbon and nitrogen respectively. Identifiable components of the occluded fraction were small particles of incompletely decomposed organic residues, pollen grains, particles of plant tissue such as lignin coils and phytoliths. This fraction comprised 0.69-1.81% of soil dry weight and represented 9.2-17.5% and 6.2-14.1% of the total soil carbon and nitrogen. The proportion of soil organic carbon recovered as the occluded fraction was high in soils with high clay contents. The chemical composition of occluded and free organic materials was investigated by solid-state 13C CP/MAS NMR spectroscopy. Despite the differences in soils, environmental conditions and vegetation, the organic structure of the free light fraction was similar in four of the five soils. This fraction consisted of 55-63% O-alkyl C, 18-25% alkyl C, 14-18% aromatic C, and 5-7% carbonyl C. In the other soil, this fraction showed a higher proportion of alkyl C (31%) and lower O-alkyl C (46%). Most of the differences between soils were associated with organic materials contained in the occluded light fraction. The differences in chemical structure between the occluded light fraction and free light fractions were similar in all examined soils. The NMR data showed that the proportion of O-alkyl C was lower and alkyl C higher in the occluded light fractions than in the free light fractions. The proportion of aromatic and carbonyl carbon was higher in the occluded fractions of three soils while the percentage of these two types of carbon remained unchanged in the two other soils. It is considered that the occluded organic matter is an old pool of carbon that has been accreted within aggregates during decades of root growth and it is that pool which is lost due to cultivation.
Soil quality is a composite measure of both a soil’s ability to function and how well it functions, relative to a specific use. Soil quality can be assessed using a minimum data set comprising soil attributes such as texture, organic matter, pH, bulk density, and rooting depth. Soil organic matter has particular significance for soil quality as it can influence many different soil properties including other attributes of the minimum data set. Assessment of soil organic matter is a valuable step towards identifying the overall quality of a soil and may be so informative as to be included in minimum data sets used to evaluate the world’s soils.In this review, soil organic matter is considered to encompass a set of attributes rather than being a single entity. Included among the attributes and discussed here are total soil organic carbon and nitrogen, light fraction and macroorganic (particulate) matter, mineralizable carbon and nitrogen, microbial biomass, soil carbohydrates and enzymes. These attributes are involved in various soil processes, such as those related to nutrient storage, biological activity, and soil structure, and can be used to establish different minimum data sets for the evaluation of soil organic matter quality. Key words: Biological activity, minimum data set, nutrient storage, soil organic matter, soil quality, soil structure
13 CO2 and followed both tally distinct in terms of interactions with soil microbial root- and shoot-derived C in total soil organic C (SOC) and labile C systems because C inputs from roots include root pro- pools for the first growing season following hairy vetch incorporation. duction, turnover, and exudation. The influence of roots At the end of the growing season, nearly one-half of the root-derived on SOC pools could be relatively greater than the influ- C was still present in the soil, whereas only 13% of shoot-derived C ence of aboveground C inputs because of the continuous remained. A greater proportion of root-derived C was found as oc- release of C from roots and the complex nature of the cluded POM and associated with the clay and silt fraction. Greater associated with the use of green manures. Furthermore, on the basis In SOM dynamics studies, particular attention is given of these findings, we hypothesize that the greater retention of root- to the POM fraction. This fraction, composed mainly derived C in the first 6 mo of decomposition will increase the persis- tence of this C in SOM in the long term. of plant residues in different stages of decomposition, is regarded as a labile pool of SOM and is very sensitive to changes in C input and loss with time (Christensen,
Fractions of soil organic matter (SOM) were obtained from three soils using alternative physical fractionation procedures, and evaluated against the requirements of model pools. We compared two-stage density fractionation (isolating free and intra-aggregate fractions, before and after dispersion, respectively) with particle-size separation of dispersed soil. For full comparison, the organomineral fraction residual from density fractionation was also size separated. In standardizing the density-based method, we found recovery of intra-aggregate organic matter highly sensitive to separation density as compared with the free. Recovery of the intra-aggregate was also influenced by dispersion energy. The greatest amount was obtained using a combination of the highest density (1.80 g cm-3) and dispersion energy (1500 J g-1). Analysis by 13C nuclear magnetic resonance (NMR) showed O-alkyl/alkyl-C ratios 1.38 to 2.30 times greater in intra-aggregate organic matter than in the free. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) also indicated a greater proportion of aliphatic hydrocarbon, carboxylic anions, and aromatic C in intra-aggregate organic matter. The findings suggest this fraction comprises more decomposed and transformed organic matter relative to the free. Higher signal/noise ratios in NMR spectra of particle-size fractions (compared with their organomineral equivalents) were attributed to C in particulate SOM, not removed by prior density separation. Whilst particle-size fractions confuse particulate SOM with that attached to mineral surfaces, fractions isolated by two-stage density separation are small in number and display distinct chemical properties. We suggest they provide a sound basis for a model of SOM turnover based on measurable pools.
Soil degradation due to tillage has been reported Africa-wide. Other main causes of soil degradation are overgrazing, extensive cultivation of marginal lands, widespread clearing of vegetation for agriculture, deforestation, exploitation of unsuitable agricultural technologies, mis-management of arable lands, and frequent drought. Hence, declining soil fertility and increasing population pressure on lands are fragile bases on which to build expectations for improved crop production. This paper recognizes conservation tillage systems as one means for preventing food shortages and natural resources degradation throughout the continent. Conservation tillage has the potential for increasing soil organic matter content and enhancing soil aggregation. Conservation tillage systems can create an aggregated, fertile surface layer that is important from a soil erosion reduction perspective and thus for a sustainable agriculture in Africa. Some indigenous tillage systems in Africa can be adapted to meet objectives of conservation tillage systems. Further, recent technological developments in tillage and seeding machinery will certainly enhance the rate of farmer’s acceptance and adoption of conservation tillage.
To take advantage of conservation tillage systems (including direct drilling and non-inversion) in central Iran, it is important to study the effects of different cultivation practices on soil structural stability as a physical indicator. A four-year study was conducted to investigate the effects of seven tillage systems on aggregate properties of a clay-loam soil (Calcic Cambisol) with continuous wheat (Triticum aestivum L.) production. Crop productivity was also evaluated. Tillage treatments were moldboard plowing+disking (MD) as conventional tillage; chisel plowing +disking (CD); chisel plowing+rotary tilling (CR); chisel plowing (twice)+disking (2CD); plowing with Khishchi (a regional rigid cultivator)+disking (KD) as non-inversion methods; and till-planting with cultivator combined drill (TP); and no-till (NT) as direct drilling methods. A randomized complete block design consisting of four replications was used. Samples were taken from three different soil depths. A wet sieving method was used to determine aggregate size distribution (ASD), and mean weight diameter (MWD) as indices of soil aggregate stability. Soil organic carbon was also determined. For the first three years of the experiment, ASD and MWD at 0–15 cm were similar in different tillage treatments, except for direct drilling which had a significantly higher amount of aggregate greater than 2 mm and 2–1 mm diameter compared to the conventional method. At the second and third sampling depths all treatments had similar influence on ASD and MWD. Tillage treatments showed a significant effect on ASD and MWD in the fourth year of the experiment in all three depths. Almost 70% of the aggregates in the MD system were less than 0.25 mm, while only 55% of the aggregates in the direct drilling methods were less than 0.25 mm diameter. The four-year yield average for conventional and non-inversion tillage systems was 7264 and 6815 kg ha−1, respectively. Although, direct drilling improved soil structural stability, its lower yield (5608 and 4731 kg ha−1 for TP and NT, respectively) potential would indicate that reduced tillage systems (i.e. CD) appear to be the accepted alternative management compared to conventional practice (MD).
Organic C and natural 13C abundance were measured in a forest soil and a soil under corn (Zea mays L.) to assess management-induced changes in the quantity and initial source of organic matter. The total mass of organic C in the cultivated soil was 19% lower than in the forest soil. It was estimated that after 25 yr of continuous corn, 100 Mg C ha-1 was returned to the soil as residues, of which only 23 Mg ha-1 remained in the soil; 88% of the remaining corn-derived C (C4-derived C) was in the plow layer. About 30% of the soil organic C in the plow layer (0-27 cm) was derived from corn. The mineralization of C from native organic matter associated with the coarse silt fraction was the slowest of all particle-size fractions. -from Authors
The effects of no-tillage (NT) and moldboard plowing (MP) on the distribution and storage of soil organic carbon (SOC) and different C fractions were determined along a transect on a private farm in southern Ontario, Canada, where a paired NT and MP strip traversing three soil series had been in existence for 19 yr. Soil samples were collected to a depth of 60 cm in seven increments. SOC was determined in each sample and for the top 30 cm, the organic carbon was fractionated into loose-, occluded-particulate organic matter (loose-POM and occluded-POM) and humified fraction (HF). After 19 yr, soils under NT contained significantly (P < 0.05) more SOC than soils under MP on both an equivalent depth basis and an equivalent mass basis. Greater concentrations of loose- and occluded-POM were found in NT than MP surface soils (0-10 cm). MP favored higher loose-POM contents than NT practices at a depth of 10-20 cm. The HF fraction accounted for most of the increase in SOC in the Huron and Brady soils, whereas the occluded POM accounted for more of the increase in the Fox soil. Our results indicate that the extent of SOC sequestration under NT is strongly dependent on soil type and cropping history.
No-till practices have the potential to increase soil organic C, but little is known about the relative contribution of surface residue and roots to soil organic C accumulation. In a simulated no-till experiment, we studied the fate of 14C-labeled surface residue and in situ roots during a 1-yr incubation. Soil samples collected during the incubation were chemically dispersed and separated into five particle size and density fractions. The organic C, 14C, and total N content of each fraction was determined. Alkali traps were used to measure 14C losses due to respiration. After 360 d, 66% of the 14C contained in the surface residue on Day 0 had been respired as 14CO2, 11% remained in residue on the soil surface, and 16% was in the soil. In comparison, 56% of the root-derived 14C in the soil was evolved as 14CO2 and 42% remained in the soil. The large (500-2000 μm) and small (53-500 μm) particulate organic matter (POM) fractions together contained 11 to 16% of the initial root-derived 14C in the soil. In contrast, POM contained only 1 to 3% of the initial surface residue-derived 14C. These data show clear differences in the partitioning of surface residue- and root-derived C during decomposition and imply that the beneficial effects of no-till on soil organic C accrual are primarily due to the increased retention of root-derived C in the soil.
In long-term experiments on soils ranging from sand to peat, which had been ploughed or naturally compacted following the use of herbicides, crop yields and the variation with depth of OM, plant nutrients and roots were compared. It was concluded that temperate cereals, maize and many cover crops might be successfully grown on compacted soils, but the growing of sugar beet and potatoes, and to a lesser extent of peas and beans, was hazardous, though in many cases yields were not depressed. CCT. (Abstract retrieved from CAB Abstracts by CABI’s permission)
The use of 13C natural abundance (δ13C) to follow C input to soil has gained widespread acceptance. However, inorganic C present in the soil as carbonates will interfere with the measurement of soil organic 13C unless removed or excluded from measurement. We report a simple and convenient HCl-fumigation method to remove inorganic C from soil. Soil samples are weighed in Ag-foil capsules, arranged on a microtiter plate, wetted with water to approximately field capacity, and placed in a desiccator containing a beaker with concentrated (12 M) HCl. The carbonates are released as CO2 by the acid treatment in 6 to 8 h. The soil samples are then dried at 60°C prior to isotope determination. The advantages of the HCl-fumigation method to remove inorganic C from the soil are that: (i) no water soluble C will be lost from the soil; (ii) a large number of samples can be processed simultaneously; (iii) the removal of inorganic C is rapid and complete; and (iv) the method could also be used to determine both organic and inorganic C content in the soil. A potential disadvantage, however, is that the HCl fumigation changed the 15N natural abundance of soil N.
Several long-term studies suggest that no-till (NT) practices do not increase soil organic matter (SOM) sequestration in all situations. We evaluated the interaction of tillage and soil texture effects on SOM in Illinois Mollisols and Alfisols by characterizing particulate organic matter (POM), potentially mineralizable N (PMN), and soil microbial biomass (SMB). Thirty-six fields were sampled during spring and summer of 1995 and 1996. Each field had been under either conventional tillage (CT) (disc, moldboard plow, and/or chisel plow) or NT management for at least 5 yr. No-till fields contained 15% (3.0 g C kg -1 soil) more soil organic C (SOC) than CT fields in the 0- to 5-cm depth; however, tillage did not affect SOC contents in the 5- to t5- or 15- to 30-cm depths, or in the overall sampling depth (0-30 cm). Fields under NT contained 33% more POM (1.4 g C kg -1 soil) and 54% more PMN in the 0- to 5-cm depth, but there was no tillage effect on POM (0-15 cm) or PMN (0-30 cm) contents overall. Average POM contents were 29% lower (0.73 g C kg -1 soil) in the 5- to 15-cm depth of the NT than of the CT soils. At sand contents below 50 g kg -1 soil, NT fields contained greater SOC, total N, and POM contents in the 0- to 5-cm depth and lower POM contents in the 5- to 15-cm depth than CT fields. In soils with sand contents higher than 50 g kg -1 soil, tillage practices did not affect the vertical distribution of SOC, total N, or POM.
This study examined the effects of bare fallow, stubble mulch fallow, and no-till fallow management on aggregate size distribution and organic C and N contents. Mineral-associated organic matter was isolated by dispersing in sodium hexametaphosphate and removing the sand and particulate organic matter (POM) by passing through a 53-μm sieve. A large proportion of the total soil dry weight (50-60%) was isolated in the 250-2000 μm aggregate size class. The native grassland soil was more stable than the cultivated soils when slaked, and the no-till was more stable than the stubble mulch and bare fallow soil when slaked. The data reported relates the loss of structural stability from cultivation to losses of organic C and N from the POM fraction. -from Authors
The straw and stubble of spring barley (Hordeum vulgare; 5t dry matter ha−1) were either burned or incorporated into soil annually for 18 yr in two field experiments in Denmark. Both experiments were on light soils situated at Studsgaard (loamy sand) and Rønhave (sandy loam).At both sites 18 yr of annual straw incorporation increased total soil organic C by only 5% and total N by about 10% but produced large increases in microbial biomass measured by the CHCl3-fumigation method. The increases in biomass C were 45 and 37% at Studsgaard and Rønhave, respectively: the corresponding increases in biomass N were 50 and 46%. Biomass measurements thus gave an early indication of slow changes in organic matter content long before these could be measured accurately against the background of organic matter already present in the soils. Increases in biomass P due to straw incorporation appeared to be even greater. However, the amounts of P released by CHC13 were small so the measurements of biomass P were less accurate than those of biomass C or N.During a 60-day laboratory incubation at 25°C, evolution of CO2-C was 55–79% greater in soil from straw incorporated plots than in soil from burned plots. Mineralization of N was 40–50% greater where straw had been incorporated, indicating thaf the long-term incorporation of straw had increased the quantity of mineralizable N in soil.
This work corroborates the hierarchical conceptual model for soil aggregate structure presented by Tisdall and Oades (1982), extends it to North American grassland soils, and elaborates on the aspects relating to the influence of cultivation upon losses of soil organic matter. Aggregate size distributions observed for our soils are very similar to those of Australian soils, indicating that the microaggregate‐macroaggregate model may hold for a wide array of grassland soils from around the world. The use of two wetting treatments prior to sieving demonstrated that the native sod soil had the same general structural characteristics as cultivated soil but the macroaggregates were more stable. When slaked, native and cultivated soil present in the microaggregate size classes had less organic C, N, and P than the soil remaining as macroaggregates, even when expressed on a sand‐free basis. Moreover, the C/N, C/P, and N/P ratios of microaggregates were narrower than those of macroaggregate size classes. Much more C and N was lost than P under the conditions of this study. Element‐specific differences in microbial catabolic processes vs. extracellular enzyme activity and its attendant feedback controls are postulated to account for this difference. When the macroaggregates were crushed to the size of microaggregates, mineralizable C as a percent of the total organic C was generally greater for macro‐ than microaggregates early in the incubation for the cultivated soil and throughout most of the incubation for the native sod soil. Mineralizable N as a percent of the total organic N was greatest in macroaggregates even when the macroaggregates were not crushed. The macroaggregate‐micraggregate conceptual model is applied to help explain accumulation of soil organic matter under native conditions and its loss upon cultivation.
Adoption of conservation tillage practices has been much slower on irrigated land than on dryland in southern Alberta. This study investigates the effect of conventional tillage (CT) and minimum tillage (MT) on soil physical properties for two crop sequences on an irrigated Dark Brown Chernozemic clay loam from 1994 to 1998. For soft wheat and annual legumes, CT consisted of chisel plowing and double discing in the fall and light duty cultivation and harrow packing in spring. The MT treatment consisted of only light cultivation and harrow packing in spring. For sugar beets, CT consisted of moldboard plowing, double discing, light cultivation, harrow packing and ridging in fall and de-ridging in spring, while MT consisted of chisel plowing, harrow packing and ridging in the fall and de-ridging in the spring. Crop sequence 1 was spring wheat (Triticum aestivum L.)–sugar beet (Beta vulgaris L.)–spring wheat–annual legume, while sequence 2 was spring wheat–spring wheat–annual legume–sugar beet. Soil physical properties measured included bulk density (BD) and cone index (CI) after 1 and 5 years of treatment and soil aggregation and residue cover after 4 years of treatment. There were no significant differences between MT and CT for BD and CI. Use of MT resulted in a larger geometric mean diameter (GMD) of aggregates (6.52mm) and a lower erodible fraction (EF) of 23.4% compared to a GMD of 3.81mm and an EF of 31.5% (EF) for CT. Use of MT also resulted in better residue cover than CT, reducing susceptibility to wind erosion. Crop sequence is crucial to the successful implementation of MT systems. Since the two crop sequences tested resulted in similar soil physical conditions after 5 years, each could be successfully used with MT for irrigated cropping in southern Alberta.
Crops have been grown in the subhumid and semiarid Argentinean Pampas for over 50 years using tillage methods (intensive plowing) introduced from more humid regions. As a result, soil degradation due to erosion by wind and water has been moderate to severe. Experiments to control erosion through use of conservation systems were initiated at six semiarid and subhumid sites in the Argentinean Pampas between 1976 and 1990 and conducted for 5 to 11 years. In this paper, we summarize the effect of conventional and conservation tillage treatments on some soil properties and crop yields. Most soil physical, chemical, and biological properties were improved by conservation systems, but the rate of change differed due to climatic and soil differences among sites, with the difference due to tillage generally being greater at the more humid sites with loamy soils than at the drier sites with sandier soils. Crops with a large N requirement yielded less with conservation than with conventional tillage systems. Use of conservation tillage can improve or stabilize soil conditions in the region, but crop nutrient requirements must be met to achieve optimum crop yields when conservation tillage is used. Research regarding the plant nutrient requirements under conservation tillage is being conducted. Also, conservation tillage is gaining acceptance in the Argentinean Pampas region.
This study was carried out at a site (fine silty, Argiaquic Argialboll) in Illinois, USA, where use of no-tillage (NT) practices for over a decade had not increased soil organic carbon (SOC) sequestration relative to plots that had been mouldboard ploughed (MP). Even though the total SOC contents of these soils were known to be similar, input and decay rates of residue-derived C, conservation of root-derived C, and the importance of aggregate protection of particulate organic matter (POM) were expected to differ among these tillage treatments. Maize was pulse-labelled with 13CO2 repeatedly during the 1995 growing season to allow the fate of residue-derived C retained in loose-POM (LPOM), aggregate-occluded POM (OPOM) and in mineral associated humified (HF) fractions, to be tracked through April 1997. Tillage practices were related to fundamental differences in the depth and rate at which residues decayed and the distribution of those residues among SOC fractions. In December 1995, ~50% of the C derived from labelled residues was recovered in the LPOM, OPOM, and HF fractions of the NT plots, while only 22% was recovered in those fractions from MP plots. After initial rapid losses of label-derived C, C turnover rates were relatively slow in the MP plots compared to C turnover rates observed at the surface of the NT plots. As a result, after 1.5 years the MP and the NT plots retained similar amounts (~10%) of label-derived C in the 0-20 cm depth. Shifts in the percent label recovery suggest that newly assimilated C was rapidly lost from the LPOM fraction as it accumulated in the OPOM and HF fractions. Increases in the fractional abundance of label-derived C in the OPOM and HF fractions accounted for approx. half of the label lost from LPOM. Trends in both the fractional abundance and percentage label recovery in the OPOM and HF fractions indicated that C derived from 1995-residues was concentrated at 0-5 cm depth in NT plots and was more evenly distributed in the MP plots. In December 1995, the fractional abundance of OPOM and HF was greater in the root than shoot labelled plots, indicating that root-derived C was incorporated into SOC more rapidly than shoot-derived materials. By spring, the fractional abundance of OPOM and HF had increased in tilled plots amended with labelled shoots. The fractionation scheme showed the influence of aggregation on the decay dynamics of C introduced by newly incorporated residues and identified fundamental differences in the depth, decay dynamics and distribution of C, newly assimilated into the SOC fractions of NT and MP soils.
The water-stability of aggregates in many soils is shown to depend on organic materials. The organic binding agents have been classified into (a) transient, mainly polysaccharides, (b), temporary, roots and fungal hyphae, and (c) persistent, resistant aromatic components associated with polyvalent metal cations, and strongly sorbed polymers. The effectiveness of various binding agents at different stages in the structural organization of aggregates is described and forms the basis of a model which illustrates the architecture of an aggregate. Roots and hyphae stabilize macro-aggregates, defined as > 250 μm diameter; consequently, macroaggregation is controlled by soil management (i.e. crop rotations), as management influences the growth of plant roots, and the oxidation of organic carbon. The water-stability of micro-aggregates depends on the persistent organic binding agents and appears to be a characteristic of the soil, independent of management.
It is generally accepted that particulate organic matter derives from plants. In contrast, the enriched labile fraction is thought by many to derive from microbes, especially fungi. However, no detailed chemical characterization of these fractions has been done. In this study, we wanted to assess the sources (plants or microbes; fungi or bacteria) and degree of microbial alteration of (i) three particulate organic matter fractions – namely the free light fraction (1.85 g cm−3), the coarse (250–2000 μm) and the fine (53–250 μm) intra-aggregate particulate organic matter fractions – and of (ii) three density fractions of fine-silt associated carbon – namely < 2.0, 2.0–2.2 (i.e. enriched labile fraction) and > 2.2 g cm−3– by analysing the amino sugars, by CuO oxidation analyses, and by 13C-, 1H- and 31P-NMR analyses. Macroaggregates (250–2000 μm) were separated by wet-sieving from a former grassland soil now under a no-tillage arable regime. The three particulate organic matter fractions and the three density fractions were isolated from the macroaggregates by a combination of density flotation, sonication and sieving techniques. Proton NMR spectroscopy on alkaline extracts showed that the enriched labile fraction is not of microbial origin but is strongly degraded plant material that is enriched in aliphatic moieties partly bound to aromatics. In addition, the enriched labile fraction had a glucosamine content less than the whole soil, indicating that it is not enriched in carbon derived from fungi. Decreasing yields of phenolic CuO oxidation products and increasing side-chain oxidation in the order coarse intra-aggregate particulate organic matter < fine inter-aggregate particulate organic matter < fine-silt fractions indicate progressive alteration of lignin as particle size decreases. The light fraction was more decomposed than the coarse inter-aggregate particulate organic matter, as indicated by (i) its larger ratio of acid-to-aldehyde of the vanillyl units released by CuO oxidation, (ii) the smaller contribution of H in carbohydrates to total extractable H as estimated by 1H-NMR spectroscopy, and (iii) a larger contribution of monoester P to total extractable P in the 31P-NMR spectra. In conclusion, the four fractions are derived predominantly from plants, but microbial alteration increased as follows: coarse inter-aggregate particulate organic matter < light fraction ≈ fine inter-aggregate particulate organic matter < enriched labile fraction.
Effect of 19 years of different tillage (direct drilled vs. conventional tillage) and stubble management (stubble retained vs. burnt) on soil carbon fractions were studied in a red earth, an Oxic Paleustalf at Wagga Wagga, NSW. The changes in carbon fractions were related to observed changes in soil structural stability and nitrogen availability. Significant differences in total organic carbon (TOC) were detected to 0.20 m depth, but the largest differences existed in the top 0.05 m where a difference of 8.0 g/kg (equivalent to 5.2 t ha−1) was found between the extreme treatments (direct drilled/stubble retained (DD/SR) vs. conventional cultivation/stubble burnt (CC/SB)). Tillage had a much greater effect in reducing total carbon than stubble burning accounting for 80% of the total difference between the extreme treatments in 0–0.05 m layer. Tillage and stubble burning resulted in lower levels of different organic carbon fractions with tillage preferentially reducing the particulate organic carbon (POC) (>53 μm) (both free and associated POCs), whereas stubble burning reduced the incorporated organic carbon (<53 μm). We also found that tillage and stubble burning both significantly lowered the water stability of aggregate >2 mm, whereas stubble burning was related to the reduction of water stability of aggregates <50 μm. Furthermore, tillage was related to the decline in mineralisable nitrogen (MN) due to the loss of POC, especially the free POC fraction. POC was a more sensitive indicator of soil quality changes under different tillage and stubble management than TOC.
Changes in management practice are reflected by soil carbon and nitrogen status, in particular by the proportion of soil organic matter (SOM) being easily transformed (active SOM). We describe SOM quality for three management practices, Organic Farming system (OF), Integrated Crop Production (ICP) and pasture sites (G), which intend to achieve sustainable management practice. The experimental sites were conventionally farmed until 1992. SOM quality was examined by describing active SOM pools, such as the decomposed ‘young soil organic matter’ (YSOM), ratio of microbial biomass carbon (Cmic) to organic carbon (Corg), ecophysiological status of the microbial biomass (qCO2), and the ratio of light particulate organic matter (POM-LF) to Corg. Ratios of soil microbial biomass (Cmic/Corg) and POM-LF (POM-LF/Corg) and the amount of decomposed YSOM were relatively similar to each other, despite differences in management practice and soil texture. Soil microbial parameters (Cmic, Cmic/Corg and qCO2) were significantly (p<0.05) affected by the amount of decomposed YSOM and the silt content in the OF. In the ICP, soil microbial parameters depended only on the amount of decomposed YSOM, which was considered to be a consequence of the more heterogeneous texture at the OF-sites. Management effects were detectable for no-tillage in the ICP leading to an accumulation of active SOM in the surface soil (0–10 cm). The ratio POM-LF/Corg showed no difference between G and OF despite markedly higher Corg-contents at the G-sites. Conclusively, all methods used indicate comparable SOM qualities for the three management systems, despite differences in soil texture and soil management during 7 years. Management practices seem to be well adapted to the site conditions.
The concept and some definitions of sustainable agriculture are reviewed. Most of these definitions include economic, environmental and sociological aspects. The finite area of land emphasizes the need for consideration of soil conservation and of soil quality in relation to sustainability. An important element of soil quality is rooting depth. Therefore loss of soil by erosion is a dominant factor in long-term sustainability. The effects of tillage on soil parameters in minimum data sets that have been proposed to describe soil quality are reviewed. Soil organic matter may be one of the most important soil quality characteristics in relation to tillage because of its influence on other soil physical, chemical and biological properties. Conservation tillage practices can increase the organic matter content, aggregate stability and cation exchange capacity (CEC) of the topsoil. However, bulk density and penetrometer resistance are also increased, especially with zero tillage. Although such soil quality parameters may form a basis for describing some of the consequences of particular tillage practices, they do not provide a basis for predicting the outcome in terms of crop growth and yield. This is both because critical values of soil quality parameters have not been defined and because in some soils biopore formation in zero or minimally tilled land can modify the soil for water movement and for root growth and function.
Under semiarid Mediterranean climatic conditions, soils typically have low organic matter content and weak structure resulting in low infiltration rates. Aggregate stability is a quality indicator directly related to soil organic matter, which can be redistributed within soil by tillage. Long-term effects (1983–1996) of tillage systems on water stability of pre-wetted and air dried aggregates, soil organic carbon (SOC) stratification and crop production were studied in a Vertic Luvisol with a loam texture. Tillage treatments included conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) under winter wheat (Triticum aestivum L.) and vetch (Vicia sativa L.) rotation (W–V), and under continuous monoculture of winter wheat or winter barley (Hordeum vulgare L.) (CM). Aggregate stability of soil at a depth of 0–5 cm was much greater when 1–2 mm aggregates were vacuum wetted prior to sieving (83%) than when slaked (6%). However, slaking resulted in tillage effects that were consistent with changes in SOC. Aggregate stability of slaked aggregates was greater under ZT than under CT or MT in both crop rotations (i.e., 11% vs. 3%, respectively).
A multi-year experiment was conducted to compare the effects of conservation tillage (no-till and ridge-till) with conventional plow tillage on organic C, N, and resin-extractable P in an alkaline semi-arid subtropical soil (Hidalgo sandy clay loam, a fine-loamy, mixed, hyperthermic Typic Calciustoll) at Weslaco, TX (26°9′N 97°57′W). Tillage comparisons were established on irrigated plots in 1992 as a randomized block design with four replications. Soil samples were collected for analyses 1 month before cotton planting of the eighth year of annual cotton (planted in March) followed by corn (planted in August).No-till resulted in significantly (p<0.01) greater soil organic C in the top 4 cm of soil, where the organic C concentration was 58% greater than in the top 4 cm of the plow-till treatment. In the 4–8 cm depth, organic C was 15% greater than the plow-till control. The differences were relatively modest, but consistent with organic C gains observed in hot climates where conservation tillage has been adopted. Higher concentrations of total soil N occurred in the same treatments, however a significant (p<0.01) reduction in N was detected below 12 cm in the ridge-till treatment. The relatively low amount of readily oxidizable C (ROC) in all tillage treatments suggests that much of the soil organic C gained is humic in nature which would be expected to improve C sequestration in this soil.Against the background of improved soil organic C and N, bicarbonate extractable P was greater in the top 8 cm of soil. Some of the improvement, however, appeared to come from a redistribution or “mining” of P at lower soil depths. The results indicate that stratification and redistribution of nutrients were consistent with known effects of tillage modification and that slow improvements in soil fertility are being realized.
Soil compactibility which basically depends on soil texture, organic matter and soil water content during farm machinery trafficking are major factors affecting soil conservation. In a field experiment, cattle farmyard manure was applied to a silty clay loam soil (fine-loamy, mixed, thermic Typic Haplargids, USDA; Calcaric Cambisols, FAO) in Isfahan, Iran. Three rates, 0, 50, 100 Mg ha−1 (on oven dry basis) of farmyard manure, were incorporated into the topsoil. After 5 months, a two-wheel drive tractor (48.5 kW) was passed over the plots once (P1) or twice (P2) at soil moisture contents associated with the plastic limit (PL), 0.8PL, and 0.6PL. A randomized complete block design with four replicates with treatments nested (split-block) into the blocks was used. Bulk density (BD), cone index (CI) and soil sinkage were measured as indices of soil compactibility and trafficability. Applying 50 and 100 Mg ha−1 of manure significantly counteracted the effects of load and wetness on BD and CI. There was a significant difference between the effects of 50 and 100 Mg ha−1 of manure on BD, but not on CI. Manure application also reduced the subsoil compaction. Double passes of the tractor (P2) significantly increased compaction. There was a limitation for trafficability for no-manure treatment even at 0.6PL, whereas this limit was reached at 0.8PL for the 50 Mg ha−1 treatment. Results from this study demonstrate that manure application at a rate of 50 Mg ha−1 reduced soil compactibility and increased soil moisture trafficability range. Thus, increasing soil organic matter could bring about an appropriate solution for sustainable soil management in the region.
The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA1: fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0–7.5, 7.5–15, and 15–30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop–fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mg ha−1), particulate organic matter C (POM-C) (by 4.98 Mg ha−1), potentially mineralizable N (PMN) (by 32.4 kg ha−1), and microbial biomass C (by 586 kg ha−1), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h−1) relative to the crop–fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha−1 for PMN; 792 kg ha−1 for microbial biomass C) as compared with sequences with fallow (SW–S–F and SW–F) (Average=15.9 kg ha−1 for PMN; 577 kg ha−1 for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.
Minimum tillage practices are known for increasing soil organic carbon (SOC). However, not all environmental situations may manifest this potential change. The SOC and N stocks were assessed on a Mollisol in central Ohio in an 8-year-old tillage experiment as well as under two relatively undisturbed land uses; a secondary forest and a pasture on the same soil type. Cropped systems had 51±4 (equiv. mass) Mg ha−1 lower SOC and lower 3.5±0.3 (equiv. mass) Mg ha−1 N in the top 30 cm soil layer than under forest. Being a secondary forest, the loss in SOC and N stocks by cultivation may have been even more than these reported herein. No differences among systems were detected below this depth. The SOC stock in the pasture treatment was 29±3 Mg ha−1 greater in the top 10 cm layer than in cultivated soils, but was similar to those under forest and no-till (NT). Among tillage practices (plow, chisel and NT) only the 0–5 cm soil layer under NT exhibited higher SOC and N concentrations. An analysis of the literature of NT effect on SOC stocks, using meta-analysis, suggested that NT would have an overall positive effect on SOC sequestration rate but with a greater variability of what was previously reported. The average sequestration rate of NT was 330 kg SOC ha−1 year−1 with a 95% confidence interval ranging from 47 to 620 kg SOC ha−1 year−1. There was no effect of soil texture or crop rotation on the SOC sequestration rate that could explain this variability. The conversion factor for SOC stock changes from plow to NT was equal to 1.04. This suggests that the complex mechanisms and pathways of SOC accrual warrant a cautious approach when generalizing the beneficial changes of NT on SOC stocks.
The effects of agricultural land use on organic matter content and related soil microbial and physical properties were compared with those under undisturbed native grassland in KwaZulu-Natal, South Africa. Two separate farms situated on Oxisols were used and both contained fields with continuous long-term (>20 y) cropping histories. At site 1, soil organic C content in the surface 30 cm followed the order permanent kikuyu pasture > annual ryegrass pasture > native grassland > sugarcane > maize under conventional tillage (CT). At site 2, organic C in the surface 30 cm decreased in the order kikuyu pasture > native grassland > annual ryegrass pasture > maize under zero tillage (ZT) greater than or equal to maize CT. Organic C, microbial biomass C, percentage organic C present as organic C, basal respiration and aggregate stability were substantially greater in the surface 5 cm under maize ZT than maize CT but this trend tended to be reversed in the 10- to 30-cm layer. In the undisturbed sites (e.g. native grassland and kikuyu pasture) the metabolic quotient increased with depth. By contrast, under maize CT and sugarcane there was no significant stratification of organic C, yet there was a sharp decrease in the metabolic quotient with depth. Aggregate stability was high under both native grassland and kikuyu pasture and it remained high to 40 cm depth under the deep-rooted kikuyu pasture. Although soil organic C content was similar under maize CT and sugarcane, values for microbial biomass C, percentage of organic present as microbial biomass, basal respiration and aggregate stability were lower, and those for metabolic quotient and bulk density were higher, under sugarcane. This was attributed to the fallow nature of the soil in the interrows of sugarcane fields. It was concluded that the loss of organic matter, microbial activity and aggregate stability is potentially problematic under maize CT, sugarcane and annual pasture and measures that improve organic matter status should be considered.
Dryland crop production is limited by precipitation and by soil factors such as texture and profile depth-that affect water storage capacity, pH, fertility, and salinity. When prevailing precipitation and soil factors are not in balance, crops will not yield at their potential and productivity may be impaired because soil degradation processes outweigh conservation practices. Sustainable crop production is possible through use of appropriate tillage and crop residue management practices. When adequate crop residues are available, conservation tillage is highly effective for conserving soil and water, achieving favorable crop yields, maintaining soil organic carbon contents, and soil and water quality. Other tillage methods along with appropriate conservation practices may be needed when crop residues are limited.
Soil C and N have long been recognized as important indicators of soil productivity. The current low levels of soil C and N of cropland soils have led to interest in sequestering C with reduced tillage cropping systems and the Conservation Reserve Program (CRP). Our objective was to assess agroecosystem effects on soil C and N pools in the Southern High Plains. The agroecosystems included three cotton (Gossypium hirsutum L.) cropping systems, CRP land, and native rangeland (NR). We sampled 0- to 5-, 5- to 10-, 10- to 15-, and 15- to 30-cm soil depths at 12 farm sites in five counties in West Texas. Total soil C and N, particulate organic matter (POM) C and N, natural abundance of carbon-13 isotope (delta13C) of POM and of whole soil, potentially mineralizable C and N, water-extractable carbon (WEC), and extractable ammonium (NH+4) and nitrate (NO-3) were determined. Total C and N in the 0- to 30-cm soil profile were 34 Mg C ha-1 and 2.5 Mg N ha-1 for NR, and 23 Mg C ha-1 and 1.9 Mg N ha-1 for cropland systems, respectively. Total soil C and N in CRP land were greater in cropland soils only in the 0- to 5-cm layer, and were 24 Mg C ha-1 and 2.1 Mg N ha-1 in 0 to 30 cm. Labile C and N pools were positively correlated with each other and with total soil C and N. Low soil test P may have limited C and N sequestration in CRP land and NR. Improved management practices are needed to sequester C and N in CRP and conservation-tillage cotton systems in the Southern High Plains.
Particulate organic matter nitrogen (POM-N) was evaluated as an indicator of crop residue source ( pulse versus cereal) and residue management (no-tillage [NT], stubble burned [SB] or stubble mulched [SM]) on soil quality and subsequent crop productivity in a continuous cropping experiment in northern New South Wales ( NSW), Australia. The relative contributions to POM of pulse versus cereal, and shoots versus roots, were studied using in situ N-15 shoot labelling. Under NT, a greater proportion of organic N was found in POM-N > 250 mum (5.5% versus 3.5% [SM] and 2.7% [SB]) and POM-N > 53 mum (10.3% versus 9.7% [SM] and 8.7% [SB]). Pulse residues ( particularly roots) contributed 2-7 times more N to POM and 20-4 times more N to non-POM-N than barley (N-15 data), but this increased contribution was not detectable with non-isotopic analysis. POM-N was sensitive to residue management, but was not a reliable measure of N inputs from pulse versus cereal residues, nor a useful tool for predicting subsequent crop N uptake.
The negative health effects of repeated dust exposure have been well documented. In California's San Joaquin Valley, agricultural operations may contribute substantially to airborne particulates. We evaluated four management systems to assess impacts on dust production and soil properties for a cotton (Gossypium hirsutum L.)-tomato (Lycopersicon esculentum Mill.) rotation: standard tillage with (STCC) and without (STNO) cover crop, and conservation tillage with (CTCC) and without (CTNO) cover crop. Gravimetric analysis of total dust (TD, <100-mum aerodynamic diameter) and respirable dust (RD, 4-mum aerodynamic diameter) samples collected in the plume generated by field implements showed that dust concentrations for CTNO treatments were about one-third of their STNO counterparts for both cumulative TD and RD measured throughout the two-year rotation, primarily due to fewer in-field operations. The TD and RD production for STNO and STCC was comparable, whereas the CTCC system produced about twice as much TD and RD as CTNO. Energy dispersive spectroscopy (EDS) analyses showed absolute increases of 8 and 39% organic fragments in STCC and CTCC over STNO and CTNO, respectively, while organic fragments in the TD increased by 6% in both cover crop treatments. Soil C content was positively correlated with clay content and increased by an average of 0.12 and 0.07% in the cover crop and non-cover crop treatments, respectively, although soil C for each treatment showed a distinct response to a field texture gradient. While dust emissions show an immediate decrease due to fewer field operations for the conservation tillage treatments, long-term sampling is necessary to determine the effects that increased aggregation through organic matter additions may have on dust production.
- Rees
Cotton production manual University of California Division of Agriculture and Natural Resources Oakland CA
- S J Hake
- T A Kerby
Interaction of tillage and soil texture: Biologically active soil organic matter in Illinois
- Needelman
- Rees R.M.