Content uploaded by María Alonso-Ayuso
Author content
All content in this area was uploaded by María Alonso-Ayuso on Feb 03, 2020
Content may be subject to copyright.
A preview of the PDF is not available
Weed density and diversity in a long-term cover crop experiment background
Abstract and Figures
Cover crops (CC) are biological tools with a great potential for weed control, but the suppression level depends on the CC species and management. A 2-year study was performed in the eighth year of a long-term experiment located in Central Spain to study the effect of replacing winter fallow by barley (Hordeum vulgare L.) or vetch (Vicia sativa L.), on the weed control. Moreover, two CC termination dates were evaluated. Weed biomass, density, diversity, population composition and the seed bank were assessed. Ground cover and CC biomass, soil inorganic N and topsoil water content were determined throughout the season. Barley achieved a greater weed control compared to vetch in winter and early spring. Later in May, both CC residues decreased weed density compared to fallow (63% in 2015, 55% in 2016), and reduced the density of some broadleaf species (i.e. Xanthium spinosum L. reduced >50%). The weed seedbank density was not affected by CC but the effect on specific species confirmed the control over Xanthium spp. (78% reduction), and also warned of the incomplete weed control by CC. The year in which the biomass and ground cover increased between termination dates, delaying the CC termination reduced weed density >75%. Therefore, delaying the termination date was a mean to increase weed control but should be performed with caution to avoid pre-emptive competition with the cash crop. Results underline the relevance of CC species and the termination date as management tools for weed control, and must be considered to plan specific management strategies in different scenarios.
Figures - uploaded by María Alonso-Ayuso
Author content
All figure content in this area was uploaded by María Alonso-Ayuso
Content may be subject to copyright.
... In the future, large-scale implementation is needed to support the transition towards green, year-round soil cover and achieve the numerous ecosystem services that CCs may provide [1]. The potential advantages for crop production include higher yields [2,3], nutrient cycling [4,5], weed control [6,7], improved soil health [8][9][10], and adaptation to climate change [11]. On the other hand, ecosystem services provided by CCs include reduced nutrient leaching and erosion [12,13], pesticide acquisition [14], and carbon sequestration [15,16]. ...
... Organic and conventional farmers differed in terms of their rationales for the cultivation of CCs: organic farmers especially valued multifunctionality and various ecosystem services from CCs [44]. Farmers use CCs to increase soil health, decrease soil disturbance, control weeds, and improve nutrient cycling [5,6,8,9,20,45] and, thereby, promote crop yields [2]. Organic farmers usually had more experience with CCs than conventional farmers. ...
... The difference between farming systems was most striking in how successful farmers were in controlling weeds with CCs ( Figure 4). In organic production, CCs act as an important biological tool, but their weed suppression capacity varies depending on the properties of the CCs, as well as the conditions and used crop management [6,7,[52][53][54]. Successes with CCs did not greatly differ depending on the farm size-nor in terms of controlling weeds-but farmers with larger farms agreed more frequently that they considered the means to increase success with CCs a lot ( Figure 5). ...
In Finland, there is an ongoing adoption and learning process considering the cultivation of cover crops (CCs). The primary aim is to claim the benefits of CCs for agricultural production and ecosystems, which are both appreciated by Finnish farmers. A farmer survey with 1130 respondents was carried out to build an up-to-date understanding of how farmers have succeeded with CCs and whether they intend to continue with the use of CCs and to collect farmers’ views on knowledge gaps that should be filled by research or better knowledge sharing. The studied groups were farmers who had selected CCs as a registered measure in 2020 to receive agricultural payments. Data came from the Finnish Food Authority. Organic farmers were slightly more positive: they have had longer experience with CCs, but organic production is also more dependent on the ecosystem services provided by CCs. A high share of respondents agreed that their experiences with CCs have improved over time and were confident that CCs had become a permanent element of their production systems. Most of the farmers also agreed that the area under CCs would expand significantly in Finland and considered the cultivation of CCs as an effective measure to improve soil conditions. They often considered that challenges in adopting CCs were exaggerated and disagreed that bad experiences prevented them from expanding or continuing the use of CCs. The agricultural payment available for Finnish farmers to support the cultivation of CCs is quite reasonable (EUR 97 + EUR 50 per hectare) to compensate for any economic risks of CCs. Free word answers from the farmers highlighted research needs (in descending order) in the following areas: crop protection, sowing practices, the use of diverse CCs and their mixtures, and impacts on yield and profitability. Many of these are universal, i.e., have been reported elsewhere. Younger farmers (≤50 years) highlighted profitability, which is, in many European countries, a key barrier to the deployment of CCs. Farmers from the east and north regions, where the growing season is short, highlighted alternative CC choices as a knowledge gap.
... Previous studies investigating the effect of CC on weed seedbanks have reported contrasting results (Moonen and Barberi, 2004;Mirsky et al., 2010;Alonso-Ayuso et al., 2018). Moreover, the majority of relevant studies were conducted in plots where CC treatments were implemented less than 3 years and hence, provided little information on the long-term effect of CC on weed seedbanks. ...
... For example, the difference between CC was striking during the 2012 cover cropping period, when the highly productive brown mustard showed no effect on percentage cover of Poa annua, whereas hairy vetch nearly filtered out the species. CC:weed specific responses have been reported in many studies, yet the mechanisms at play remain to be identified (Moonen and Barberi, 2004;Alonso-Ayuso et al., 2018;Rouge et al., 2022). Similarly, Nichols et al. (2020) found no relation between CC productivity or stability and weed seedbank abundance. ...
Context: Little is known about the long-term contribution of cover crops to weed management in tillage-and herbicide-based systems. Research questions: Do cover crops mainly filter weed species capable of setting seeds during the fallow period? Can cover crop biomass productivity explain differences in weed suppression among cover crop species? Does reduced weed seedbank density translate into lower weed biomass and higher crop productivity? Methods: Soil samples (0-15 cm) were collected in 2018 after cover crop termination and used in a greenhouse seedling emergence assay to assess the topsoil weed seedbank capable of germinating 25 years after the beginning of a split-plot experiment on tillage systems (conventional vs. reduced) and cover crops (bare soil control, Brassica juncea (brown mustard), and Vicia villosa (hairy vetch)). Total density and density of the 10 most abundant weed species in the topsoil seedbank were related to observations of weed species visual soil cover, total weed biomass, cover crop biomass, and cash crop grain yield made during the six years which preceded the weed seedbank assessment. Weed seedling density was also used to compute community weighted mean of germination and flowering period. Results: In comparison with the bare soil control, hairy vetch suppressed total weed seedling density by 40%, whereas brown mustard showed no effect. In comparison with the bare soil control, hairy vetch suppressed weed seedling density of Cerastium glomeratum (− 87%), Veronica persica (− 86%), Capsella bursa-pastoris (− 57%) and Poa annua (− 42%), whereas brown mustard only suppressed C. bursa-pastoris (− 65%) and V. persica (− 49%). The suppressive effect of hairy vetch on these four species translated into a significant reduction of community weighted mean of autumn/winter germination period and March to July flowering period. The contrasted suppressive effect of brown mustard and hairy vetch on weed seedling density of these four species was related to contrasted competitive interactions during the four previous cover crop seasons. However, differences in weed suppression between hairy vetch and brown mustard could not be fully explained by differences in biomass productivity. Management intensity (e.g. herbicides and tillage) potentially smoothed out differences in weed suppression between cover crop treatments because no effect of cover crops were observed on total weed biomass or gain yield of the subsequent crops over the 2012-2017 period. Conclusion: Cover crops contribute little to weed management in herbicide and tillage-based cropping systems. Implication: The weed suppressive effect of cover crops should be further explored in cropping systems which minimise herbicide use and tillage intensity.
... However, identifying the mechanisms by which cover crops exert their negative effects on weeds in the field remains challenging [24], but crucial to improve their efficacy. Cover crops have proven to be an effective ecological-based weed management tool in various agricultural systems [25][26][27][28]. Cover cropping is one of the main pillars of weed management in no-till and conservation agricultural systems [29]. ...
Cover crops, as either a living plant or mulch, can suppress weeds by reducing weed germination, emergence and growth, either through direct competition for resources, allelopathy, or by providing a physical barrier to emergence. Farmers implementing conservation agriculture, organic farming, or agroecological principles are increasingly adopting cover crops as part of their farming strategy. However, cover crop adoption remains limited by poor and/or unstable establishment in dry conditions, the weediness of cover crop volunteers as subsequent cash crops, and seed costs. This study is the first to review the scientific literature on seed traits of cover crops to identify the key biotic and abiotic factors influencing germination and early establishment (density, biomass, cover). Knowledge about seed traits would be helpful in choosing suitable cover crop species and/or mixtures adapted to specific environments. Such information is crucial to improve cover crops' establishment and growth and the provision of ecosystem services, while allowing farmers to save seeds and therefore money. We discuss how to improve cover crop establishment by seed priming and coating, and appropriate seed sowing patterns and depth. Here, three cover crop families, namely, Poaceae, Brassicaceae, and Fabaceae, were examined in terms of seed traits and response to environmental conditions. The review showed that seed traits related to germination are crucial as they affect the germination timing and establishment of the cover crop, and consequently soil coverage uniformity, factors that directly relate to their suppressive effect on weeds. Poaceae and Brassicaceae exhibit a higher germination percentage than Fabaceae under water deficit conditions. The seed dormancy of some Fabaceae species/cultivars limits their agricultural use as cover crops because the domestication of some wild ecotypes is not complete. Understanding the genetic and environmental regulation of seed dormancy is necessary. The appropriate selection of cover crop cultivars is crucial to improve cover crop establishment and provide multiple ecosystem services, including weed suppression, particularly in a climate change context.
... However, identifying the mechanisms by which cover crops exert their negative effects on weeds in the field remain challenging [24] but is crucial to improve their efficacy. Cover crops have proven to be an effective ecological-based weed management tool in various agricultural systems [25][26][27][28]. Cover cropping is one of the main pillars of weed management in no-till and conservation agriculture systems [31]. ...
Cover crops as living plant or mulch can suppress weeds by reducing weed germination, emergence and growth, either through direct competition for resources, allelopathy, or by providing a physical barrier to emergence. Farmers implementing conservation agriculture, organic farming or agroecological principles are increasingly adopting cover crop as part of their farming strategy. However, cover crop adoption remains limited by poor and/or unstable establishment in dry conditions, weediness of cover crop volunteers is subsequent cash crops, and seed cost. This study is the first one to review the literature on seed traits of cover crops, their germination response to different biotic and abiotic factors aiming to improve seed germination and seedling establishment. Knowledge on seed traits would be helpful in choosing suitable cover crop species and/or mixture adapted to specific environments. Such information is crucial to improve cover crops establishment, growth, provision of ecosystem services, while allowing farmers to save seeds and therefore money. We discuss how to improve cover crop establishment by seed priming and coating, and appropriate seed sowing depth. Here, three cover crop families namely Poaceae, Brassicaceae, and Fabaceae, were examined in terms of seed traits and response to environmental conditions. The review showed that seed traits related to germination are crucial as they affect the germination timing and establishment of the cover crop, consequently soil coverage uniformity, factors that directly related to their suppressive effect on weeds. Poaceae and Brassicaceae exhibit higher germination percentage than Fabaceae under water deficit conditions. Seed dormancy of some Fabaceae species/cultivars limits their agricultural use of as cover crops because the domestication of some wild ecotypes is not complete. Understanding genetic and environmental regulating seed dormancy is necessary. Appropriate selection of cover crop cultivars is crucial to improve cover crop establishment and provide multiple ecosystem services including weed suppression, particularly in a climate change context.
... It was agreed by 57% of respondents that the sowing time determines whether CCs compete with the cash crop ( Figure 1). This may happen especially in the case of failures with cash crop sowing and establishment [32], e.g., due to harmful weather events [16], poorly germinating farm-saved seeds [33] or use of an aggressively growing CC-species like sweet clover [14]. ...
Farmers may promote the cultivation of under-sown cover crops (CCs) in various ways without jeopardizing the yield of a cash crop. With this survey, we aimed to understand how Finnish farmers manage possible challenges with under-sown CCs. A farmer survey was carried out in 2021. We invited 6493 farmers who had selected CCs as a registered measure to answer a questionnaire with 20 statements (a Likert scale), and 1130 responded (17.4%). A Cochran–Mantel–Haenszel test was used to measure the strength of the association between 11 farm/farmer characteristics of the respondents and 20 statements. Responses indicated that farmers often took under-sown CCs into account during the growing season. Sowing was considered an especially critical measure and the CC seeding rate was often assessed with a test run before sowing. Thirty-nine per cent of the respondents had made investments, most often to facilitate sowing. The farmers usually adjusted the fertilizer rate only according to the cash crop. Early harvesting of a cash crop was considered important by 58% of farmers to ensure that the CCs do not hamper the harvest. Farmers harvested cash crops as soon as they matured and were harvestable, though they had mixed views on whether CCs impacted the quality of the cash crop. Subsidized, investing farmers were likely to be oriented towards the benefits from the ecosystem services provided by CCs. Their experiences should be shared among the farming community to support the large-scale implementation of CCs.
... It also discourages weed seed germination by producing allelopathic chemicals (chemicals that are toxic to other plants) (Jacobs, 2016). Barley cover crops can suppress weeds with annual lifecycles such as annual sowthistle (Sonchus oleraceus), barnyardgrass (Echinochloa crus-galli), common groundsel (Senecio vulgaris) and yellow foxtail (Setaria glauca) (Alonso-Ayuso et al., 2018;Creamer et al., 1996;Dhima et al., 2006), as well as weeds with perennial lifecycles including bermudagrass (Cynodon dactylon) (Valencia-Gredilla et al., 2020). Fall-sown barley cover crops generally outcompete winter weeds, resulting in very little weed biomass at the time of cover crop termination (Silva, 2014;Wayman et al., 2014), although weed suppression ability can differ among barley varieties (Christensen, 1995). ...
Adoption of cover crops in arid agroecosystems has been slow due to concerns regarding limited water resources and possible soil moisture depletion. In irrigated organic systems, potential ecosystem services from cover crops also must be considered in light of the concerns for water conservation. A constructive balance could be achieved with fall-sown small grain cover crops; however, their impacts on irrigated organic systems are poorly understood. Our first objective was to determine the ability of fall-sown small grains [cereal rye ( Secale cereale L), winter wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.) and oat ( Avena sativa L.)] to suppress winter weeds in an irrigated, organic transition field in the southwestern USA. Small grains were planted following the legume sesbania ( Sesbania exaltata (Raf.) Rydb. ex A.W. Hill) during Fall 2012 and Fall 2013. In Spring 2013 and 2014, weed densities and biomass were determined within each cover crop treatment and compared against unplanted controls. Results indicated that both barley and oat were effective in suppressing winter weeds. Our second objective was to compare weed suppression and soil moisture levels among seven barley varieties developed in the western United States. Barley varieties (‘Arivat’, ‘Hayes Beardless’, ‘P919’, ‘Robust’, ‘UC603’, ‘UC937’, ‘Washford Beardless’) were fall-sown in replicated strip plots in Fall 2016. Weed densities were measured in Spring 2017 and volumetric soil moisture near the soil surface (5.1 cm depth) was measured at time intervals beginning in December 2016 and ending in March 2017. With the exception of ‘UC937’, barley varieties caused marked reductions in weed density in comparison with the unplanted control. Soil moisture content for the unplanted control was consistently lower than soil moisture contents for barley plots. Barley variety did not influence volumetric soil moisture. During the 2017–2018 growing season, we re-examined three barley varieties considered most amenable to the cropping system requirements (‘Robust’, ‘UC603’, ‘P919’), and these varieties were again found to support few weeds (≤ 5.0 weeds m ⁻² ). We conclude that several organically certified barley varieties could fill the need for a ‘non-thirsty’ cover crop that suppresses winter weeds in irrigated organic systems in the southwestern United States.
Effective weed management faces increasing legislative restrictions for the use of herbicides due to their toxicity and environmental persistence. In addition, the linear increase in resistant weeds threatens to render authorized herbicides useless. In a post-herbicide era, under the IWM strategy, allelopathy can play a relevant role since many plants can produce a variety of allelochemicals with different structures and modes of action, capable of inhibiting the germination and growth of different weed species. Inspired by green manuring with cover crops, the use of allelopathic biomass from weeds, invasive species, residues of forestry plantations, and other abundant wild plants has some advantages over green manures grown in situ or other alternatives such as applying plant extracts or essential oils. Beyond the ecosystem services provided by green manures, the potential use of allelopathic biomass offers extra opportunities for the science and practice of holistically integrated weed management because (i) the investment of resources and time for producing cover crops would be alleviated, and (ii), new use of agroforestry residues and a sink for harmful weed biomass is provided. In this review, we compile the current knowledge of those allelopathic species whose biomass, used as soil amendment, effectively controlled weeds. In addition, the complex allelopathic processes underlying the effectiveness of cover crops and allelopathic biomass used as green manures for weed control are revisited.
Cover crops (CCs) can affect the cropping systems’ N dynamics and soil water content (SWC), but optimizing their potential effects requires knowledge of their growth pattern, N accumulation, and mineralization. For this purpose, a 3-year field experiment was initiated in northeast Italy involving a maize-soybean rotation. The objectives of this study were to (i) evaluate the use of time series vegetation indices (VIs) obtained from the Sentinel-2 satellite for monitoring the growth of CCs and estimating their biomass and N uptake at termination; (ii) investigate the effects of different CCs on cash crop yield and SWC; and (iii) use the simulation model CC-NCALC to predict the nitrogen contribution of CCs to subsequent cash crops. Three CC systems were tested: a fixed treatment with triticale; a 3-year succession of rye, crimson clover, and mustard; and a control with no CCs. Satellite imagery revealed that rye and triticale grew faster during the winter season than clover but slower compared to mustard, which suffered a frost winterkilling. Both grasses and mustard produced greater biomass at termination compared to clover, but none of the CC species affected SWC or yield and N uptake of the cash crop. A net N mineralization of all the CC residues was estimated by the model (except for the N immobilization after triticale roots residues). During the subsequent cash crop season, the estimated clover and mustard N released was around 33%, and the triticale around 3% of their total N uptake, with a release peak 2 months after their termination. The use of remote sensing imagery and a prediction model of CC residue decomposition showed potential to be used as instruments for optimizing the CCs utilization and enhancing cropping water and N fertilization management efficiency; however, it must be further analyzed with other CCs species, environmental conditions, and cropping systems.
Alkali barnyardgrass [ Echinochloa crus-galli var . zelayensis (H.B.K.) Hitchc] and junglerice [ Echinochloa colona (L.) Link] are problematic annual weeds in direct-seeded rice ( Oryza sativa L.) fields in China. The emergence ecology of the two weed species may differ in response to environmental factors. Laboratory and screenhouse experiments were conducted to evaluate the effects of light, burial depth, mulching with wheat ( Triticum aestivum L.) residue, and time and depth of flooding on the emergence of the two weed species collected from Nanjing, China. Light strongly increased seed germination. Under dark conditions, E. crus-galli seed germination (85%) was higher than that of E. colona (70%). The seeds of both species exhibited the greatest germination (90% for E. crus-galli and 80% for E . colona ) when sown on the soil surface, and emergence decreased with increasing soil burial depths. A burial depth of 2.2 and 1.4 cm reduced seedling emergence by 50% for E. crus-galli and E. colona , respectively. No emergence was found at a depth of 6 cm. The seedling emergence for E. colona was lower than for E. crus-galli at the same soil burial depth. Mulching with wheat residue considerably reduced the seedling emergence and aboveground biomass of both species. The inhibitory effect of mulching with wheat residue on E . colona was more notable than on E. crus-galli . Early and deep flooding significantly suppressed the emergence, height, and biomass of E. crus-galli and E. colona , especially E . colona . The results gained from this study could provide fundamental ecological knowledge for managing Echinochloa species in direct-seeded rice systems.
Crop residues on the soil surface protect the soil against erosion, increase water infiltration and reduce agrochemicals in runoff water. Crop residues and soils are spectrally different in the absorption features associated with cellulose and lignin. Our objectives were to: (1) assess the impact of water on the spectral indices for estimating crop residue cover (fR); (2) evaluate spectral water indices for estimating the relative water content (RWC) of crop residues and soils; and (3) propose methods that mitigate the uncertainty caused by variable moisture conditions on estimates of fR. Reflectance spectra of diverse crops and soils were acquired in the laboratory over the 400–2400-nm wavelength region. Using the laboratory data, a linear mixture model simulated the reflectance of scenes with various fR and levels of RWC. Additional reflectance spectra were acquired over agricultural fields with a wide range of crop residue covers and scene moisture conditions. Spectral indices for estimating crop residue cover that were evaluated in this study included the Normalized Difference Tillage Index (NDTI), the Shortwave Infrared Normalized Difference Residue Index (SINDRI) and the Cellulose Absorption Index (CAI). Multivariate linear models that used pairs of spectral indices—one for RWC and one for fR—significantly improved estimates of fR using CAI and SINDRI. For NDTI to reliably assess fR, scene RWC should be relatively dry (RWC < 0.25). These techniques provide the tools needed to monitor the spatial and temporal changes in crop residue cover and help determine where additional conservation practices may be required.
Cover crops represent a potentially important biological filter during weed community assembly in agroecosystems. This filtering could be considered directional if different cover-crop species result in weed communities with predictably different species composition. We examined the following four questions related to the potential filtering effects of cover crops in a field experiment involving five cover crops grown in monoculture and mixture: (1) Do cover crops differ in their effect on weed community composition? (2) Is competition more intense between cover crops and weeds that are in the same family or functional group? (3) Is competition more intense across weed functional types in a cover-crop mixture compared with cover crops grown in monocultures? (4) Within a cover-crop mixture, is a higher seeding rate associated with more effective biotic filtering of the weed community? We found some evidence that cover crops differentially filtered weed communities and that at least some of these filtering effects were due to differential biomass production across cover-crop species. Monocultures of buckwheat and sorghum-sudangrass reduced the number of weed species relative to the no-cover-crop control by an average of 36 and 59% (buckwheat) and 25 and 40% (sorghum-sudangrass) in 2011 and 2012, respectively. We found little evidence that competition intensity was dependent upon the family or functional classification of the cover crop or weeds, or that cover-crop mixtures were stronger assembly filters than the most effective monocultures. Although our results do not suggest that annual cover crops exert strong directional filtering during weed community assembly, our methodological framework for detecting such effects could be applied to similar future studies that incorporate a greater number of cover-crop species and are conducted under a greater range of cover-cropping conditions.
Overwintered cover crops mechanically terminated into mulch can be a weed management tool for reduced-tillage organic agriculture. However, the impacts of management options for cover cropping are not well understood, including cover crop variety, termination timing and termination method. In a field experiment, conducted in 2012 and 2013 in Western Washington, we examined three grains, four vetches and one barley–vetch mix terminated with two mechanical methods and at two different times. We determined the influence of cover crop variety and termination time on cover crop biomass production and tissue nitrogen (N), effectiveness of cover crop termination, soil nitrate–N and percent weed cover. We also determined the influence of termination method on percent weed cover. Cover crop biomass ranged between 3 and 9 Mg ha
−1
and was not influenced by termination time; the greatest production was from three varieties of grain. Rye varieties were more effectively terminated with a roller–crimper than barley. Mean soil nitrate–N levels ranged from 1.9 to 18 mg kg
−1
and were the greatest with vetches. Post-termination weed cover was greater in 2013 than in 2012 and the cover crop variety influenced weed cover at the Late termination time only. Neither plant N concentration in the cover crop mulch nor soil nitrate influenced weed cover. The results of this study indicate that cover crop biomass and termination timing are important factors influencing weed cover and termination effectiveness in cover crop mulch.
Integrating cover crops (CC) in rotations provides multiple ecological services, but it must be ensured that management does not increase pre-emptive competition with the subsequent crop. This experiment was conducted to study the effect of kill date on: (i) CC growth and N content; (ii) the chemical composition of residues; (iii) soil inorganic N and potentially mineralizable N; and (iv) soil water content. Treatments were fallow and a CC mixture of barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) sown in October and killed on two different dates in spring. Above-ground biomass and chemical composition of CC were determined at harvest, and ground cover was monitored based on digital image analysis. Soil mineral N was determined before sowing and after killing the CC, and potentially mineralizable N was measured by aerobic incubation at the end of the experiment. Soil water content was monitored daily to a depth of 1.1 m using capacitance sensors. Under the present conditions of high N availability, delaying kill date increased barley above-ground biomass and N uptake from deep soil layers; little differences were observed in vetch. Postponing kill date increased the C/N ratio and the fiber content of plant residues. Ground cover reached >80% by the first kill date (∼1250°C days). Kill date was a means to control soil inorganic N by balancing the N retained in the residue and soil, and showed promise for mitigating N losses. The early kill date decreased the risk of water and N pre-emptive competition by reducing soil depletion, preserving rain harvested between kill dates and allowing more time for N release in spring. The soil potentially mineralizable N was enhanced by the CC and kill date delay. Therefore kill date is a crucial management variable for maximizing the CC benefits in agricultural systems.
The introduction of cover crops in the intercrop period may provide a broad range of ecosystem services derived from the multiple functions they can perform such as erosion control, recycling of nutrients or forage source. However, the achievement of these services in a particular agrosystem is not always required at the same time or to the same degree. Thus, species selection and definition of targeted objectives is capital when growing cover crops. The goal of this work was to describe the traits that determine the suitability of five species (barley, rye, triticale, mustard and vetch) for cover cropping. A field trial was established during two seasons (October-April) in Madrid (central Spain). Ground cover (GC) was monitored with 21 and 22 samples, and biomass measured 8 and 10 times, respectively for each season. A Gompertz model characterized GC until the decay observed after frosts, while biomass was fitted to Gompertz, logistic and linear-exponential equations. At the end of the experiment carbon (C), nitrogen (N), and fibre (neutral detergent, acid and lignin) contents, and the N fixed by the legume were determined. The grasses reached the highest GC (83-99%) and biomass (1226-1928 g/m2) at the end of the experiment. With the highest C/N ratio (27-39) and dietary fibre (527-600 mg/g) and the lowest residue quality (~680 mg/g), grasses were suitable for erosion control, catch crop and fodder. The vetch presented the lowest N uptake (2.4 and 0.7 g N/m2) due to N fixation (9.8 and 1.6 g N/m2) and low biomass accumulation. The mustard presented high N uptake in the warm year and could act as a catch crop, but low fodder capability in both years. The thermal time until reaching 30% GC was a good indicator of early coverage species. Variable quantification allowed finding variability among the species and provided information for further decisions involving cover crops selection and management.
Weeds are a major constraint for organic crop production. Previous research has found that cover crops in reduced tillage systems can provide weed interference, subsequently reducing inputs and improving crop yield. However, questions remain about effects of cover crop species identity and cover crop biomass on weed suppression and crop yield. This four-year study investigated how winter cover crops grown alone or in mixture influenced weed presence and crop yield in a reduced tillage organic vegetable system. Treatments were barley (Hordeum vulgare L.), crimson clover (Trifolium incarnatum L.), mixed barley + crimson clover, and a no-cover crop control. Plots were flail-mowed and strip-tilled prior to planting main crops (2011 and 2012: broccoli Brassica oleracea L.; 2013 and 2014: crookneck squash Cucurbita pepo L.). We measured density, diversity, and community composition of weeds and viable weed seeds, changes in weed percent cover within growing seasons, and crop yield. We found that the presence of barley, crimson clover, or barley + crimson clover reduced weed density by 50% relative to the control. Cover crop biomass negatively influenced weed density and weed seed diversity, and positively influenced squash yield. Weed percent cover within growing seasons did not respond differentially to cover crop treatment. Cover crop treatment and cover crop biomass had no influence on weed or weed seed community composition. These results suggest that reduced tillage winter cover crops in mixture or monoculture can similarly suppress weeds and improve yield, primarily due to biomass effects.
The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) benefits the health, nutrition and abiotic stress tolerance of the host plant. The maintenance of potential AMF inoculum in the winter is important because it will affect the colonization process in the subsequent crop. The objective of this study was to evaluate the effect of winter cover crops (CC) on AMF parameters (root colonization, length of hyphae and number of AMF spores), other variables indirectly related to AMF (the easily extractable glomalin-related soil protein (EE-GRSP) and the enzymatic activity of β-glucosaminidase), along with water-stable aggregates (WSA) as a soil quality indicator. In addition, the effect of two sampling dates on the variables in maize and the relationships among all of the variables were studied. The samples were obtained from a field experiment established in 2006 located in Aranjuez (Central Spain) under a Mediterranean semiarid climate. The treatments were winter cover crops of barley (Hordeum vulgare L.) or vetch (Vicia villosa L.) and fallow as a control. The study covered two seasons in 2011–12 and 2012–13 with sunflower (Helianthus annuus L.) and maize (Zea mays L.) as the main crop, respectively, with both sown in the spring. The main crops were irrigated according to the crop demand. Compared with the bare fallow conditions, cover crops improved most of the variables, maintaining the benefits of CC on AMF under the semiarid conditions of the Mediterranean climate. Barley as a cover crop gave the best results, whereas the performance of vetch was poorer. In sunflower, barley increased by 80% the hyphae length and β-glucosaminidase activity and by 30% other variables compared with the fallow; whereas in maize, 60–70% increments were found in AMF spores and the hyphae length and 2-fold in the enzyme activity. The sampling date affected all of the variables analyzed in the maize crop, except for the EE-GRSP and the WSA. Positive relationships were found between the variables directly related to AMF, EE-GRSP content and β-glucosaminidase activity. This suggests that the variables indirectly related to AMF, mainly the EE-GRSP, could be used as indicators of AMF. Finally, the enhancement of soil aggregate stability by the CC via AMF promotion was corroborated.
Soil dispersion in an aqueous solution of sodium hexametaphosphate and sodium bicarbonate facilitates extraction of seeds by flotation with megnesium sulphate. The percentage viability of seeds collected in this manner subsequently can be determined with 2,3,5-triphenyl-tetrazolium chloride. Extraction of seeds usually is 100% efficient and enumeration of viable seeds via the tetrazolium test is accomplished much more rapidly than with conventional methods.