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Is there a critical level of organic matter in the agricultural soils of temperate regions: A review
Abstract
Soil organic matter (SOM) is a complex mixture, which influences a number of soil properties and nutrient cycling, and is itself influenced in kind and amount by land-use, soil type, climate and vegetation. There is considerable concern that, if SOM concentrations in soils are allowed to decrease too much, then the productive capacity of agriculture will be compromised by deterioration in soil physical properties and by impairment of soil nutrient cycling mechanisms. This has clear implications for the sustainable use of soil. We have focussed our discussion from the standpoint of the sustainability of UK agriculture, because we know that best, but similar concerns are equally valid elsewhere in the world. Although soil scientists would expect to find different behaviour in different soils at different ‘critical’ concentrations of SOM, it seems widely believed that a major threshold is 2% soil organic carbon (SOC) (ca. 3.4% SOM), below which potentially serious decline in soil quality will occur.
... One of the keystones of sustainable farming is appropriate care for the soil organic matter. Soil organic matter (SOM) content and quality influence a wide range of physical, chemical and biological attributes, and processes, including the formation and stabilisation of soil aggregates, nutrient cycling, water retention, disease suppression, pH buffering and cation exchange capacity (3,4). Additionally, soil carbon sequestration can be part of the solution in tempering the adverse impact of climate change. ...
... 2) Average yearly dose depends on the nutrient content in sewage sludge. 3) Average yearly dose depends on the nutrient content in farmyard manure. 4) Average yearly dose depends on the nutrient content in straw. ...
The soil organic matter (SOM) content and quality are the fundamentals of soil fertility and contribute significantly to soil carbon sequestration. The soil glomalin content is increasingly recognized as an indicator of SOM quality. The objective of this study was to evaluate the capability and contribution of the easily extractable glomalin (EEG), total glomalin (TG) content, potential wettability index (PWI) of soil aggregates, and water stability of soil aggregates (WSA) as instrumental indicators of long-term SOM quality changes. The obtained results on EEG, TG, PWI, and WSA were compared to the results of humic substances fractionation, specifically their relationship to carbon in humic substances, humic acids, and fulvic acids (C HS , C HA , and C FA , respectively). We used long-term field experiments (27 years) with a simple crop rotation starting with potatoes (site A) or maize (site B), followed by winter wheat and spring barley (on both sites) on the luvisol soil type. Fertiliser treatments were based on the application of uniform 330 kg N ha ⁻¹ per three years. Treatments were as follows: unfertilised control (Cont), sewage sludge in normal and triple dose (SS1 and SS3, respectively), farmyard manure in the conventional dose and half dose with mineral nitrogen (F1 and F1/2+N1/2, respectively), straw and mineral N fertiliser (N+St), and mineral N only (N). For the evaluation of the fertiliser effect, data from both sites were pooled together. The farmyard manure application in the F1 treatment showed the best potential for improving the SOM quality (the highest C HA , humification rate, humification index, TG content, and WSA). The results of Cont treatment show degradation of SOM content and quality. No significant effect of fertiliser treatment on the EEG was observed. The TG content was significantly influenced by fertiliser in the F1, F1/2+N1/2, and SS3 treatments (1965, 1958, and 1989 mg kg ⁻¹ , respectively) in comparison with the Cont (1443 mg kg ⁻¹ ). The TG content was in a tight relationship with the C HA content (R ² = 0.298; p <0.001). The PWI was also influenced by the treatment. There was a significant positive relationship between PWI and C HS (R ² = 0.550), C HA (R ² = 0.249), and C FA (R ² = 0.492), p <0.001. No significant relationship was established between the WSA and SOM quality indicators. Both TG content and PWI can be used as indicators of SOM quality in long-term experiments. On the other hand, the EEG content and WSA are not capable of determining the changes in the SOM quality.
... A healthy soil is characterized by high or increasing SOM (Loveland, 2003); the benefits of healthy soils for crop production and society have been known for some time (Acton and Gregorich, 1995). Soil health is commonly defined as the ongoing ability of soil to function as a vital living ecosystem that supports plants, animals, and humans (Lehmann et al., 2020). ...
... SOM is a key soil component that underpins these functions (Lehmann et al., 2020); its management in agricultural soils is a dynamic process that requires a continuous input of fresh organic material (Montgomery, 2007). Understanding the direction and rate of SOM change is critical for addressing soil degradation issues (Loveland, 2003) and should be at the forefront of our efforts to combat climate change (Montanarella and Panagos, 2021). ...
Agriculture can be pivotal in mitigating climate change through soil carbon sequestration. Land conversion to pasture has been identified as the most effective method to achieve this. Yet, it creates a perceived trade-off between increasing soil carbon and maintaining arable food crop production. In this on-farm study, we assessed the potential of incorporating a 2-year diverse ley (consisting of 23 species of legumes, herbs, and grasses) within a 7-year arable crop rotation for soil organic matter accumulation. We established upper and lower boundaries of soil organic matter accumulation by comparing this approach to positive (permanent ley, akin to conversion to permanent pasture) and negative (bare soil) references. Our findings in the 2-year diverse ley treatment show greater soil organic matter accumulation in plots with lower baseline levels, suggesting a potential plateau of carbon sequestration under this management practice. In contrast, the positive reference consistently showed a steady rate of organic matter accumulation regardless of baseline levels. Moreover, we observed a concurrent increase in labile carbon content in the 2-year ley treatment and positive reference, indicating improved soil nutrient cycling and ecological processes that facilitate soil carbon sequestration. Our results demonstrate that incorporating a 2-year diverse ley within arable rotations surpasses the COP21 global target of a 0.4% annual increase in soil organic carbon. These findings, derived from a working farm's practical and economic constraints, provide compelling evidence that productive arable agriculture can contribute to climate change mitigation efforts.
... water holding capacity, infiltration rate and aggregate stability) and chemical (e.g. fertility) properties and biodiversity conservation (Evrendilek et al., 2004;Haynes, 2000;Loveland & Webb, 2003). ...
... Similarly, a meta-analysis found that the response of crop yield to SOC content levels off at around 2% (Oldfield et al., 2019). However, other studies suggest that this threshold depends on environmental conditions, management practices and soil characteristics (Loveland & Webb, 2003). In any case, in this study, we found that 90% of the rainfed agricultural sites had SOC levels below this 2% threshold, whilst 63% of the soils in the corresponding forest reference sites were below this threshold. ...
Native forests host important pools of soil organic carbon (SOC). This is a key element not only for ecosystem functioning, but also for the global carbon cycle. Globally, and particularly in Argentina, native forests are being rapidly replaced by other land uses, raising questions about the impact of these transformations on SOC and its environmental controls. Based on the construction of the largest SOC database in Argentina to date, we investigated the patterns and controls of changes in SOC stocks associated with the replacement of native forests by other land uses. We constructed the database with a total of 818 sites with SOC data (0-30 cm depth), covering the main ecoregions, to which we added environmental information (e.g. satellite data, soil database, climate database), in order to study the environmental controls on SOC change after deforestation and on the original SOC content of native forests. Considering all ecoregions and all land use alternatives together, we found an average decrease in SOC stock of 18.2 Mg C ha-1, which represents a loss of more than a quarter of the original SOC stock of the native forest sites. A boosted regression tree explained 89% of the variation in SOC stock change and indicated that the initial forest SOC stock and the post-deforestation land use were the most important variables explaining this variation (relative influence of 30.9% and 18.2%, respectively). The replacement of native forests by rainfed annual crops resulted in the largest decrease in SOC (-28 Mg C ha-1), which was twice as large as the decrease observed in rangelands (-14 Mg C ha-1). On the contrary, neither irrigated croplands nor tree plantations of fast-growing species caused a decrease in SOC stocks (p>0.10). Climate and soil texture had an indirect effect on SOC changes through a strong influence on the initial SOC stocks in native forests (p < 0.01). Our study highlighted the significant impact of land use change on SOC stocks, overshadowing other relevant environmental controls. Understanding how the SOC pool responds to land use change, environmental conditions, and management practices is essential to increase the effectiveness of practices implemented to improve soil properties and mitigate climate change.
... The mean organic matter content in the top depth was 3.6% and decreased to less than 3% in the subsequent layer, resulting in up to 30% decrease in the 5-to 15-cm layer compared to the 0-to 5-cm depth. It was only the top 0-5 cm that had a mean SOC greater than the minimum critical range, which is~2% (Loveland & Webb, 2003), suggesting the overall soil organic matter in the study site was considerably low. ...
... Generally, it was low, irrespective of treatments, depth, or year. It was mostly below 2%, known as the "critical level" (Loveland & Webb, 2003), below which soils may lack the capacity to support proper ecosystem functions. ...
Continuous land disturbance could negatively impact microbial community, but perennial crops can potentially reverse this negativity. The objective of this study was to evaluate the effects of Kernza (Thinopyrum intermedium) and alfalfa (Medicago sativa L.) on soil microbial structure and stress condition using the phospholipid fatty acid profiling. The study was conducted at the Ross Jones Research Farm, University of Missouri and consisted of four treatments: Kernza fertilized, Kernza unfertilized, Kernza and alfalfa intercrop, and alfalfa monocrop with four replications. Treatments were established in September 2021 on 18.3 m × 18.3 m plots. Soils from 0‐ to 5‐cm and 5‐ to 15‐cm depths were sampled in September 2021 (before treatments were placed) and 2022 and analyzed for microbial communities. All microbial communities increased after 1 year with the perennial crops. Since differences were not significant among treatments in 2022, this may lead to positive impacts of perennial crops on microbial communities, irrespective of the crop species and management. Moreover, community structure modifications were also observed with the perennial crops, irrespective of the species and management, as evidenced with changes in bacterial community indices in 2022. While fungi/bacteria ratio increased, Gram‐positive/Gram‐negative bacteria ratio decreased in 2022, suggesting a reduction in microbial stress, which can be attributed to ecological functions of the perennial crops. The study showed improvements in soil microbial biomass and modifications in microbial community structure after 1 year of Kernza and alfalfa. As the system matures, relative benefits of management (fertilization and intercropping) and plant species may be realized.
... These materials directly or indirectly participated in the formation of soil aggregates, promoted the accumulation of organic carbon, and affected SOC stock [15,16]. However, their effectiveness in some soils has been questioned, such as those soils with low clay content and low water content [17][18][19]. One alternative to mitigate these problems could be applying amendments consisting of organic matter (i.e., straw) combined with clay minerals (i.e., illite, kaolinite, montmorillonite, etc.). ...
... In addition, our results indicated that soil bulk density showed a negative correlation with >0.25 mm aggregates and their associated organic carbon concentration and SOC stock. Coarse structure is one of the most important factors limiting SOC stabilization in sandy soils [19]. This was consistent with previous research, which found that fine-textured soils had high SOC [47]. ...
Soil amendments have been proposed as an effective way to enhance soil carbon stocks on degraded soils, particularly in dryland farming areas. Soil organic carbon (SOC) plays an important role in improving soil quality, and soil aggregates are known to be crucial in sequestering and protecting SOC. However, how aggregation and protection of SOC by aggregates respond to a single application of bentonite combined with maize straw remains unknown, especially in the sandy soil of a semi-arid region. A three-year field experiment with four treatments [no amendment (CK), maize straw amendment addition only (T1, 6 Mg ha⁻¹), bentonite amendment addition only (T2, 18 Mg ha⁻¹), and maize straw combined with bentonite amendment (T3, 6 Mg ha⁻¹ maize straw plus 18 Mg ha⁻¹ bentonite)] was conducted in the Loess Plateau of China to assess the effects of bentonite and maize straw on aggregation and SOC. The results indicated that soil bulk density decreased by 2.72–5.42%, and soil porosity increased by 3.38–8.77% with three years of T3 application, especially in the 20–40 cm layer, compared with CK. T3 increased the amount of C input, SOC stock, and SOC stock sequestration rate by 1.04 Mg ha⁻¹ y⁻¹, 0.84–1.08 Mg ha⁻¹, and 0.49 Mg ha⁻¹ y⁻¹, respectively, and it increased the mass proportions and aggregate-associated C stock of >0.25 mm aggregates by 1.15–2.51- and 1.59–2.96-fold compared with CK. Correlation analysis showed a positive correlation of total SOC stock with the C concentration of >2 mm, 0.25–2 mm, and 0.053–0.25 mm aggregates. Aggregates of various sizes in sandy soils have the potential for greater SOC stock. Our findings suggest that the application of maize straw (6 Mg ha⁻¹) combined with bentonite (18 Mg ha⁻¹) would be an effective management strategy to enhance the bulk soil C pools by improving the soil structure and thereby improving soil fertility.
... threshold for productive cropping in temperate regions(Loveland and Webb, 2003), with levels below ...
Pongamia pinnata (Linn.) Pierre, also called Millittia pinnata or Indian beach, is a fast-growing legume tree that has gained considerable attention for its potential as a feedstock for biofuel. In this study, we assessed the growth characteristics and carbon sequestering potential of Pongamia grown under sub-tropical environments. At two different sites located in Queensland, Australia, Pongamia was found to produce considerable biomass, even when planted in nutrient-poor environments having low soil organic carbon. The seedlings planted were all derived directly from genetically diverse, yet related seed. Variability observed in growth appeared to be associated with the mother tree from which the seeds were sourced, underscoring the importance of planting elite genetic material for commercial purposes. Pongamia is known to be drought tolerant, with findings here demonstrating that even young seedlings have this characteristic. Collectively, our findings indicate that Pongamia can grow quickly, reaching a biomass of 13-19 kg over 3-4 years in our studies, and sequester high quantities of carbon, at 2.9 to 4.0 t of carbon per ha (assuming a tree density of ~450/ha), even when planted in suboptimal growing conditions on marginal, nutrient-poor lands.
... Generally, in clay soils, OM below 2% indicates a significantly depleted situation. The high OM of 3.8% at some locations might be attributed to manure application and the addition of carbon through burning crop residues, a common winter practice in agricultural areas (Loveland & Webb, 2003). N (%) varied from 0.01 to 0.42%, with a mean value of 0.11% in the soil samples, signifying low N (%). ...
The continuous release of heavy metals (HMs) from nearby industries leads to the contamination of surrounding agricultural areas. This study employed an integrated approach, combining contamination factor (CF), enrichment factor (EF) and geo-accumulation index (Igeo) for pollution assessment, alongside source apportionment using principal component analysis (PCA) and Geographic Information System (GIS)-based positive matrix factorization (PMF), to evaluate HM contamination in agricultural soils of the northeast Guntur district, India. The mean concentrations of HMs, Cu, Cr, Zn, Ni, Cd and Pb exceeded the Indian natural background soil values by 2.59, 1.21, 2.24, 2.09, 1.15 and 1.4 respectively. Pollution indices revealed high contamination for Ni (CF = 2.21) and Cr (CF = 2.05), with Cr showing moderate enrichment (EF ≈ 1.5) and contamination (Igeo = 0.75). PCA identified three components explaining 78.37% of the total variation while GIS-based PMF identified industrial discharges, waste incineration, agriculture and vehicular and industrial emissions as pollution sources. Ni, Cu and Cr were identified as the primary contaminants, with industrial emissions, vehicular traffic and agricultural activities as key contributors to HM pollution. Cr accounted for ~ 80% of the total hazard index, posing significant non-carcinogenic risks for children via ingestion. Carcinogenic risks through ingestion of Ni and Cr were 2.8 and 1.9 times higher than acceptable levels for adults and 3.9 and 2.6 times higher than acceptable levels for children. Additionally, the high bioconcentration factor (BCF) of Lantana viburnoides (Forssk.) with a BCF of 18.29 for Cd suggests a potential environmental hazard. It is imperative to monitor emissions rigorously to safeguard soil quality and optimize industry standards in this region.
... Owing to a lack of attention for SOM in cultivated soils, agricultural soil has a great potential to sequester carbon. There is a need to conserve and regenerate productive soils by maintaining and building SOM, thereby contributing to sustainable agriculture [119,120]. Soils with critically low SOM (<2%) are widespread on cultivated land. These soils can play a crucial role in carbon (C) sequestration, as they are far from their C saturation point and therefore accumulate and stabilize C quickly [121]. ...
Climate change events significantly impact the food production chain by damaging crops in their most fragile phenological states. Furthermore, increasing human population and excess food waste present agricultural systems with the challenge of closing the yield gap and securing food demands in the future as well as protect the soil health and biodiversity. Biostimulants are a novel alternative in agriculture that can effectively use inputs, enhance crop resilience to abiotic stresses and improve food quality. Additionally, biostimulants offer a promising and eco-friendly solution for reducing the use of chemical fertilizers, as they have the potential to increase crop nutrient use efficiency and yield. Because of their effects on plant growth, a wide range of products can be marketed as biostimulants. Presented in this review is an overview of recent literature on the use of plant growth-promoting microbes and microalgae-derived extracts obtained from either waste streams or recycled substrates. Starting from their source material, extraction technologies and application modalities, a view of their factors shaping the composition and activity of biostimulants is provided to elucidate a mechanistic model of action which leads to increased stress resilience in crops. This work further sets out to understand if the biostimulants can be used to transform waste into a valuable product that can accelerate the transition to sustainable agriculture.
This article is part of the theme issue ‘Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the ‘Resilience Revolution’?’.
... The stronger increase in carbon stocks and contents observed under oregano (compared to thyme) can be explained by the significantly higher primary productivity, i.e., higher above-and belowground biomass production of oregano. In agricultural systems, it is well known that carbon and nitrogen inputs originate from plant shoot and root residues entering the soil ecosystem (Loveland 2003;Castellano et al. 2015;Chenu et al. 2019;Poeplau et al. 2021). Additionally, we observed that aromatic plants may also indirectly impact vineyard soil C and N budgets via acting as a physical barrier, which captures and retains a part of the dropped grapevine leaves in the end of the crop cycle. ...
In vineyards facing soil degradation and biodiversity loss, crop diversification may improve sustainability, but its effects on the soil microbiome remain unclear. In a 3‐year field study, we examined how diversifying the plant row under grapevine with aromatic plants affected topsoil properties (0–10 cm) in an organically farmed, steep‐sloped vineyard. Specifically, we investigated the effects of diversification with oregano and thyme on microbial biomass, respiration, prokaryotic and fungal community compositions, enzyme activities, potential nitrification, and abiotic soil properties, including total and particulate organic carbon (TOC, POC), nutrient status, pH, and soil moisture. Grapevines alone with mechanical tillage served as control. The aromatic plants competed with grapevines by lowering soil nutrient contents and moisture. Aromatic plant litter had a small, mostly non‐significant but consistent effect on POC contents, and POC stocks determined in the final year showed a slight increasing trend in the order control (10.9 ± 2.8 t POC ha⁻¹) < thyme (12.6 ± 3.1) < oregano (13.1 ± 4.1). Surprisingly, these changes coincided with a significant decrease in microbial biomass compared to control, indicating aromatic plant‐microbe competition. Concomitant decreases in respiration and the activity of C‐cycling enzymes but also the metabolic quotient, suggest lower carbon mineralisation but more efficient microbial carbon use. Multivariate statistics revealed that the prokaryotic community was primarily structured by abiotic soil properties, such as organic matter, nutrient and water availability. In contrast, the fungal community exhibited a stronger plant‐specific response, with changes in composition likely driven by root‐associated interactions, suggesting a more direct biotic influence. Especially, arbuscular mycorrhizal fungi and potential nitrification were promoted under both aromatic plants, which may benefit grapevine growth. Overall, we show that diversifying perennial agroecosystems such as vineyards with aromatic plants increases soil habitat heterogeneity with benefits for microbial diversity, carbon sequestration and nutrient cycling, demonstrating its positive impact on soil biodiversity and functioning.
... As a major constituent of SOM, soil organic carbon (SOC) is a critical factor in determining soil quality and productivity. It significantly impacts the soil's physical structure, chemical composition, and biological activity (Loveland and Webb 2003;Yang et al. 2018). While SOM quantity reflects the balance between organic inputs and decomposition rates, it does not necessarily indicate changes in SOM quality . ...
Background and aims
Soil labile organic matter (LOM) plays a vital role in enhancing soil productivity and fertility. However, the annual variability of LOM content and structure under diverse crop rotation and fertilization practices remains insufficiently investigated.
Methods
This 5-year field study investigates the impact of different fertilization treatments—no fertilization (CK), conventional fertilization (CF), recommended fertilization (RF), and recommended fertilization with straw returning (RF + S)—on the content and structure of LOM under oilseed rape-rice (OR) and wheat-rice (WR) cropping systems.
Results
Our results showed that the effect of rotation type on soil LOM was most pronounced during the upland season, while fertilization effects were significant across the entire annual paddy-upland rotation system. During the upland season, the OR rotation, excluding the CF treatment, resulted in significantly higher increases in soil easily oxidizable organic carbon (EOC), particulate organic carbon (POC), and particulate nitrogen (PN) compared to the WR rotation with same fertilization treatments. The RF and RF + S treatments significantly enhanced soil LOM contents in both rotations. Excitation Emission Matrix (EEM) and UV–Visible absorption analyses indicated that the OR rotation had a higher degree of humification, a more aromatic structure, and greater levels of colored dissolved organic matter (DOM) than the WR rotation.
Conclusions
In summary, the OR rotation, especially with straw returning, is an effective strategy for enhancing both the content and structural stability of LOM. This approach promotes improved soil quality and offers a sustainable solution for long-term fertility management in paddy-upland rotations.
Highlights
Rotation and fertilization practices jointly affect soil LOM content and structure.
Oilseed rape in paddy-upland rotation improves LOM content and composition.
The LOM difference between OR and WR rotations mainly appears in the upland season.
... Soil organic carbon is a key indicator of soil health [76,77]. On a global scale, it has been observed that crop productivity and soil functions decline when SOC falls below 2 % [7,8,78,79]. This is likely because of improvements in soil structure and functioning that co-occur with increases in SOC [80]. ...
... Organic matter content is among the most critical soil parameters influencing grass yield, particularly in the conditions studied. Other soil parameters, such as pH, phosphorus and potassium levels, soil texture, and drainage, can also play equally or more significant roles in specific contexts (Celestina et al., 2019;Loveland and Webb, 2003). Although the organic matter content varied between 2.7 % and 5.5 % across different trials (Table 1), it remained consistent within each specific trial. ...
Plasma-based nitrogen (N) enrichment of organic fertilizers is a process that utilizes plasma technology and electricity to infuse liquid biobased fertilizers with atmospheric N, doubling plant-available N content. The final product is labeled as Nitrogen-Enriched Organic Fertilizer (NEO). This study investigates and compares the applicability of NEO against conventional fertilizers in grass production during 2020-2023 across two regions in Norway. Regarding different fertilizers' N efficacy, in the trials featuring only grasses, applying 210 kg N ha − 1 in NEO yielded dry matter (DM) and N yield comparable to those achieved with 149 and 154 kg N ha − 1 in mineral fertilizer, respectively. Besides, the untreated cattle slurry and mineral fertilizer combination containing 210 kg N ha − 1 resulted in a DM and N yield equivalent to 178 and 180 kg N ha − 1 in mineral fertilizer. In the grass-clover mixture trials, NEO and mineral fertilizers reduced the clover proportion, significantly influencing the overall yield. Merging the results from all trials (2021-2022), it was found that given identical N-min content, standalone mineral fertilizer, and the untreated slurry and mineral fertilizer combination resulted in ~19 % and ~28 %, and ~14 % and ~13.5 % higher DM and N yields than NEO, respectively. Further, NEO provided ~9 % and ~25 % higher DM and N yields than untreated slurry. Notably, NEO's N-min content was nearly double that of untreated slurry (210 vs. 107 kg N ha − 1). Nonetheless, a supplementary trial (2023) employing different NEO variants with reduced nitrite and elevated nitrate levels returned more promising results than those examined in prior years. Still, ~9 % and ~6 % less DM and N yield than mineral fertilizer with identical 210 kg N ha − 1 content. Our findings suggest that although a considerable N fraction of NEO did not translate to yields compared to other fertilization treatments, and given that NEO is an evolving product, the NEO's enhanced performance in the final study year highlights the necessity for continued research and optimization to fully unlock and utilize the potential advantages of NEO in future agriculture.
... Even a 1% change in the soil organic matter can easily make observable differences in the physical and chemical properties of the soil. It enhances the water holding capacity of the soil and contributes positively to improving the soil structure by binding the soil particles together (Loveland, 2003). Furthermore, soil organic matter reduces compaction between the granules in clayey soils and reduces the occurrence of the compacted soil layer. ...
Soils are the both source and an important sink for the atmospheric carbon dioxide concentration. Soil organic carbon is also involved in many environmental functions. As a matter of fact, changes in land use and land management practices, changing the soil organic carbon stocks. Prediction of changes in the soil organic carbon stocks both for future and past is an important issue. Thus, modeling is one of the promising methods for the estimation of SOC. RothC carbon turnover model is one of the most using models to predict SOC changes in the arable lands. In this study, I estimated the farm-scale SOC stock changes between the years of 2009-2016 in Nafferton Ecological Farm. Baseline soil organic carbon content established for 2006 as (46.7tC/ha) and the 8 year simulation was run for the four contrasting scenarios;A (minimum tillage + compost application), B (minimum tillage + mineral fertilizer ), C (conventional tillage + compost application), D ( conventional tillage +mineral application). At the end of the simulation period, slight difference observed between the SOC stocks of scenario A and initial condition (0.1tC/ha). For Scenario B and C soil organic carbon stocks obtained lower than the initial condition with the values of (44.8tC/ha ) and 45,8tC/ha. Model prediction and measured values are almost matching except the Scenario D, the differences found at 3.2tC/ha little than the measured value.
... The quality of agricultural soils can be assessed using soil properties as indicators of quality, which allow comparisons among different soils, land uses or agricultural practices (Duval et al., 2013). In agricultural soils, a decrease in soil organic matter (SOM) content is generally associated with loss of aggregate stability (AS) (Abid and Lal, 2008), indicating soil structural degradation and consequently a reduction in soil physical quality (SPQ) (Loveland and Webb, 2003) argued that it's difficult to draw a conclusion on the effect of agricultural practices on AS and changes in SOM because (i) there is not uniform methodology and size range of aggregates for determining AS; (ii) the general assumption of a linear relationship between SOM and AS; meanwhile, nonlinear relationships or non-significant relationships have also been found; (iii) the sampling depth; and (iv) the wide variation in AS within the same soil depending on the type and amount of SOM. Haynes (2000) showed that increasing inputs of organic matter under short-term pasture could result in significant increases in AS without a measurable change in SOM content. ...
... Apart from these sites, large ranges in SOC content (> 2%) were also found at four of the other Swedish sites, and at one Czech (CZE 1), one Lithuanian (LTU 3), and one Swiss (CHE 4) site. The lowest average SOC contents were found in Spain, at a site in Italy (ITA 4), at a Turkish site (TUR 2), and at the Polish site (POL 1), all not exceeding 1%, which has been established as a critical level below which serious decline in soil quality might occur (desertification; Loveland and Webb 2003). Most other sites had average SOC content between 1% and 2%. ...
Multispectral imaging satellites such as Sentinel‐2 are considered a possible tool to assist in the mapping of soil organic carbon (SOC) using images of bare soil. However, the reported results are variable. The measured reflectance of the soil surface is not only related to SOC but also to several other environmental and edaphic factors. Soil texture is one such factor that strongly affects soil reflectance. Depending on the spatial correlation with SOC, the influence of soil texture may improve or hinder the estimation of SOC from spectral data. This study aimed to investigate these influences using local models at 34 sites in different pedo‐climatic zones across 10 European countries. The study sites were individual agricultural fields or a few fields in close proximity. For each site, local models to predict SOC and the clay particle size fraction were developed using the Sentinel‐2 temporal mosaics of bare soil images. Overall, predicting SOC and clay was difficult, and prediction performances with a ratio of performance to deviation (RPD) > 1.5 were observed at 8 and 12 of the 34 sites for SOC and clay, respectively. A general relationship between SOC prediction performance and the correlation of SOC and clay in soil was evident but explained only a small part of the large variability we observed in SOC prediction performance across the sites. Adding information on soil texture as additional predictors improved SOC prediction on average, but the additional benefit varied strongly between the sites. The average relative importance of the different Sentinel‐2 bands in the SOC and clay models indicated that spectral information in the red and far‐red regions of the visible spectrum was more important for SOC prediction than for clay prediction. The opposite was true for the region around 2200 nm, which was more important in the clay models.
... PC4 may project some distinctive or secondary parameters that are not as prejudicial as those normally captured by primary components in determining the bioearth quality, while PC5 These three principal components account for 76.24% of the total variance, highlighting their significance in accounting the primary sources of variability within the dataset. This agrees with typical PCA applications in environmental studies where often initial components capture most of the explained variance by recognizing broad and influential The positive covariances of TOC with N (0.8619) and P aligns with the studies of Loveland and Webb (2003) and Gerke (2022), who found that higher amounts of organic matter usually add to elevated levels of nutrients. The positive correlations for heavy metals, for instance, Zn and Cu, in the matrix reflect the trends reported by Saravanan and Ramesh (2024), where metals frequently co-occur in bioearth due to their similar behaviors and sources. ...
This study presents the chemical properties, nutrient contents, heavy metals and interrelationship amongst various parameters in bioearth, a soil-like material harnessed from legacy waste dumpsites. The analysis indicates an alkaline pH of 7.75, a moderate EC of 1.89 mS cm⁻¹, and a relatively low C content of 4.89%, compared to optimal compost standards. The nutrient levels are suboptimal, with total N, K and P concentrations of 0.45%, 0.37% and 0.23%, respectively, all below the recommended values for effective compost. The C:N ratio of 12.64 suggests a rapid decomposition process, leading to relatively fast nutrient release. Heavy metal analysis indicates that Zn, Cu and Cd are within the safe limits, whereas Ni and Cr show high values, hence posing a potentially high risk. Statistical analysis performed through ANOVA, points out significant (p < 0.05) differences in all variables of the bioearth’s quality parameters at different sites. Pearson correlation analysis reveals complex interrelationships, with strong links between C and N, and significant effects of pH on heavy metal availability. Principal component analyses manifest the predominance of heavy metals followed by nutrients in causing variability among characteristics of the bioearth. Cluster analysis classifies the sites into three distinct clusters on the basis of pH, TOC content and nutrient contents. The results highlight that improving the quality of bioearth requires enhanced waste management practices. Key recommendations include incorporating materials with higher TOC content to boost organic matter and optimizing the bioearth’s nutrient profile. Additionally, it is essential to monitor and control heavy metal levels to ensure bioearth suitability for agricultural and environmental applications. These measures will help optimize the quality of bioearth and its effectiveness in soil enhancement.
... Mean (of 5 years; 2010-2015) maize and wheat yields were also significantly correlated with MWD and labile and recalcitrant C pools within bulk soils and aggregates in both soil layers, implying positive roles of not only soil aggregation and labile C, but also recalcitrant C pools on crop productivity (Ghosh et al., 2018). Even a small increase in SOC can improve soil physicochemical and biological properties and ecosystem services such as nutrient cycling and possible increases in yields (Loveland and Webb, 2003;Bhogal et al., 2009;Blanco-Canqui, 2013). Crop residues act as a continuous source of soil nutrients and SOM (Liu et al., 2014), which improves soil functioning (Bhogal et al., 2009) and thereby yields. ...
... According to the findings, the bulk density, rockiness, sand, SMC, WHC, EC, TN, available-P, Zinc, Nickel and Copper were all shown to be strongly positively linked with vegetation characteristics in LD forest stands. In keeping with our findings, SMC and WHC are often greater in LD forests and vegetation systems with higher organic matter content can greatly enhance the soil characteristics and nutrient cycling (Loveland & Webb, 2003;Joshi & Garkoti, 2023). ...
The land use change pattern from disturbed tropical dry forests has significant impact on vegetation and soil physico-chemical properties, leading to alterations in vegetation structure and diversity. Thus, aim of this study was to better understand how disturbances affect forest vegetation and soil physico-chemical attributes under varied land uses in the deciduous forest region of Vindhyan highlands, India. Soil samples and vegetation analyses were conducted across three distinct disturbed forest sites on three land use types using the quadrate method. The study documented 45 species in the tree layer, with 37 in least disturbed, 33 in moderate disturbed, and 28 in highly disturbed stands. Shannon, Simpson, Evenness, Margalef and β-diversity indices exhibited pronounced variations among the three disturbed stands. A two-way analysis of variance (ANOVA) revealed significant difference in soil physico-chemical properties (p < 0.001, p < 0.01 and p < 0.05) due to various disturbed forest stands and land use types. Micronutrients such as zinc, copper, and nickel showed significant variation, with higher concentrations in least disturbed stands. Pearson’s correlation analysis indicated strong relationships between vegetation characteristics and soil physico-chemical attributes, consistent across disturbances. Additionally, the principal component analysis indicated that the first four principal components accounted for 77.7% of the total variation in the data. The comprehensive research will add forest managers in developing long-term eco-restoration plans that will result in reduced soil loss and degradation. This study contributes to more effective forest management and conservation efforts by providing essential insights into the interactions between disturbances, vegetation, and soil properties.
... In terms of climate change mitigation, the highest possible SOC content is aimed, which, however, would likely be associated with increased nitrogen losses through increased nitrous oxide emissions and/or nitrate outputs (Guenet et al., 2021;Körschens and Schulz, 1999;Lugato et al., 2018). It should also be noted, that in many cases a particular soil function is more closely related to individual SOM fractions (particulate organic matter (POM), MAOM) than to the absolute SOM content (Loveland, 2003;Wessolek et al., 2008). Körschens and Schulz (1999) used data from long-term observations at Bad Lauchstädt in central Germany to derive target SOC values as a function of clay content in order to preserve the buffer and the production function of soils. ...
Soil organic carbon (SOC) is a key property for soil productivity and functionality. According to the Federal Soil
Protection Act in Germany, site-specific SOC contents need to be maintained in the course of agricultural land use
in order to ensure soil fertility and the performance of soils as a natural resource. In this study, representative
SOC benchmarks have been derived for arable mineral soils in Bavaria on the basis of a comprehensive soil organic
matter (SOM) monitoring program as reference values for farmers and other stakeholders. Data from 283
representative study sites across Bavaria has been stratified according to the most influential site factors on SOC,
particularly clay content and the elevation above sea level as a proxy for climate (temperature and precipitation).
Due to an evaluation of the study sites in terms of agricultural management according to the principles of good
agricultural practice combined with statistical exclusion of 25 % of extreme SOC contents, the benchmarks presented
here can be regarded as representative reference values under specific environmental conditions. However,
different management measures within the principles of good agricultural practice also influenced SOC, as
organic fertilization and the cultivation of perennial forage crops positively affected SOC contents. In contrast,
the cultivation of root crops negatively influenced SOC contents, while the proportion of corn within the crop rotation
of up to 50 % did not affect SOC negatively. We further evaluated the suitability of the SOC/clay ratio as
alternative SOC and soil structure indicator. However, the SOC/clay ratio seems to be inappropriate due to a high
number of degraded sites and a systematic bias towards degradation with high clay contents. The SOC benchmarks
presented here provide valuable reference values for farmers policymakers and agricultural stakeholders
in optimizing cropland management practices for sustainable soil health and fertility in Bavaria and beyond.
However, further research is required regarding the stratification approach and the calculation method for a
widespread implementation of SOC benchmarks. Furthermore, the shifting baseline syndrome has to accounted
for, so up to date SOC benchmarks remain within a range in which soils are considered healthy and fertile.
... It contributes significantly in reducing the effects of climate change and increases land productivity by enhancing soil characteristics like moisture retention and nutrient availability (Van Keulen, 2001;Purakaystha et al., 2019;Singh et al., 2022). The amount of clay in the soil has a crucial role in the buildup of SOC (Christensen, 1992;Loveland et al., 2003). In temperate regions, the conversion of natural ecosystems to agro ecosystems depletes 60% of the stock of SOC, while in tropical regions; the figure is 75% (Lal, 2004). ...
... Soil organic matter (SOM) has a significant impact on soil functioning, and SOM characterization is included in the evaluation of soil health (Gregorich et al., 1994;Reeves, 1997;Loveland and Webb, 2003;Weil and Magdoff, 2004;Lal, 2009;Garrigues et al., 2012;Cotrufo and Lavallee, 2022;Weng et al., 2022). The chemical composition and content of SOM could be affected by the type of irrigation water. ...
Treated wastewater (TWW) irrigation may harm soil and agricultural production. Adverse effects of TWW irrigation may be mitigated by changing irrigation water quality (e.g., fresh water, FW), or management (e.g., a lower frequency irrigation [LFI] with TWW). The influence of mitigation treatments on soil and water-extractable organic matter (SOM and WEOM, respectively) is unknown. To examine this influence, a study was conducted in an avocado orchard irrigated from 2009 with secondary TWW. Four parallel treatments were applied for six years (2016-2021), involving irrigation with (1) FW, (2) a 1:1 FW-TWW mix, (3) TWW at LFI, and (4) TWW irrigation as control. Soil samples from three depths were characterized for organic and inorganic carbon, nitrogen, and by mid-infrared spectra decomposed into components using nonnegative matrix factorization. Aqueous extracts of the samples were characterized for dissolved organic carbon (DOC), inorganic carbon and nitrogen concentrations, absorbance at 254 nm (Abs254), and excitation-emission matrices of fluorescence decomposed into components using parallel factor analysis. Abs254 and fluorescence of humic-like components in the soil extracts were the attributes most consistently responding to irrigation water quality. Irrigation with FW and 1:1 FW-TWW mix led to decreases in concentrations of aromatic and humic-like constituents in the soil extracts compared with TWW irrigation. Changing soil irrigation management had no or little impact on those attributes compared with the control TWW irrigation. Results of the study support the use of optical properties related to the concentrations of UV-absorbing and light-emitting constituents in soil extracts, rather than the whole DOC concentration, as sensitive descriptors suitable for evaluating soil response in different agricultural scenarios.
... One of the primary indicators of soil quality is the content of organic matter in its composition, especially humus, which plays a significant role in shaping its properties: physically (density, aggregate stability, water retention), physicochemically and chemically (ion exchange, buffering capacity, solubility and migration of elements, environmental detoxification), as well as biologically (providing nutrients and energy for microorganisms, biostimulation of plant growth and development, regulation of biodiversity) [1][2][3][4]. The most important components of soil organic matter are humic substances, which are formed as a result of the humification of organic residues. ...
The production of fruit tree seedlings generates waste wood biomass, which results from the pruning of budded rootstocks in the first year of the two-year production cycle. This study proposes a new method of managing this biomass by recycling the wood chips (2, 3 and 5 t ha⁻¹) back into the soil. The impact of different wood chip doses on selected physicochemical soil properties after the production process (especially soil organic carbon content (SOC), as well as the quantity and quality of the produced Malus domestica fruit tree seedlings, was determined. The recycling of waste biomass contributed to enriching the soil with additional components, mainly organic carbon with the potential for biotransformation into humic substances. The applied doses of wood chips, in amounts of 2, 3, and 5 t ha⁻¹, resulted in an increase in SOC content compared to the control by 21.5%, 22.5%, and 35.8%, respectively. Additionally, the recycling of waste biomass introduced other compounds important for plant growth and development into the soil, particularly iron, zinc, magnesium, and manganese. It should be noted that the proposed method of managing waste biomass generated during the apple tree seedling production stage resulted in reduced production costs while maintaining high production indices.
... The findings demonstrated a favorable correlation between the maize yield and 0-10 cm soil quality ( Figure 8b). Improved soil quality increases yield stability and the ability of crops to cope with adversity while maintaining yield (Loveland & Webb, 2003). However, yields vary from region to region due to climatic conditions and soil texture (Lin et al., 2023). ...
Despite conservation tillage being a promising strategy to mitigate soil degradation, the intricate role of microbial communities in shaping soil quality over long‐term tillage remains poorly understood. The study aimed to investigate the microbial mechanisms governing the soil quality index (SQI) and maize yield under different tillage practices spanning 13 years, including no‐till without straw retention (NT0), no‐till with straw retention (NTSR), plough tillage with straw retention (PTSR), and rotary tillage with straw retention (RTSR). The findings revealed that NTSR improved the SQI index by 22.4% and 11.3% higher than PTSR and RTSR, respectively, within the 0–10 cm soil layer. This improvement was correlated with an increase in maize yield (R² = 0.39, p < 0.05). PERMANOVA analysis confirmed that both soil depth and tillage practices significantly impacted the composition of microbial communities (p < 0.05). Furthermore, conservation tillage, compared to PTSR and RTSR, increased the abundance of arbuscular mycorrhizal symbiosis by 78.6%–460.3% but decreased the saprophytic fungal abundance by 27.5%–28.3%. Soil quality was notably influenced by the interaction between bacterial and fungal communities. The presence of bacterial‐dominated Module 2 was associated with decreased soil quality in the 0–10 cm soil depth (r = −0.47, p < 0.01). This study emphasizes the pivotal role of microbial diversity and dominant taxa in driving soil quality after long‐term conservation tillage practices. Understanding these mechanisms is crucial for establishing farmland management to achieve agricultural and ecological sustainability in the face of climate change and soil degradation challenges.
... 2023). Regarding specifically the biological indicators, we completed the Biofunctool set with measures of SOC content and stability given their essential impact on to soil biotic and abiotic properties like water and nutrient retention, resistance against compaction and erosion (Loveland and Webb, 2003;King et al., 2020). Finally, while Biofunctool indicators already include measures of microbial and mesofauna activity, we added at the macrofauna scale an abundance measure of earthworms that are considered the primary ecosystem engineers in temperature climates (Syers and Springett, 1984;Tomati and Galli, 1995;Kooch and Jalilvand, 2008;Le Bayon et al., 2017). ...
Terrestrial enhanced rock weathering (ERW) is a promising carbon dioxide removal technology that consists in applying ground silicate rock such as basalt on agricultural soils. On top of carbon sequestration, ERW has the potential to raise the soil pH and release nutrients, thereby improving soil fertility. Despite these possible co-benefits, concerns such as heavy metal pollution or soil structure damage have also been raised. To our knowledge, these contrasted potential effects of ERW on soil fertility have not yet been simultaneously investigated. This field trial aimed at assessing the impact of ERW on biological, physical, and chemical soil properties in a temperate agricultural context. To do so, three vineyard fields in Switzerland were selected for their distinct geochemical properties and were amended with basaltic rock powder at a dose of 20 tons per hectare (2 kg.m−2). On each field, basaltic rock powder was either applied one year before the sampling campaign, one month before the sampling campaign, or not applied (control) for a total of 27 plots with 9 repetitions of each level. Overall, basaltic rock powder addition had a predominantly positive to neutral effect on soil fertility. Most soil properties showed no significant change either 1 month or 1 year post application. Nevertheless, our study highlighted a significant increase in earthworm abundance (+71 % on average), soil respiration (+50 %) and extractable sodium concentration (+23 %) as early as 1 month post application. The higher soil respiration raises the question of CO2 losses from organic matter mineralization that could limit ERW's efficiency. The increase in sodium raises concerns about a sodification risk potentially damaging soil fertility. These elements now require further investigation before enhanced rock weathering can be considered a viable and secure carbon dioxide removal technology.
... The soils were poor in TN (ranging from 0.1 to 0.9 g kg À1 ), levels similar to those previously observed by An et al. (2018). They were also low in TOC (< 4.9 g kg À1 ), which is lower than the optimal threshold for vegetation growth (20 g kg À1 ) (Loveland & Webb, 2003). and low organic matter concentration, whereas organic-rich soil typically exhibits high TN and TOC:TN (Matschullat et al., 2018). ...
Desiccation of the Aral Sea has resulted in the emergence of vast saline and flat terrains, jeopardizing human health and agricultural activities because of sand and dust storms. Vegetation, mainly indigenous Haloxylon species, has been introduced to ameliorate the soil. As a critical indicator of rehabilitation, the physicochemical properties of soil after the introduction of vegetation remain poorly understood. This study examined (1) the changes in topsoil properties after vegetation establishment based on a 30‐year chronosequence and employed (2) site comparisons of topsoil properties between two cases of natural versus introduced vegetation on a dried Aral Sea bed. Twelve paired areas that were naturally or artificially vegetated during 1990, 2000, 2005, 2008, 2013, and 2017 were selected for examination. Irrespective of vegetation type, increases in organic matter and nutrients (TOC >90%, TN >143%, and P2O5 >23%) were detected in the surface soil (0–10 cm) along the 30‐year chronosequence. In addition, decreases in ECe (92% and 69%), CEC (41% and 11%), Ca²⁺ (38% and 12%), and TIC (81% and 11%) were observed in both natural and introduced vegetation, respectively. The introduced vegetation was associated with a slightly greater accumulation of soil K⁺ and TN than the natural vegetation. Our results indicate vegetation‐derived nutrient and organic matter accumulation as well as the possible removal of salts by root exudates in the surface soil. Overall, vegetation contributed to soil amelioration, with similar effects observed at naturally and artificially vegetated sites.
... Previous global and regional studies on maize (Zea mays) (Oldfield et al., 2019), wheat (Oldfield et al., 2020), and corn and soybean [Glycine max (L.) Merr.] (Kravchenko & Bullock, 2000) have shown that small differences in SOM at low levels (≤4%) have a greater impact on crop productivity compared to large differences at high levels (>4%). However, there is a lack of quantitative evidence on the effect of SOM on crop yields on sandy soils worldwide (Loveland & Webb, 2003). Although many studies now make reference to the positive effects of SOM on crop yields (Ghaley et al., 2018;Lal, 2020;Schjønning et al., 2018), there is almost no quantitative information on the effect of the increase in SOM on potato productivity on sandy soil. ...
While many studies note the positive effects of soil organic matter (SOM) on crop yields, there is limited quantitative information on the influence of increased SOM on potato (Solanum tuberosum L.) productivity in sandy soil. This study estimated the impact of varying SOM on potato productivity in sandy soils and explored whether nitrogen (N) mineralization served as a primary mediator. Soil from nine fields in Wisconsin (SOM range of 1.1%–3.8%) was collected for a greenhouse study. Both NH4‐N and NO3‐N extracted from ion strips and potentially mineralizable nitrogen (PMN) were used as the proxies for N mineralization. Linear mixed effect models indicated that fresh matter whole biomass and dry matter vine biomass were 0.45 and 0.54 times greater at 3.8% SOM compared to 1.1% SOM at an optimal soil pH of 5.2, respectively. Similarly, total N uptake in the whole and vine biomass was 0.51 and 1.0 times higher at 3.8% SOM than 1.1% SOM, respectively. While PMN demonstrated a positive correlation with SOM, it only partially mediated the effect of SOM on productivity, specifically in N uptake in the vines. However, for most productivity measures, including PMN with SOM in the models did not substantially reduce the estimated SOM effect on productivity, indicating that SOM affected productivity mostly through mechanisms other than N acquisition by plants available through mineralization of OM. The study underscored the complex interplay between SOM and potato productivity, urging further research into the multifaceted roles of SOM in sandy soils.
... The soil samples collected within the river Po basin were split into four soil aggregate stability classes according their SOM content. The SOM thresholds were defined combining the classification of Greenland et al. (1975), also reported in Loveland and Webb (2003), with the organic content classes indicated by EIP-AGRI Focus Group Soil Organic Matter in Mediterranean regions (2015). The resulting classes are: (i) very unstable with SOM < 1.72 %; (ii) unstable from 1.72 % to 3.4 % of OM; (iii) stable from 3.5 % to 4.3 %; (iv) very stable with OM >4.3 %. ...
... Nowadays, even if soil is one of the largest pools in the global carbon cycle and it plays a multifaceted role in enhancing the productivity of agricultural soils (e.g. Ref. [9]), there are still large uncertainties regarding the determination of its flux dynamics (e.g. Refs. ...
The quantification of soil carbon dioxide (CO2) flux represents an indicator of the agro-ecosystems sustainability. However, the monitoring of these fluxes is quite challenging due to their high spatially-temporally variability and dependence on environmental variables and soil management practices.
In this study, soil CO2 fluxes were measured using a low-cost accumulation chamber, that was realized ad hoc for the surveys, in an orange orchard managed under different soil management (SM, bare versus mulched soils) and water regime (WR, full irrigation versus regulated deficit irrigation) strategies. In particular, the soil CO2 flux measurements were acquired in discontinuous and continuous modes, together with ancillary agrometeorological and soil-related information, and then compared to the agrosystem scale CO2 fluxes measured by the eddy covariance (EC) technique.
Overall significant differences were obtained for the soil CO2 discontinuous fluxes as function of the WR (0.16 ± 0.01 and 0.14 ± 0.01 mg m⁻² s⁻¹ under full irrigation and regulated deficit irrigation, respectively). For the continuous soil CO2 measurements, the response observed for the SM factor varied from year to year, indicating for the overall reference period 2022-23 higher soil CO2 flux under the mulched soils (0.24 ± 0.01 mg m⁻² s⁻¹) than under bare soil conditions (0.15 ± 0.00 mg m⁻² s⁻¹). Inter-annual variations were also observed as function of the day-of-year (DOY), the SM and their interactions, resulting in higher soil CO2 flux under the mulched soils (0.24 ± 0.02 mg m⁻² s⁻¹) than under bare soil (0.15 ± 0.01 mg m⁻² s⁻¹) in certain periods of the years, according to the environmental conditions.
Results
suggest the importance of integrating soil CO2 flux measurements with ancillary variables that explain the variability of the agrosystem and the need to conduct the measurements using different operational modalities, also providing for night-time monitoring of CO2. In addition, the study underlines that the small-scale chamber measurements can be used to estimate soil CO2 fluxes at orchard scale if fluxes are properly scaled.
The way plant roots facilitate water infiltration in soil may be just as important as the efficiency with which the root system in turn extracts it from the soil. Here we studied the mechanisms through which the root system facilitates water infiltration through a dry soil layer. Dye tracing experiments were conducted in model soil microcosms to characterise how root growth and exudation affects the permeability of dry layers of the model soil. Results showed that dissolved root exudates may be the primary facilitator of water infiltration, which may be linked to water surface tension. We conclude that in dry soil, root architecture and root exudation may combine to facilitate the infiltration of water and decrease the water lost by evaporation. These findings could enhance our understanding of the traits that provide drought resistance in crops.
Oglekļa uzkrājums 0-40 cm dziļumā, atsijājot ekstrēmās oglekļa uzkrājuma vērtības, aramzemēs ir 83,0 tonnas ha-1, ilggadīgajos zālājos – 88,6 tonnas ha-1, bet LIZ vidēji – 85,6 tonnas ha -1. Pētījumā nav konstatētas statistiski būtiskas atšķirības augsnes oglekļa uzkrājumā aramzemēs un ilggadīgajos zālājos. Attiecīgi, uzskaitot zemes lietojuma maiņu atbilstoši MRM datiem, nav jārēķina augsnes oglekļa uzkrājuma izmaiņas tajos gadījumos, kad fiksēta ilggadīgo zālāju transformācija par aramzemēm vai aramzemju transformācija par ilggadīgajiem zālājiem.
Understanding the spatial distribution of topsoil properties in grassland ecosystems is essential for improving soil ecosystem services, quality, and erosion resilience. The availability of free, high-resolution satellite imagery and advanced data mining techniques offers new opportunities for efficient soil property assessment. This study aimed to evaluate the potential utility of multi-season PlanetScope imagery to predict soil organic carbon (SOC), pH, and calcium carbonate (CaCO3). Using random sampling, 121 topsoil samples (0–30 cm depth) were collected with an auger across grasslands, bare soil, and eroded areas within a typical grazing land use. Three data mining techniques: random forest (RF), extreme gradient boosting (XGB), and support vector machines (SVM), were applied and evaluated using a 10-fold cross-validation. The results indicated that multi-season spectral covariates considerably improved the accuracy of the target soil properties compared to single-season imagery. SVM was the most effective algorithm for predicting SOC, achieving a root mean square error (RMSE) of 0.52%, mean absolute error (MAE) of 0.24%, and R² of 0.92. RF was the best-performing algorithm for predicting soil pH (RMSE = 0.22, MAE = 0.17, and R² = 0.97) and CaCO3 (RMSE = 0.55%, MAE = 0.42%, and R² = 0.96). While XGB failed to capture the variability in soil pH, the other models generated interpretable maps that accurately represented the distribution of soil properties across different land cover categories. The green-red vegetation index (GRVI) was the most critical covariate for predicting SOC, while elevation and the topographic wetness index (TWI) were key predictors for soil pH and CaCO3, respectively. This study underscores the potential of multi-season PlanetScope imagery for accurately predicting soil properties and recommends conducting similar studies in diverse geographical settings to validate these findings and develop more generalizable models.
The pollution of agricultural soil with potentially toxic elements (PTEs) becomes a global challenge. The mobility of PTEs is controlled by soil general characteristics; pH, organic matter (OM%) calcium carbonate (CaCO3%), and particle size distribution. This article aims to dedicate the impact of CaCO3 on the distribution of Cd and Pb in the Nile Floodplain soil in Egypt. In addition, the Index of Geoaccumulation (Igeo), Contamination Factor (CF), and Contamination Degree (CD) were applied to investigate pollution levels, while Ecological risk (Er) and Potential Ecological Risk Index (PERI) were used to assess the ecological risk of PTEs in the soil. The soil quality index (SoQI) model was applied to assess soil quality in the study area. The mean recorded values for pH, CaCO3, OM, Cd, and Pb were 8.28, 6.42%, 2.25%, 7.84 mg/kg, and 20.35 mg/kg, respectively. The role of CaCO3 in the distribution and content of Cd and Pb in the study area was statistically approved. The Igeo, CF, Er, CD, and PERI indicated that the study area is at very high risk, particularly due to the presence of Cd. The calculated SoQI value is 5, reflecting that the study area soil is at a very high risk class. The results imply that the study area is at high risk from PTEs. Fortunately, the presence of CaCO3 can significantly retain and reduce the bioavailability of Pb and Cd, hence reducing food contamination. Finally, it is recommended to use eco-friendly fertilizers and control the application of chemical fertilizers and pesticides.
The effect of soil carbon on the available water content (AWC) has garnered considerable attention. An increasing number of studies have recognized a beneficial impact of soil organic matter (SOM) on available water content (AWC); however, results are not consistent regarding the magnitude of soil organic carbon (SOC) effect on AWC. In particular, the critical SOC range necessary for enhancing AWC requires clarification. Accordingly, 165 samples were collected from four sites, where two sites received poultry litter (PL) and two sites did not, covering a wide range of carbon contents from low to high (4.5–22.9 g kg ⁻¹ ). The bulk density was the same, and the soils were tested for their field capacity (FC) and permanent wilt point (PWP) in the lab. The results revealed that there was no significant correlation between the clay and AWC, and a significant positive relationship between SOC and AWC was exhibited, suggesting that the increase in AWC mostly resulted from the increase in SOC. However, the AWC did not change significantly with increasing SOC when the SOC was below 10 g kg ⁻¹ , whereas a significant increase in AWC occurred when the SOC increased from 10 to 14 g kg ⁻¹ . The largest increment in AWC occurred when the SOC increased from 14 to 18 g kg ⁻¹ , but the increase in AWC with increasing SOC decreased when the SOC was above 18 g kg ⁻¹ . Thus, a critical range of SOC for AWC from 14 to 18 g kg ⁻¹ could significantly improve the soil water‐holding capacity. Additionally, most soil samples within the critical SOC range were collected from sites that received PL. Thus, this study also evaluated the enhancement of AWC by PL application, which efficiently improved the soil water‐holding capacity.
Soil organic carbon (SOC) is important in maintaining soil quality, fertility, and the terrestrial carbon cycle. Advances in technology have heightened global interest in estimating soil carbon sequestration. Assessing SOC stocks at landscape scales faces significant challenges, particularly in mosaic landscape influenced by anthropogenic and environmental factors. These challenges include the limited availability of high-resolution soil data, the high cost and labor intensity of soil sampling, and the difficulty of accurately representing soil heterogeneity using conventional sampling methods. This study investigates the influence of key landscape attributes including soil depth, land use type, slope gradient, and topographic position on SOC stock distribution and associated soil properties at 0 – 20 cm (topsoil) and 20 – 50 cm (subsoil) in the highlands of Cameroon. A total of 320 soil samples collected from a 100 km2 site were analysed in the laboratory. Results reveal that soil depth, land use type, and topographic position influence the distribution of SOC, bulk density (BD), and SOC stocks. Land use and topographic positions interactions significantly impact SOC, coarse fraction (CF), and SOC stocks, reflecting varied human activities and environmental effects across topographic locations. Total SOC stocks for the site are
estimated at 37,571 tons C/ha in topsoil and 57,341 tons C/ha in the subsoil, totalling 94,912 tons C/ha of carbon to a depth of 50 cm. Kriging maps demonstrate a decreasing trend in SOC stocks from west to east, with higher values in lowlands characterized by lower BD and CF, and lower values in mountainous areas. These
findings advance SOC stocks evaluation in the highlands of Cameroon, providing a foundational reference for future assessments to guide landscape restoration initiatives in ecologically fragile ecosystems.
Purpose
Floods are considered the major threat of soil suitability loss for agricultural purposes in floodplain agroecosystems. The present work questioned (i) how does the flooding affect soil of agricultural lands? (ii) can the mixing of deposited sediments with the covered soil be considered a suitable practice to keep soil functionality?
Materials and methods
The study was conducted in three croplands of Emilia–Romagna region affected by floodings in May 2023. The sampling concerned both the deposited sediments and the covered soil, then mixtures of deposited sediment and covered soil at 1:1 ratio (soil–sed) were also obtained. These samples were analysed for the main physicochemical properties, the water infiltration and the crusting index.
Results and discussion
The deposited sediments had a lower amount of nitrogen (-47%), organic C (-47%) and available phosphorus (-60%), and a higher silt content (+ 17%) compared to the covered soil. The obtained soil–sed had a lower amount of such nutrients than covered soil. Further, the higher silt content in soil–sed than in covered soil does not help the accumulation of such nutrients and lowered the water infiltration. The soil–sed had a higher crusting index (+ 24%) compared to the covered soil suggesting a higher probability of soil to promote surface runoff.
Conclusions
In the investigated study sites, the flooding had a marked effect on soil physical properties because of the higher silt content and the lower organic carbon content of deposited sediments compared to covered soil. To face such issues for allowing agricultural productivity, the addition of organic amendments can be suggested due their cost–effectiveness.
The words we choose to describe our research ultimately directs its course. A dominant term in soil science now, is ‘sequestration’, referring to the removal of carbon (C) from air and its irreversible seclusion in soil, ideally as stable soil organic carbon (SOC). An emerging view, however, now sees SOC as an inherently dynamic assemblage of forms, all potentially vulnerable to decay, with no discrete, measurable fraction holding C in ‘sequestered’ form. Rather than speaking of C ‘sequestration’, then, we might refer instead to SOC ‘stewardship’. This word, now, enfolds the entire spectrum of SOC, not merely some elusive ‘persistent’ or ‘stable’ fraction, perhaps redirecting inquiry; for example, does C need to be ‘sequestered’ in stable form for SOC to serve as effective repository of excess atmospheric CO2? ‘Stewardship’ explicitly accepts the relentless turnover of SOC, emphasizing the need to manage not only fixed stocks of C, but also the cyclical flows of C through ecosystems that drive their functions. Among other benefits, ‘stewardship’ might motivate us to consider all functions of SOC (not only climate mitigation), consider the entire C cycle (not only enhancing soil C), and preserve existing troves of SOC (not only augmenting them in selected places.) Perhaps most fundamentally, by its etymology, ‘stewardship’ poses a compelling, timeless question: for whom do we steward SOC? Asking why look after SOC, not only reflects our own underlying quest for resilience, but also expands our potential audience and entices the more creative minds that must succeed us. Although ‘stewardship’ may elicit new and fruitful inquiry, we may need to look for words even more evocative, more alluring, more true to our mandate of living well within the circling C that must always sustain us.
Plastik atıkların mikroplastik oluşumuna katkıda bulunan kaynaklar çeşitlidir ve kullanılmış ambalaj malzemeleri, bozunmuş tekstiller ve büyük plastik ürünlerinin parçalanması gibi faktörlerden meydana gelir. Bu plastikler, bir kere çevreye salındıklarında, abiyotik (canlı olmayan) ve biyotik (canlı) faktörler tarafından etkileşime girer ve mikroplastik formuna dönüşerek karasal ve sucul ekosistemlerde yaygın bir şekilde bulunur. Mikroplastiklerin çevresel etkisi uzun bir süredir bilinmekle birlikte, mikroplastik araştırmalarındaki artış, kaynakları, dağılımları ve potansiyel sonuçları daha detaylı bir şekilde anlama ihtiyacını öne çıkarmaktadır. Bu karmaşık sorunun ele alınması, çevre bilimleri, kimya ve ekoloji gibi alanlardaki uzmanlıkların disiplinlerarası işbirliğini gerektirir. Mikroplastik kirliliğini azaltma çabaları, geliştirilmiş atık yönetimi uygulamalarını, sürdürülebilir malzeme tasarımını ve bilinçli politika oluşturmayı içeren bütünlüklü bir yaklaşımı gerektirir. Bilimsel topluluk, plastik atıklardan mikroplastik oluşumunun karmaşıklıklarını çözerek, etkili kirlilik önleme ve çevre koruma stratejilerine rehberlik edecek kritik içgörüler sunabilir. Bu noktada, özellikle bilgi ve tecrübelerin etik çerçevede paylaşılmasına önem verilmeli ve akademik dürüstlük ilkelerine riayet edilmelidir. Mikroplastiklerin plastik atıklardan türemesi, çeşitli fiziksel ve kimyasal mekanizmalar tarafından şekillendirilen birçok katmanlı bir süreçtir. Bu süreçleri anlamak, mikroplastik kirliliğini sınırlama ve ekosistemleri koruma stratejileri geliştirmek için temel bir gerekliliktir. Mikroplastik araştırmalarının disiplinlerarası doğası, bilimsel alanları aşan bütünlük gerektiren bir yaklaşımı zorunlu kılar. Devam eden ve gelecekteki araştırma çabaları, mevcut metodolojilerin geliştirilmesine, metodolojik tutarsızlıkların ele alınmasına ve çalışmalardaki karşılaştırılabilirliği artırmak için standart bir çerçevenin oluşturulmasına odaklanmalıdır. Teknolojik ilerlemeler, sıkı metodoloji doğrulama ile birleştirildiğinde, mikroplastik tespiti ve analizi ile ilişkili karmaşık sorunların kapsamlı bir anlayışına ulaşmada önemli bir rol oynayacaktır. Bu derleme, mikroplastiklerle ilgili detaylı içgörüler sunarak, gelecekteki araştırmalar için metodolojiler önererek ve mikroplastik kirliliği sorununu ele almak için birleşik bir yaklaşımı savunarak özellikle Türkiye'deki mikroplastikler konusundaki tartışmaya önemli ölçüde katkıda bulunmayı amaçlamaktadır.
Digestate and its derived composts are valuable organic fertilizers for growing vegetables and field crops.
However, the impacts on enzymatic activities and microbial resources acquisition pattern are not well addressed.
This study investigated ecoenzymatic activities and microbial resource acquisition patterns following these
organic fertilizations for sunflower cultivation. The experiment involved applying digestate, five compost types
derived from digestate, and inorganic N fertilizer (NINORG), with a control plot having no treatment. Activities
of nine enzymes related to C-, N-, P-, and S- acquiring were measured at three development stages: seedling, preblooming,
and harvest. Across all treatments, resource allocations, especially for C-, N-, and P- acquisitions,
increased with plant development, correlating positively with microbial biomass, soil organic carbon, and soil
nutrients contents, showing the heightened energy and nutrient sources stimulated microbial growth, prompting
increased resource allocation to meet elevated demands, particularly in later crop developmental stages. Stoichiometric
analysis revealed greater investments in P compared to N and C, persisting throughout the study
period, with P acquisitions at least four-fold greater than N and at least seven times greater than C. This pattern
was greatly impacted at harvest for all treatments except NINORG and control, with a reduced investment rate
for P- acquisition compared to that of C-, N-, albeit the C: N:P ratio was still far short of the global mean 1:1:1
ratio. The strong negative correlation between available P and vector angle (p<0.001) indicated that the addition
of bioavailable P through organic amendments helped reduce the gap towards the ideal ratio. In summary, on
soils with imbalanced microbial nutrient and energy demands, organic amendments intensified microbial
growth, resulting in heightened nutrient acquisition. However, the declining trend in P acquisition rates
compared to C and N over the cropping period suggests possible adjustments with the help of organic fertilizations.
Organic fertilizers, by addressing energy-nutrient imbalances, can contribute to a healthier soil
ecosystem under conventional farming systems.
Temperate grasses conserve soil by providing vegetative cover and by favoring soil aggregation. A field study was conducted on a Charlottetown fine sandy loam (a coarse‐loamy, mixed, frigid Typic Haplorthod) to determine the effect of cultivars of orchardgrass ( Dactylis glomerata L.) and tall fescue ( Festuca arundinacea Schreb.), in comparison to timothy ( Phleum pratense L.), on soil structure and organic matter fractions after 4 yr of growth. Timothy is one of the main grasses grown in the cool humid climate of eastern Canada. Bulk density (1.27–1.32 Mg m ⁻³ ), pore‐size distribution, and shear strength (12.5–15.6 kPa), as a measure of soil structural form, were within the optimum range for this soil type under each grass species. Dry‐aggregate mean weight diameter (MWD) was similar (3.66–4.30 mm) among grass species. Wet‐aggregate MWD was greater under tall fescue cultivars and ‘Farol’ timothy (2.81–3.22 mm) compared with the orchardgrass and ‘Champ’ timothy (2.08–2.36 mm). These differences were also reflected by the difference or ratio of MWD between dry and wet sieving. Aggregate‐size distribution indicated that wet‐aggregate MWD differences were associated with greater levels of macroaggregates (>2 mm). Differences in water‐stable aggregate stability were not related to differences in plant parameters, organic matter, or organic matter fractions (i.e., microbial biomass C, carbohydrates, and particulate organic matter). These data suggest that organic matter parameters, commonly used to characterize soil stability in cropping systems, are less useful for soils under perennial grass with stable microaggregate structures.
The Permanent Rotation Trial at the Waite Agricultural Research Institute in South Australia was established on a red-brown earth in 1925, with predominately cereal-long fallow rotations on 34 adjacent plots. The trial was upgraded in 1948 to include a greater proportion of pasture leys in the rotations and currently contains 11 treatments. The trial is unreplicated; however, each phase of a sequence is represented each year. Seven of the original rotations have remained in an unbroken sequence since 1925: continuous wheat (W), wheat-fallow (WF), wheat-peas (WPe), wheat-pasture-fallow (WPaF), wheatoats- fallow (WOF), wheat-barley-peas (WBPe), wheat-oats-pasture-fallow (WOPaF). For the 11 rotations, soil organic carbon (SOC) in the top 10 cm declined from 2.75% in 1925 to a mean value of 1.56% in 1993. One plot, which had reverted to permanent pasture in 1950, showed the smallest decline with an SOC content of 2.46% in 1993. The greatest declines in SOC were in the 4 original rotations that included fallow phases in the sequence (mean value of 1.22%). In the WF rotation the SOC content had declined from 2.75 to 1.04% during 68 years of cropping. Associated yield decreases showed that the treatment could not sustain production. Soil organic C declined linearly with increasing frequency of fallows and decreasing frequency of pasture in the rotations. Average grain yields (1925-93) in the 7 original sequences ranged from 2.64 t/ha in WOPaF to 0.89 t/ha in the continuous W plot. The linear decline in yields for WBPe, WPaF, WPe, and WOF treatments indicate a convergence in the 1990s under current management, with an average yield of 1.54 t/ha in 1993 and average SOC in the top 10 cm of 1.32%. We hypothesise that the gradual increase in grain yields from the continuous W plot since the 1960s is the result of a gradual build-up of light fraction organic material, which assists in the maintainence of structure and nutrient availability.
A medium-term (10 years) stubble x tillage field experiment was established in 1984 on a red-brown earth at Tarlee, 70 km north of Adelaide, to develop a suitable system for sustaining the soil resource. Measurements of infiltration capacity, soil detachment rate, and erosion were taken in summer, autumn, winter, and spring 1989-90. The rotation was wheat-barley-grain legume, and treatments included 3 levels of stubble retention (0.5, 3.0, 5.0 t/ha.year) and 4 types of tillage [no-tillage (NT), direct drill (DD), reduced tillage (RT), conventional cultivation (CC)]. NT was seeded with narrow points (30 mm) and the other tillage treatments with wide shares (150 mm). The Northfield rainfall simulator with an erosive rainfall of 100 mm/h and an energy of 28.6 J/ m2.mm was used to measure runoff and soil and nutrient loss. This paper reports on erosion from this experiment. The results show that runoff was reduced through farming practices such as the retention of adequate stubble residue (about 3-5 t/ha.year of cereals), NT, or a combination of these factors. Increasing the average - - - annual stubble retention decreased runoff and soil loss linearly. The greater the amount of stubble retained annually, the less the runoff and soil loss, whether or not the soil surface was protected. The significant sediment release and soil loss from bared soil is inversely related to soil stability measured by a reduction in soil organic matter. Crop type also influenced erosion; for example, soil was more vulnerable to erosion after peas than after cereal. The amount of stubble after harvest was usually greater with cereals than with grain legumes. Runoff as a percentage of applied rain, and soil loss, ranged from 26 to 60% and 0.52 to 1 .I t/ha for 0.5 t/ha. year stubble (means of all treatments) for April 1989 and August 1990, respectively, and from 5 to 35% and 0.03 to 0.8 t/ha for 5.0 t/ha.year stubble for the same simulation period. Runoff rates in the last 3 min of 18 min simulation ranged from 0.4 to 1.1 mm/min for 5.0 t/ha.year stubble and from 0.8 to 1.7 mm/min for 0.5 t/ha.year stubble. The runoff rates recorded at the 18th minute of simulation ranged from 0.5 to 1.2 mm/min for NT and 0.7 to 1.5 mm/min for CC.
Chemical and physical degradation of Red Ferrosols in eastern Australia is a major issue necessitating the development of more sustainable cropping systems. This paper derives critical concentrations of the active (permanganate-oxidisable) fraction of soil organic matter (C1) which maximise soil water recharge and minimise the likelihood of surface runoff in these soils.
Ferrosol soils were collected from commercial properties in both north and south Queensland, while additional data were made available from a similar collection of Tasmanian Ferrosols. Sites represented a range of management histories, from grazed and ungrazed grass pastures to continuously cropped soil under various tillage systems. The concentration of both total carbon (C) and C1 varied among regions and farming systems.
C1 was the primary factor controlling aggregate breakdown, measured by the percentage of aggregates <0·125 mm (P125) in the surface crust after simulated rainfall. The rates of change in P125 per unit change in C1 were not significantly different (P < 0·05) for soils from the different localities. However, soils from the coastal Burnett (south-east Queensland) always produced lower P125 (i.e. less aggregate breakdown) than did soils from the inland Burnett and north Queensland locations given the same concentration of C1. This difference was not associated with a particular land use.
The ‘critical’ concentrations of C1 for each region were taken as the C1 concentrations that would allow an infiltration rate greater than or equal to the intensity of a 1 in 1 or 1 in 10 year frequency rainfall event of 30 min duration. This analysis also provided an indication of the risk associated with the concentrations of C1 currently characterising each farming system in each rainfall environment. None of the conventionally tilled Queensland Ferrosols contained sufficient C1 to cope with rainfall events expected to occur with a 1 in 10 frequency, while in many situations the C1 concentration was sufficiently low that runoff events would be expected on an annual basis.
Our data suggest that management practices designed both to maximise C inputs and to maintain a high proportion of active C should be seen as essential steps towards developing a more sustainable cropping system.
Measurements of bulk density, moisture retention, aggregate stability and shear strength were taken for sandy loam and loamy sand soils with different organic-matter contents ranging from 1.23 to 5.64%. Organic matter in soils originated from either being under grass treatment for some years or mixing two forms of peat each at 4, 11 and 17% rates to a control soil. Aggregate stability was measured by the percentage water stable aggregates (WSA) as well as individual aggregate energy (IAE) measured using single drop impact test. Organic matter from grass significantly increased percentage WSA from 2.15 to 21.62% and IAE from 4 to 33 mJ. While percentage WSA reduced significantly from 2.50 to 0.88 with increasing peat content, the IAE reduced only slightly from 3.93 to 3.45 mJ. This suggests that peat reduces the overall soil stability without affecting the strength of individual aggregates.Organic matter from both grass and peat reduced bulk density and increased moisture retention. While organic matter from grass increased soil shear strength from 19.17 to 24.44 kN m−2, that from peat reduced it from 15.47 to 11.90 kN m−2. The effects of both forms of organic matter on bulk density and moisture retention were expected to have reduced their strengths. However, since organic matter from grass improved aggregate stability, it reduced soil dispersion in water and improved shear strength, while peat only made the soil aggregates fall apart and reduced their shear strengths. The results from this study show that the influence of organic matter on soil shear strength depends on whether or not it improves soil aggregate stability.
Using data from long-term experiments at the Loess-Chernozem site, Bad Lauchstadt und 12 other European sites, the carbon (C) and nitrogen (N) dynamics in soils, the determination of decomposable soil organic matter (SOM), the effect on yield of SOM as well as carbon and nitrogen balances are discussed. Both C and N in SOM have to be divided into an inert and a decomposable fraction. the inert C is strongly correlated with clay content, while most changes in both C and N occur in the readily decomposable fraction. In the experiments considered the latter ranges between 0.2 to 0.6% C and 0.02 to 0.06% N. The annual changes of the C-org content amount only to about 0.01% C-org corresponding to 500 kg/ha, even under extreme changes of the fertilizing system. Hot water extractable C(C-hwe) has proved to be an appropriate criterion for the calculation of the decomposable C and thus for the N release from soil. different methods to maintain a SOM balance are compared and first guideline values for an agronomically and ecologically justified SOM content of arable soils are recommended. In arable soils the exceeding of an upper C-org value influences neither crop yield nor the C and N balance in a positive way. In terms of ecology and environment, set-aside-programmes or fallows in a crop rotation affect the balances negatively. Atmospheric N deposition can amount to about 50 kg/ha.yr.
Zero tillage management reduces soil exposure and disturbance and, therefore, may improve soil aggregation and organic matter sequestration under some environments. We determined the distribution and soil organic C (SOC) content of five water-stable aggregate (WSA) classes at depths of 0-50, 50 125, and 125-200 mm in a loam, a silt loam, a clay loam, and a clay soil managed for 4-16 yr under conventional shallow tillage (CT) and zero tillage (ZT) in the Peace River region of northern Alberta and British Columbia. Macroaggregation (>0.25 mm) and mean weight diameter (MWD) were greater under ZT than under CT in coarse-textured soils at a depth of 0-125 mm. Under CT, macroaggregation and MWD increased with increasing clay content, thereby reducing the potential of ZT to improve these properties in soils with high clay content. Concentration of SOC tended to be greatest in macroaggregates and lowest in microaggregates of coarse textured soils, but was not different among WSA classes of fine-textured soils. Soil organic C content of macroaggregates under ZT was 0.34, 0.40, 0.62, and 0.16 kg m-2 greater than under CT at a depth of 0-200 mm in the loam, silt loam, clay loam, and clay soil, respectively. Our results suggest that implementation of ZT in this cold semiarid climate can quickly improve WSA of coarse-textured soils and potentially increase SOC sequestration, albeit more slowly than in warmer more humid climates, when macroaggregation is improved.
Municipal solid waste (MSW) compost contains large amounts of organic matter that can be beneficial to soil. The objectives of this study were to measure N mineralization and acid hydrolyzable N in soil amended with MSW compost and correlate corn (Zea mays L.) grain yield with acid hydrolyzable N. The soil, an Orthic Black Chernozem (Entic Hapludoll) cropped to corn, was amended with composts at either 90 dry Mg ha-1 yr-1 from 1993 to 1995, or at 270 dry Mg ha-1 in one application in 1993. Soil samples were collected in the fall of 1994 and 1995 to measure C and N mineralization and acid hydrolyzable N. Potentially mineralizable N was estimated with the NCSOIL model after using C and N mineralization observed in the laboratory to calibrate the model. Net N immobilization occurred in compost-amended soils collected in 1994 with less than 0.2% of the total soil N mineralized in the compost treatments. In 1995, there was net mineralization in compost treatments but less than 5% of total soil N mineralized in 120 d. The addition of compost increased the acid hydrolyzable N of soil with 43-63% of the total soil N being acid hydrolyzable. Acid hydrolyzable soil N did not correlate to N0 but weakly correlated with corn grain yield. The MSW compost source was more important than the timing of application in inducing differences in soil biochemical properties.
Using data from long‐term experiments at the Loess‐Chernozem site, Bad Lauchstädt und 12 other European sites, the carbon (C) and nitrogen (N) dynamics in soils, the determination of decomposable soil organic matter (SOM), the effect on yield of SOM as well as carbon and nitrogen balances are discussed. Both C and N in SOM have to be divided into an inert and a decomposable fraction. The inert C is strongly correlated with clay content, while most changes in both C and N occur in the readily decomposable fraction. In the experiments considered the latter ranges between 0.2 to 0.6% C and 0.02 to 0.06% N. The annual changes of the C org content amount only to about 0.01% C org corresponding to 500 kg/ha, even under extreme changes of the fertilizing system.
Hot water extractable C (C hwe ) has proved to be an appropriate criterion for the calculation of the decomposable C and thus for the N release from soil. Different methods to maintain a SOM balance are compared and first guideline values for an agronomically and ecologically justified SOM content of arable soils are recommended. In arable soils the exceeding of an upper C org value influences neither crop yield nor the C and N balance in a positive way. In terms of ecology and environment, set‐aside‐programmes or fallows in a crop rotation affect the balances negatively. Atmospheric N deposition can amount to about 50 kg/ha·yr.
The purpose of this study was to determine whether green manure used either in rotation or intercropped with corn could increase soil organic-matter levels and improve soil physical conditions. Eight treatments were applied for a 3-year period to a Bear brook clay and a Franklin gravelly loamy sand in a rotation experiment. Aggregate-size distribution, bulk density, moisture retention, and water flow were measured for each soil. Green manures tended to increase organic-matter levels on the Bearbrook site over the three years of the experiment, although the increase was not statistically significant. On the Franklin site, no increase in organic-matter levels due to treatment was noted. Incorporating red clover into the Bear brook soil improved dry-aggregate distribution and reduced bulk density but did not increase the stability of aggregates in water. Infiltration did not improve in response to green manuring. Incorporating common vetch or buckwheat into the Franklin soil did not affect any physical parameter differently from the monoculture-corn treatment though a laboratory study suggested that buckwheat residue was more suitable than vetch residue for producing aggregates. Row cropping in general proved deterimental to the physical condition of this soil.
In the hierarchical model of soil aggregate formation proposed by Tisdall and Oades (1982), a major mechanism involved in the binding of microaggregates into macroaggregates is physical entanglement by roots and mycorrhizal fungus hyphae. Using data collected from soils of a chronosequence of tallgrass prairie restorations and an adjacent prairie soil cultivated to row crops for at least 100 yr. it was found that root lengths by diameter size class, the lengths of roots colonized by mycorrhizal fungi within each root-size class, and extraradical hyphal lengths of mycorrhizal fungi were all highly correlated with the geometric mean diameter (GMD) of water-stable soil aggregates. To better understand the relative contributions of roots and mycorrhizal fungi to water-stable aggregation, a conceptual model emphasizing the interrelationships between roots of differing size classes, mycorrhizal fungi and aggregate-size distribution was developed and evaluated using path analysis. From path analysis, it was found that extraradical hyphal length followed by fine (0.2–1 mm dia) root length had the strongest direct effects on GMD. It was expected that a physical entanglement mechanism would involve the very finest roots; however, the direct path between very-fine (<0.2 mm dia) root length and GMD was not significant. Although both root-size classes exhibited significant indirect effects on GMD via the relationships between their colonized lengths and xtraradical hyphal length, the overall effect of fine root length on GMD was much stronger than the effect of very-fine root length. To determine the relative influences of plant lifeforms on root morphology and estimate the effects of various lifeforms on GMD, data on aboveground standing crops associated with the root and fungus data were added to the path model. Prairie grasses were associated with both fine and very-line root lengths and exhibited the strongest effects on GMD; whereas, non-prairie grasses were most strongly associated with very-fine root length and only weakly affected GMD. Perennial species of Compositae were associated with line root length and also had a fairly strong influence on GMD. This study supports the conceptual model developed by Tisdall and Oades and suggests that a better understanding of soil aggregate development may be achieved by considering the interactions between roots and mycorrhizal fungi in relationship to plant community composition.
Soils were dispersed and separated into sand, silt, and clay frac- tions that were reconstituted to give mixtures of each soil with 5 to 40% clay. In the range from 0 to 35% clay, higher clay contents resulted in greater stability. Rate of cohesion recovery was over 10 times as fast at 90°C as it was at 23°C, showing that the processes Involved are physical-chemical rather than biological. Maximum rates of cohesion recovery occurred at moderate soil water tensions, prob- ably because some tension is needed to pull the particles into direct contact, but a continuous water phase is also essential to allow dif- fusion of bonding agents to the contact points. Since diffusion rates in water increase 3e0o*, while rate of cohesion recovery increased 1000% when temperature was raised from 23 to 90°C, other factors, such as higher Mobilities at higher temperatures of compounds contributing hooding ions to the solution. probably play a role In the rate of cohesion recovery. Recovery of cohesion was more rapid in the soil with organic C contents of 0.004 kg/lig than in the soil with 0.012 kg/kg. When the organic matter was removed with H 20 1 from the soil with 0.012 kg C/kg, its rate of cohesion recovery in- creased. Rate of cohesion recovery of this high organic matter soil was also increased by aging it at 0.1 kg HP/kg soil compared to 0.2 kg/kg. A possible explanation is that organic coatings, tending to prevent direct contact and bonding of adjacent projections of min- eral surfaces, are forced away from contact points by extremely strong forces that pull the adjacent minerals together when soil water ten- sions are high. When the higher organic matter soil had been con- solidated by air-drying and rehydrated, its rate of cohesion recovery was just as rapid as that of the soil with low organic matter.
Soil from a long-term crop rotation study conducted at Lethbridge, Alberta was analyzed to determine the influence of various spring wheat rotations with and without perennial forages on total and mineralizable soil organic matter contents. Crop rotations considered included: continuous wheat (W), fallow-wheat (FW), fallow-wheat-wheat (FWW), and fallow-wheat-wheat-forage-forage-forage (FWWAAA) in which the forage was a mixture of alfalfa and crested wheat grass. The organic C and N contents of soil after 33 yr of cropping were highest in treatments W and FWWAAA, and decreased with increasing frequency of fallow in the rotation. The inclusion of the perennial forage in the rotation did not increase organic C and N levels above those observed in the continuous wheat treatment (W). Differences in levels of mineralizable organic matter among treatments, as measured in laboratory incubations, were much greater than differences in total organic matter content among treatments. In the surface soil layer (0–15 cm...
Yield of corn (Zea mays L.) was measured at eight sites in 1982 and nine sites in 1983 on areas in farm fields exhibiting differing degrees of past erosion. Yield was also measured on depositional areas in some fields. Yield on depositional areas was, on average, marginally greater than on noneroded areas. Yield on severely eroded areas (all or most of original solum lost) ranged from 16 to 80% of that on noneroded areas with an average of 59%. There was little or no reduction in yield until the depth to Ck had been reduced to almost 50% of that on the noneroded profile. With further reductions in depth to Ck, yields declined rapidly on most sites. The primary cause of yield reduction varied from site to site and included reduced stand and seedling vigor due to a poor seedbed condition, nutrient deficiency and reduced available water holding capacity (AWHC). The impact of erosion on yield at a field and regional level was estimated based on the extent of erosion determined from aerial photographs and the site-specific yield measurements. Estimated corn yield on two fields was about 92% of that expected if no erosion had occurred. In a 90-km ² area of the Regional Municipality of Waterloo, 18% of the cultivated land was estimated to be moderately to severely eroded. Based on the site-specific yield measurements, this erosion would result in a 3.6% reduction in average corn yield in the region. The implications of the findings on preventative and remedial measures and on future productivity in the region are discussed. Key words: Erosion, yield, corn, seedbed condition, nutrient deficiency, water stress
Successful reduced tillage systems depend on suitable soil types and the maintenance of optimum soil structure. Studies were conducted to assess the tillage requirement of some well-drained Podzolic and Luvisolic soils in Prince Edward Island and their suitability for direct drilling. Relatively high amounts of silt and fine sand indicated that the soils were structurally unstable with a propensity for compaction. Compactability was inversely related (r ² = 0.90) to concentrations of soil organic carbon over a range of 0.2–2.0%. In the Ap horizons, where organic carbon exceeded 1.6%, the level of macroporosity (equivalent pore diam. > 50 μm) was generally greater than 10%. The B horizon and lower level of the Ap horizon, generally, had low porosity and organic matter, although pore continuity was adequate. Macroporosity was closely related to soil bulk density (r ² = 0.81). Penetrometer resistance down the soil profile indicated a relatively shallow rooting depth potential of 25–40 cm. A 3-yr direct drilling study with spring cereals illustrated that some degree of soil loosening is required to maintain optimum soil structure. Soil limitations for direct drilling were mainly low resistance to compaction combined with low potential for regeneration of soil structure. The possible implications of the soil physical properties are discussed in relation to the use of direct drilling within the short-term rotational mixed farming systems of Prince Edward Island. Key words: Soil structure, macropores, Podzolic soils, Luvisolic soils
Soil surface conditions improve with increased organic matter (OM) and water-stable aggregation (WSA), but surface variability may influence values obtained when soils are sampled to evaluate these factors. My hypothesis was that cultural operations for sorghum [Sorghum bicolor (L.) Moench] grown on ridges produce zones of differing soil OM and WSA. Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) was sampled at the 0- to 4-cm depth in furrows, on ridge tops, and on ridge sides before and after planting, after reforming ridges, and after harvest in 1992. Tillage (conventional [CT] and ridge [early (RT-E) or late (RT-L) stalk shredding]), position, and crop cycle (sampling) stage affected OM and WSA. Compared with ridges, OM in furrows was greater due to residue accumulations. Mean WSA was greater on ridges with CT than with RT-E or RT-L because disk-bedding to build the CT ridges moved more stable aggregates to ridges than the other treatments. More thorough mixing of residues by CT may have been involved also. Ridge and furrow positions and possibly ridge sides require separate sampling for obtaining representative OM and WSA data from ridge-tilled soil, especially where ridge tops are cleared at planting. Ridge clearing at planting should be limited to avoid residue reduction and lowered WSA that could lead to soil crusting and impaired seedling emergence.
Limited information exists on the methods used to compute the changes in wet aggregate stability, WAS, with time subsequent to changes in management practices. The objectives of this study were to: (i) develop a model to compute the net gain in WAS, WAS net , with time subsequent to the introduction of forages, (ii) assess the model using data from different soils, and (iii) determine the influence of soil properties on the regeneration of WAS. Stability measurements were made at monthly intervals during the 1989, 1990, and 1991 growing seasons from seven different soils under continuous conventional corn ( Zea mays L.) and forage treatments established in 1989. The interaction of cropping treatment, time of sampling, and gravimetric soil water content, θ, at sampling was significant for six out of seven soils at P = 0.05. Using the relation between WAS and θ and the changes in WAS with time, a semiempirical model was developed to predict WAS net . The model parameters described (i) the duration of delay before any observable changes in WAS occurred, (ii) the rate at which WAS increased from an initial to a maximum value, and (iii) the maximum potential change in WAS. The R ² for the best fit of the model ranged from 0.31 to 0.72 for the seven soils. The projected half‐life for WAS net , computed using the 3‐yr data, ranged from 4.52 yr for a clay loam to 7.75 yr for a sandy loam. Pedotransfer function analysis indicated that WAS net increased with increasing clay and organic matter contents and pH of soil. The model parameters and the associated pedotransfer functions were useful in assessing the influence of soil properties on stability following changes in management practices.
The objective of this study was to measure the effect of management-induced changes in soil organic carbon (OC) concentration on soil characteristics affecting the available water capacity. Four sites each of moderately coarse (sandy), medium, and moderately fine or fine (fine) soils were sampled within each of two cropland management systems and each of two virgin grassland management systems. Bulk density decreased with increasing OC concentration, and was greatest in sandy and least in the medium-textured soils. For all soils combined, a change in sand fraction accounted for about 75% of the change in water concentration by weight. An increase in OC concentration did not change the available water capacity in the sandy group and decreased it in the medium and fine textural groups. Loss of soil productivity induced by erosion in the northern Great Plains is probably not associated with a change in available water capacity. -from Authors
The purpose of this study was to determine the relationships among surface soil removal and additions of nitrogen (N) and phosphorus (P) fertilizer on spring wheat yields and yield components. Soil was mechanically removed from the surface of a Williams loam to 0.00-, 0.06-, 0.12-, and 0.18-m depths in a spring wheat fallow rotation. Three levels of N and three levels of P were applied in all combinations to each soil removal treatment prior to seeding a spring wheat crop. Study results are discussed. The data suggest P was the most limiting nutrient and additions of N fertilizer without P resulted in small yield increases.
Regression analyses were used to correlate organic matter, texture and surface area values to the cation‐exchange capacity (CEC) of clay‐rich soils in the lowlands of Quebec. The Ap, Bg and Cg horizons of 11 Gleysolic soils (Aqu‐Suborders) were analyzed for CEC, exchangeable bases and acidity, total and fine clay contents, organic matter, surface area and mineralogical composition. The soils contained illite, chlorite, smectite, and vermiculite in addition to quartz and feldspars. In the Ap horizon, total clay ( r = 0.815**) and fine clay ( r = 0.841**) contents were better related to CEC than organic matter ( r = 0.566**) and surface area ( r = 0.570**). In the Bg and Cg horizons, surface area ( r = 0.918** and 0.814**) gave the best correlation with CEC. As calculated by multiple regression equations, CEC values of organic matter increased with depth from 56.5 to 223 meq/100 g, while CEC values of total clay decreased from 37.7 to 22.5 meq/100 g and that of fine clay decreased from 57.5 to 50.7 meq/100 g. Variations in the mineralogical composition, although small, were sufficient to explain nearly 50% of the variations in the CEC. Clay mineralogy is important to predict the CEC of such soils where the contribution of clay is 3.5 to 5 times greater than that of organic matter.
Cation exchange capacities of Irish soils developed from a wide range of parent materials were found to be highly correlated with organic matter content and specific surface but not with clay content. Multiple regression analysis showed that organic matter in combination with specific surface accounted for 97% of the variation in CEC whereas organic matter and clay content only accounted for 58% of the variation. The better correlation between CEC and specific surface than between CEC and clay content, is attributed to the ability of surface area measurements to reflect the presence of phyllosilicates in silt and sand fractions of soils and to the fact that these minerals have less variable surface charge densities than cation exchange capacities. It is proposed that specific surface provides a better estimate than clay content, of the mineral component of CEC for soils of varying mineralogy.
The effect of periodate followed by sodium borate treatment on the stabilities of prewet soil aggregates has been determined by a permeability technique and by wetsieving. The effect of periodate treatment depends on the history of the site, the depth, and the great soil group from which the sample is taken. The stabilities of aggregates from various Red Brown Earths were all reduced by periodate treatment. The reduction was small for samples from plots which had been under pasture for many years, but very large for samples which had been under pasture for 4 years or less, or which were continuously cropped. The stabilities of all subsurface samples of the Red Brown Earths were completely destroyed by periodate treatment. Aggregates taken from a Solonized Brown soil were much less sensitive to periodate treatment, and those taken from a Rendzina were with one exception unaffected. These soils contain free CaCO 3 . It is probable that the most important function of the periodate treatment is to cause breakdown of the polysaccharides and polyuronides in the soil, and the results show that in cropped soils and soils under young pastures aggregate stability is primarily due to these materials. In soils under older pastures, or soils which contain free CaCO 3 , other materials prevent aggregate breakdown.
Percolation stability (PS) measured in a simple laboratory test with air-dried 1 to 2-mm aggregates correlates closely with surface roughness, decay and erosion. The processes involved in this test and the influence of soil properties on PS were studied. Air entrapment was the major cause of aggregate disintegration. Shear forces of the percolating water (10(-1) Pa), however, scarcely contributed to aggregate breakdown, although they can be one order of magnitude larger than forces of sheet flow on the soil surface. Percolation stability is a superior stability indicator for erosion studies. It is simple, needs little labor, soil, or equipment, results are highly correlated with soil loss, and, most importantly, they can be interpreted physically. The PS of 113 arable topsoils was inversely related to pH/(organic matter) or linearly to (14-pH) x (organic matter) with r(2) = 0.72 in both cases. Both regressions indicate an increase in stability with increasing organic matter content and decreasing pH. The influence of pH increases with increasing organic matter content. The decrease in stability with pH argues against liming to reduce surface crusting. This result is also supported by findings of other authors.
The objective of this study was to develop a procedure to predict the maximum potential amount of clay dispersible from soils during wetting. Information in the literature on the relationship between soil water content at sampling (THETA) and dispersible clay (DC) and that between THETA and wet aggregate stability for 10 different soils was used to develop extrapolation equations. The THETA at which DC became maximum (defined THETA(max)) ranged from 0.34 to 0.54 kg kg-1, and it increased with increasing clay and organic matter contents (R2 = 0.56). The DC(max), defined as the amount of clay that will disperse at THETA(max), ranged from 3.22 to 20.05 g clay 100 g-1 soil. The DC(max) increased with increasing clay and decreasing organic matter contents (R2 = 0.92). Decreases in organic matter content brought about larger increases in DC(max) in a clay soil than in a loam.
Temporal changes in the surface aggregate stability of an Oxic Paleustalf under different tillage practices (direct drilled/stubble retained versus conventional cultivated/stubble burnt) and under different crops (wheat (Triticum aestivum L.) versus lupin (Lupinus angustifolius L.)) were monitored at a 10-year-old rotation site in Wagga Wagga, N.S.W., Australia.Seasonal fluctuations in aggregate stability were observed under all treatments and were greater than the differences detected between the different tillage and cropping treatments. The seasonal variation was significantly related to the soil water content at the time of sampling and the lowest stability occurred during the autumn/winter period. Cropping under direct drilling and stubble retention resulted in significantly higher stability and lower seasonal fluctuations in stability than under conventional tillage and stubble burning. Despite the seasonal fluctuation, water stability over the season of both of the macroaggregate (more than 250 μm) and microaggregate (less than 50 μm) fractions increased significantly.While the mean (temporal) stability of the different treatments was significantly related to the mean organic carbon content (r = 0.91) and polysaccharide content, the temporal changes were not related to the soil organic carbon content nor the living root length density.Lupin had a more beneficial effect on promoting macroaggregate stability than wheat under the conventional tillage/stubble burnt treatment but no significant difference was found under the direct drilled/stubble retained treatment.
The main limitations to crop growth posed by restored opencast mine land derive from physical changes in the soil. The loss of soil structure makes the land prone to waterlogging and reduces soil workability. For spring cereals the main soil-management problem will be the production of an adequate seedbed. An experiment was therefore conducted on a clay loam soil to examine three alternative cultivation regimes for spring-barley production, these regimes contrasted autumn and spring ploughing and a tined cultivation on unmined land and restored land with and without drainage.Final yields were found to be determined by final ear numbers. This in turn derived from the initial plant population established, which varied with aggregate size distribution in the seedbed tilth. Unmined land produced more favourable tilths and hence higher yields, than either restored site irrespective of the tillage system. On all sites, autumn ploughing produced finer tilths than either spring working treatment. These trends persisted over 4 years and the tilth on all sites deteriorated over this period, though most noticeably on the unmined land. The stability of seedbed aggregates was correlated with soil organic-matter content, which varied across sites. Straw incorporation over 4 years was found to give only a minor enhancement of soil organic-matter concentration over straw burning. This difference did not noticeably affect crop yields or soil aggregation.
To determine the effect of soil organic matter on concentrations of metals in soil solution and their extractability from soil, solutions containing varying concentrations of Mn, Zn and Cu salts were added to five samples of a sandy loam soil with organic matter levels ranging from 0.8 to 2.4% C. Concentrations of the metals and their ions in solutions displaced from the samples after 3 weeks of incubation were determined. Extractabilities of the metals by both single extractants (EDTA and acetic acid) and by a sequential extraction scheme (calcium chloride, hydrogen peroxide, acetic acid and aqua regia), and release of the metals into solution as a function of pH were also studied.
The effects of organic matter and particle-size distribution on the available-water (Avf) and retained-water capacities (θvf(0.05)) of 144 surface and subsurface horizons, from 77 west Midland soil profiles was investigated by regression analysis using GENSTAT. A large proportion of the variation in both Avf and θvf(0.05) is explained by differences in organic carbon content. Multiple regression equations incorporating organic carbon, clay and/or silt content explain between 74 and 77% of the variation in θvf(0.05) and between 49 and 57% of the variation in Avf. The practical implications of these results with respect to the management of soils are discussed.
Data on rates of change in wet-aggregate stability under different cropping systems were used to infer rates of change in the amount of stabilizing materials present. Increases in wet-aggregate stability did not correlate with increases in total organic carbon content, suggesting that some components of the organic carbon pool are more actively involved in stabilizing aggregates than others. Assuming a linear relation between these active components and wet-aggregate stability, the amount of stabilizing materials present should increase exponentially with time when forages are introduced onto soil previously used for row crop production. -Authors
The positive effects of soil organic matter (OM) on soil properties that influence crop performance are well documented. But definitive and quantitative information of differential effects of soil OM contents is lacking for the northern Great Plains. The objective of this study was to quantify the contribution of a unit quantity of soil OM to productivity. Experiments were conducted on Williams loam (fine-loamy, mixed, Typic Argiboroll) for 4 yr in the same field. The variables were soil OM content of the upper 30.5 cm together with all combinations of three postplanting soil available N levels (55, 90, and 125 kg N ha-1 as NO3-N to 1.2 m) and three water levels. Water levels were uniformly maintained with a trickle system that independently metered water to each plot for each soil available N level. Pretillering spring wheat (Triticum aestivum L.) plant population decreased as soil OM content decreased in 3 of 4 yr. On an annual basis, highest total aerial dry matter and grain yields were associated with highest OM contents. The contribution of 1 Mg OM ha-1 to soil productivity, across the range of 64 to 142 Mg OM ha-1, was calculated as equivalent to 35.2 kg ha-1 for spring wheat total aerial dry matter and 15.6 kg ha-1 for grain yield. Loss of productivity associated with a depletion of soil OM in the northern Great Plains is primarily a consequence of a concomitant loss of fertility.
The relative importance of diverse factors affecting aggregation in four Wisconsin soil types was studied by multiple regression analyses. Single and combined effects of pH and contents of organic matter, microbial gum, clay, and free iron oxide were considered.
In general the most important single factor was the microbial gum. However, in the Kewaunee soil which has a relatively high content of clay and iron oxide, the iron oxide was of prime importance in aggregate formation. In all the soils, iron oxide showed a marked effect on aggregation with a tendency to be more important in the smaller aggregate size range. The effect of clay, however, was very small with the exception of the high clay soil (often > 30% clay), in which its effect was only exceeded by that of the free iron oxide. In the multiple correlation analysis the effect of organic matter was considered separately from that of microbial gums. By this statistical analysis only a slight positive relationship existed between organic matter and soil aggregation, i.e., the effect of organic matter was conditioned largely by its content of microbial gum; pH 6.5 was optimum. No relationship existed between soil aggregation and the rate of decomposition of organic matter as measured by CO 2 evolution from the soil.
This study examines the cumulative effect of erosion on soil properties that are important to productivity, and estimates the effect of erosion on grain yields. The impact of varying degrees of erosion on productivity was estimated by adding back incremental depths of topsoil to eroded knolls. Grain yields were increased by 45-58% by adding 50 mm of topsoil, with additional topsoil (100 or 150 mm) generally increasing yields slightly, but at a decreasing rate. Changes in soil quality with increasing erosion were measured on otherwise similar soils on eroded knolls, with the period of cultivation ranging from 0 (native) to 75 yr. Reductions in the amount of 137Cs in surface horizons with increasing period of cultivation indicated the cumulative effects of erosion, with general soil losses of 20 to 30 Mg ha-1 yr-1. Consistent reductions in silt plus very fine sand fractions with time suggested that wind erosion had been dominant. -from Authors
Slow water infiltration in some California soils results in considerable irrigation water loss through increased runoff and evaporation. This 25-1110 study was conducted to evaluate the effects of different organic amendments on soil physical parameters and water infiltration rates on an irrigated soil. Incorporation of three loadings (25 Mg ha⁻ each) of poultry manure, sewage sludge, barley straw (Hordeum vulgare L.), and alfalfa (Medicago sativa L.) to an Arlington soil (coarseloamy, mixed, thermic Haplic Durixeralf) for 2 yr increased soil respiration rates (139-290%), soil aggregate stability (22-59%0), organic C content (13-84%), soil saccharide content (25-41%), soil moisture content (3-25%), and decreased soil bulk density (7-11%). The change in soil physical properties resulted in significantly increased cumulative water infiltration rates (18-25%) in the organic-amended plots as compared with the unamended plots. Although additions of poultry manure and sewage sludge contributed to higher soil organic matter compared with straw and alfalfa, the straw amendment was statistically more effective in increasing soil aggregate stability, total saccharide content, infiltration rates, and soil respiration rates and in decreasing bulk density in the tillage zone. The increase in cumulative infiltration rates measured with the first organic addition (April 1987–January 1988) were significantly correlated with increased soil aggregation (P ≤ 0.01). Cumulative infiltration rates during the second (February 1988–September 1988) and third (October 1988–May 1989) organic incorporation were signficantly correlated with decreased bulk density (P ≤ 0.01), but not with aggregate stability. Multiple linear regression analyses indicated that water infiltration rates in the organic-amended soils were initially increased by stimulation of microbial activity, which increased the stabmty of soil aggregates. Cumulative infiltration rates were further increased by a decrease in soil bulk density with additional organic treatments to the tillage zone.
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A Nigerian lignite sample was analyzed for its nutrient element and organic components. The effect of two oxidation procedures, namely, oven‐oxidation and wet‐oxidation on the composition and extractability of organic fraction with 0.1 M sodium hydroxide (NaOH), was also studied. A pot experiment was conducted to investigate effect of the oxidized lignite samples on the growth of Gmelina arborea seedlings. The lignite sample is very acidic in reaction with a pH of 2.0, and has low quantity of macro‐ and micronutrient elements with a carbon (C):nitrogen (N) ratio of 103. It, however, has over 90% organic matter with more than 78% extractable humic substances. All these components were either increased, decreased, or unaffected by the oxidation pretreatments. Compared to the control, both the unoxidized and differently oxidized lignite samples, generally depressed growth of 12‐week‐old Gmelina arborea seedlings in the Alfisols while their addition to the Oxisols enhanced the growth of the seedlings. Wet‐oxidized lignite stimulated growth of the seedlings more than either unoxidized or oven‐oxidized sample while the latter performed the poorest of the three.
Laboratory studies to assess the effects of pH, and phosphorus (P) and organic matter contents on zinc (Zn) distribution in various soil fractions were conducted. Soils were incubated with different levels of lime, P fertilization, and two types of added organic materials. Phosphorus and pH were found to influence Zn distribution in the different soil fractions. Increase in pH and P decreased available and organic Zn and increased unavailable forms. Where fresh Zn was applied, a greater proportion of Zn was retained in the available and organically‐bound Zn forms. Application of maize stover and cow manure had a temporal effect of reducing available zinc in both the Chiota and Gwebi soils. The organic Zn and other unavailable forms of Zn increased showing that Zn was being immobilised. The immobilization was a relatively rapid process occurring in the first two weeks. The release of Zn which had been immobilised increased with time of incubation.
The structural stability of 32 cropped soils in the northwest Iberian peninsula was compared with that of pasture and woodland soils in the same region using Emerson's test and a rain simulator. The cropped soils were found to be less stable, largely because of the reduction in organic matter content due to cropping. Stability was also favoured by high concentrations of aluminium oxides bound to organic matter, and weakened by high pH. The latter relationship is hard to explain on the basis of the data obtained in this study; it is suspected that structural stability and soil pH are influenced by some third factor linked to farming practices (applied fertilizer levels, use of heavy machinery, etc.).
Soils from fifteen field experiments in the United Kingdom and one in France that compared direct drilling with mouldboard ploughing were examined with respect to their composition and physical properties. Indices of the stability and shrinkage of soil aggregates were obtained by measurement and an index of compactability was derived from an established relationship. It was hypothesized that these properties were possible determinants of soil responses to zero-tillage.Aggregate stability and shrinkage were correlated with organic carbon and clay content, respectively. Organic matter contents were greater at the surface of direct-drilled soils than in the complete topsoil layer after direct drilling or ploughing. In some cases the increase in organic matter significantly improved the physical properties of the soils.The three indices, of stability, shrinkage and compactability, were each ranked in high intermediate or low groups, and the soils classified according to their ratings in these groups. The resulting classification broadly agreed with a previous one of soil suitability for sequential direct drilling mainly based on experimental agronomy.
Data are assembled from the Rothamsted classical field experiments on the effects of long-continued cropping and manuring on the amount of organic matter in soil, on the age of this soil organic matter, on the amount of microbial biomass in the soil, and on the rate at which plant residues decompose in these soils. These data were then fitted to a model in which soil organic matter was separated into five compartments: decomposable plant material (DPM, half-life 0.165 years); resistant plant material (RPM, 2.31 years); soil biomass (BIO, 1.69 years); physically stabilized organic matter (POM, 49.5 years) and chemically stabilized organic matter (COM, 1980 years) For unitary input of plant material (1 t fresh plant C ha-1 year-1) under steady-state conditions, after 10,000 years, the model predicts that the soil will contain 0.01 t C in DPM, 0.47 t in RPM, 0.28 t in BIO, 11.3 t in POM, and 12.2 t in COM. The predicted radiocarbon age is 1240 years (equivalent age). The fit between predicted and measured data is sufficiently good to suggest that the model is a useful representation of the turnover of organic matter in cropped soils.
(C) Williams & Wilkins 1977. All Rights Reserved.
To investigate the contribution of organic matter to the cation exchange capacity (CEC) and the specific surface area (SSA) of organomineral complexes in soils, we studied A horizons of four soils (two Hapludalfs and two Argiudolls) in central Iowa. The effect of mineralogy on CEC and SSA was held nearly constant by sampling soils developed in the same parent material (loess) and landscape position (summit). A range of organic matter contents was obtained by variations in native vegetation, the effects of cultivation, and horizon depth. The CEC, SSA, and organic C content of unfractionated samples were determined. Soil samples were also separated into coarse silt, fine silt, coarse clay, and fine clay size fractions after dispersion by sonification. The organic C content of each fraction was determined, as were CEC and SSA, before and after peroxide treatment. Multiple linear regression equations were developed to relate CEC and SSA to organic C and peroxidized SSA. Partial regression coefficients suggested that the net contribution of organic matter to the CEC of unfractionated soil materials was 184 cmol(+) kg-1 of organic C. In the coarse silt, fine silt, and coarse clay fractions, organic matter was estimated to contribute approximately 559 cmol(+) kg-1 of organic C to the CEC and 7.22 x 105 m2 kg-1 of organic C to the SSA of the fractionated materials. On average, organic matter was calculated to contribute 49% of the CEC and 19% of the SSA of the fractionated materials. Because "independent" variables were themselves highly correlated, principal components regression analysis was used to improve the precision of estimates of organic matter contributions derived from the partial regression coefficients.
(C) Williams & Wilkins 1989. All Rights Reserved.
The Broadbalk Wheat Experiment at Rothamsted (UK) includes plots given the same annual applications of inorganic nitrogen (N) fertilizer each year since 1852 (48, 96 and 144 kg N/ha, termed N 1 N 2 and N 3 respectively). These very long-term N treatments have increased total soil N content, relative to the plot never receiving fertilizer N (N 0 ), due to the greater return of organic N to the soil in roots, root exudates, stubble, etc (the straw is not incorporated). The application of 144 kg N/ha for 135 years has increased total soil N content by 21%, or 570 kg/ha (0–23 cm). Other plots given smaller applications of N for the same time show smaller increases; these differences were established within 30 years. Increases in total soil N content have been detected after 20 years in the plot given 192 kg N/ha since 1968 (N 4 ).
There was a proportionally greater increase in N mineralization. Crop uptake of mineralized N was typically 12–30 kg N/ha greater from the N 3 and N 4 treatments than the uptake of c. 30 kg N/ha from the N 0 treatment. Results from laboratory incubations show the importance of recently added residues (roots, stubble, etc) on N mineralization. In short-term (2–3 week) incubations, with soil sampled at harvest, N mineralization was up to 60% greater from the N 3 treatment than from N 0 . In long-term incubations, or in soil without recently added residues, differences between long-term fertilizer treatments were much less marked. Inputs of organic N to the soil from weeds (principally Equisetum arvense L.) to the N 0 –N 2 plots over the last few years may have partially obscured any underlying differences in mineralization.
The long-term fertilizer treatments appeared to have had no effect on soil microbial biomass N or carbon (C) content, but have increased the specific mineralization rate of the biomass (defined as N mineralized per unit of biomass).
Greater N mineralization will also increase losses of N from the system, via leaching and gaseous emissions. In December 1988 the N 3 and N 4 plots contained respectively 14 and 23 kg/ha more inorganic N in the profile (0–100 cm) than the N 0 plot, due to greater N mineralization. These small differences are important as it only requires 23 kg N/ha to be leached from Broadbalk to increase the nitrate concentration of percolating water above the 1980 EC Drinking Water Quality Directive limit of 11·3mgN/l.
The use of fertilizer N has increased N mineralization due to the build-up of soil organic N. In addition, much of the organic N in Broadbalk topsoil is now derived from fertilizer N. A computer model of N mineralization on Broadbalk estimated that after applying 144 kg N/ha for 140 years, up to half of the N mineralized each year was originally derived from fertilizer N.
In the short-term, the amount of fertilizer N applied usually has little direct effect on losses of N over winter. In most years little fertilizer-derived N remains in Broadbalk soil in inorganic form at harvest from applications of up to 192 kg N/ha. However, in two very dry years (1989 and 1990) large inorganic N residues remained at harvest where 144 and 192 kg N/ha had been applied, even though the crop continued to respond to fertilizer N, up to at least 240 kg N/ha.
Two methods have been used previously to resolve the ‘mineral’ and ‘organic’ fractions of the cation exchange capacities of soils. Williams (1932) and Hallsworth & Wilkinson (1958) used multiple regression analysis to relate cation exchange capacity (CEC) in several soils to percentage organic matter (OM) and percentage clay, and thence to calculate the average values of the CECs of OM and clay. For individual soils, Davies & Davies (1965) and Clark & Nichol (1968) measured the CEC before and after oxidizing the OM with hydrogen peroxide.(Received March 12 1970)
Samples from field plots of silty soils in East Anglia, which were high and low in organic matter, were subjected to mild ultrasonic vibration. In soils high in organic matter particles in the 2–20 μm or 20–50 μMm size range contained most humified organic matter, whereas in soils low in organic matter, most was present in the clay sized fraction. Scanning electron micrographs of the ultrasonically separated particles showed that those from the high organic matter soils had more extensive surface coatings. Clean fragments were left after peroxide and calgon dispersion treatment.
Die Beeinflussung der Kohäsion und des Reibungswinkels durch organische Substanz wurde an Mischungen aus Feinsand und 0‐8 Gew. % Hochmoortorf mit verschiedenen Humifizierungsgraden bei unterschiedlichen Wasserspannungen untersucht. Die Differenzierung unterschiedlicher Humifizierungsgrade erfolgte mit einer Thermowaage.
Die Ergebnisse zeigen, daä die Kohäsion und der Winkel der inneren Reibung mit steigendem Gehalt an organischer Substanz zunehmen und jeweils größere Werte für das geringer zersetzte Material auftreten. Besonders unterhalb von 5 Gew. % organischer Substanz sind die Ergebnisse für die Kohäsion und den Winkel der inneren Reibung wasserspannungsabhängig und zeigen im Bereich um 50 hPa ein Maximum.
Als Erklärungsansatz fßr den Einfluß des Humifizierungsgrades auf die Stabilität wurde mit einem einfachen Modell die Kohäsion durch Wassermenisken in Abhängigkeit von Partikelgröße und Benetzbarkeit der organischen Substanz berechnet. Eine mögliche Ursache für die geringere Kohäsion bei hohem Humifizierungsgrad wird in der geringeren Benetzbarkeit vermutet. Analoge Vorstellungen für die Veränderung des Reibungswinkels in Abhängigkeit von der Wasserspannung müssen noch weiter entwickelt werden.