Cropland Management Practices Research Articles

Long-term straw return increases fungal residual contribution to soil microaggregate nitrogen pool: An eco-enzymatic stoichiometric study

Straw return is a widespread agricultural practice for improving cropland nitrogen (N) stocks. However, the contribution of microbial N to the soil aggregate N pool and the underlying microbial metabolic regulation mechanisms remain uncertain. This study was based on a 13-year field experiment with rice (Oryza sativa L.) and wheat (Triticum aestivum L.) rotation, using only a chemical fertilizer alone (CF) as the control. We analyzed the effects of the chemical fertilizer combined with (CS, 9500 kg ha−1 y−1) and wheat (4000 kg ha−1 y−1) straw on microbial derived-N, microbial carbon (C) and N limitations. We also assessed microbial N use efficiency (NUE) in various aggregates of ferric lixisols (0–20 cm). Rotary tillage reached a depth of 20 cm. The CS significantly increased microbial-derived N concentrations in soil aggregates and enhanced the contribution of fungal residual N to the N pool in aggregates < 0.25 mm, but did not affect those > 0.25 mm. Conversely, the bacterial contribution to the N pool was not affected by CS. Meanwhile, CS significantly increased the soil organic C and microbial biomass in the aggregates. The results of our eco-enzymatic stoichiometric model revealed that the CS significantly alleviated microbial C limitations and increased microbial NUE in soil aggregates. Structural equation modeling further revealed that the microbial biomass and soil organic C contents are key drivers of the microbial C limitation. The increased contribution of fungal residual N to the N pools in < aggregates 0.25 mm was attributed to improved microbial NUE resulting from the straw, without altering net N mineralization rates or β-1,4-N-acetylglucosidase activity. Our findings suggest that straw return promotes microbial-derived N production and sequestration by alleviating microbial C limitation. The strategies governing these microbial-derived N responses in aggregates to straw return might vary. This might be valuable for designing cropland management practices to improve N storage.

Incorporating agricultural practices in digital mapping improves prediction of cropland soil organic carbon content: The case of the Tuojiang River Basin

Accurate mapping of soil organic carbon (SOC) in cropland is essential for improving soil management in agriculture and assessing the potential of different strategies aiming at climate change mitigation. Cropland management practices have large impacts on agricultural soils, but have rarely been considered in previous SOC mapping work. In this study, cropland management practices including carbon input (CI), length of cultivation (LC), and irrigation (Irri) were incorporated as agricultural management covariates and integrated with natural variables to predict the spatial distribution of SOC using the Extreme Gradient Boosting (XGBoost) model. Additionally, we evaluated the performance of incorporating agricultural management practice variables in the prediction of cropland topsoil SOC. A case study was carried out in a traditional agricultural area in the Tuojiang River Basin, China. We found that CI was the most important environmental covariate for predicting cropland SOC. Adding cropland management practices to natural variables improved prediction accuracy, with the coefficient of determination (R2), the root mean squared error (RMSE) and Lin's Concordance Correlation Coefficient (LCCC) improving by 16.67%, 17.75% and 5.62%, respectively. Our results highlight the effectiveness of incorporating agricultural management practice information into SOC prediction models. We conclude that the construction of spatio-temporal database of agricultural management practices derived from inventories is a research priority to improve the reliability of SOC model prediction.

A framework to estimate climate mitigation potential for US cropland using publicly available data

The US agricultural sector is proposed as one opportunity to contribute to greenhouse gas (GHG) emissions reductions—reductions that are needed to limit atmospheric warming to be more in line with the US Nationally Determined Contribution to the Paris Agreement. Improved management of agricultural soils can both mitigate GHG emissions and increase carbon (C) sequestration, but disagreement exists regarding what levels of adoption are possible and to what extent they may mitigate net GHG emissions. In this paper, we provide a framework for setting reasonable, short-term conservation practice adoption targets and quantifying the associated net emissions reductions. Our framework was constructed using USDA-based publicly available inventory data and mitigation potentials from the COMET-Planner tool scaled to nine farm resource regions. The framework includes 2017 levels of conservation practice adoption and two 10-year growth scenarios: business-as-usual (BAU) and accelerated adoption rates. We evaluated six cropland management practices and practices associated with Conservation Reserve Program (CRP) establishment. Based on existing (2017) census data, we estimated that 134.2 million tonnes (Mt) carbon dioxide equivalents (CO₂e) per year have been or continue to be reduced through the adoption of conservation management practices on a cumulative total of 133.5 million hectares (Mha) of cropland. Under the BAU scenario, we estimated an additional 6.2 Mha y⁻¹ of adoption could result in a reduction potential of 48.7 Mt CO₂e y⁻¹. Under the accelerated scenario, we estimated an additional 13.1 Mha y⁻¹ of adoption could result in a reduction potential of 118.5 Mt of CO₂e y⁻¹ over the next 10 years. This framework highlights three key outcomes: (1) agriculture has had a substantial impact on GHG mitigation through existing/historical adoption of six cropland management practices and conversion of lands to the CRP; (2) these shifts in adoption provide an important baseline to make future projections of changes in practice adoption given regional trends and the resulting GHG mitigation potentials; and (3) disaggregating national estimates to the farm resource region level can help to inform and prioritize programs and policies consistent with existing climate goals. Estimates reported here reflect the current state of national modeling efforts and agricultural inventory sources. As new data such as the pending 2022 Ag Census report and model enhancements are made, the framework we outline here can be used to revise and update the estimates to improve accuracy and applicability.

Effects of land clearing for agriculture on soil organic carbon stocks in drylands: A meta-analysis.

Agricultural activities have been expanding globally with the pressure to provide food security to the earth's growing population. These agricultural activities have profoundly impacted soil organic carbon (SOC) stocks in global drylands. However, the effects of clearing natural ecosystems for cropland (CNEC) on SOC are uncertain. To improve our understanding of carbon emissions and sequestration under different land uses, it is necessary to characterize the response patterns of SOC stocks to different types of CNEC. We conducted a meta-analysis with mixed-effect model based on 873 paired observations of SOC in croplands and adjacent natural ecosystems from 159 individual studies in global drylands. Our results indicate that CNEC significantly (p < .05) affects SOC stocks, resulting from a combination of natural land clearing, cropland management practices (fertilizer application, crop species, cultivation duration) and the significant negative effects of initial SOC stocks. Increases in SOC stocks (in 1m depth) were found in croplands which previously natural land (deserts and shrublands) had low SOC stocks, and the increases were 278.86% (95% confidence interval, 196.43%-361.29%) and 45.38% (26.53%-62.23%), respectively. In contrast, SOC stocks (in 1m depth) decreased by 24.11% (18.38%-29.85%) and 10.70% (1.80%-19.59%) in clearing forests and grasslands for cropland, respectively. We also established the general response curves of SOC stocks change to increasing cultivation duration, which is crucial for accurately estimating regional carbon dynamics following CNEC. SOC stocks increased significantly (p < .05) with high long-term fertilizer consumption in cleared grasslands with low initial SOC stocks (about 27.2Mg ha-1 ). The results derived from our meta-analysis could be used for refining the estimation of dryland carbon dynamics and developing SOC sequestration strategies to achieve the removal of CO2 from the atmosphere.

Spatiotemporal changes in cropland soil organic carbon in a rapidly urbanizing area of southeastern China from 1980 to 2015

AbstractUnderstanding the spatiotemporal changes in soil organic carbon (SOC) and their driving factors is an important prerequisite in decision‐making for maintaining sustainable agricultural development and addressing climate change. However, the impacts of urbanization‐induced changes in cropland management practices on the spatiotemporal changes in SOC and their implications remain unclear, in particular over different time periods. In this study, a total of 1219 cropland topsoil SOC data (0–20 cm) were collected from a rapidly urbanizing area of southeastern China (southern Jiangsu Province) in 1980, 2000, and 2015, and geostatistical sequential Gaussian simulations were used to identify the changes in the spatiotemporal patterns of SOC during the period of 1980–2015. Results showed that the changes in SOC within the different time periods were significantly different, with a net increment of 3.65 g kg−1during the period of 1980–2000 and a net decrement of 2.32 g kg−1during the period of 2000–2015. Significant SOC accumulation occurred throughout the study area during 1980–2000, while SOC decline became predominant in the southeast during 2000–2015. Overall, the SOC contents for 60% of the study area increased significantly over the entire 35‐year period. The SOC increase during the first two decades (1980–2000) was largely attributed to the increasing soil C input that resulted from the enhanced crop productivity by chemical fertilizers, while the stagnant soil carbon inputs associated with the rapid urban expansion were the primary reason for constraining cropland SOC accumulation in the subsequent 15 years (2000–2015). These findings highlight the importance of balancing agricultural development and urbanization processes to maintain SOC levels, and may also provide some guidance for planning cropland soil C management strategies in many areas that are undergoing similar urbanization processes.

Off-Season Agriculture Encroachment in the Uplands of Northern Pakistan: Need for Sustainable Land Management

Agriculture encroachment over alpine pastoral land is posing serious threats to the sustainable use of natural resources and agro-pastoral systems in the upland environment. This study aimed to understand the scenario of agriculture encroachment within a sustainable land management context in Northern Pakistan’s uplands (Buhrawai). Both quantitative and qualitative methodological approaches were used for the primary data collection on the pattern of cropland expansion, cropland productivity, agrochemical inputs, and perceived socio-ecological system. The results showed that off-season agriculture has emerged as a cash-earning livelihood activity, largely adopted by decade-old and influential tenant communities in the study areas. During the last few decades, this off-season agriculture regularly expanded from lower- to higher-elevation (2980–3800 m) areas, and extensively encroached on accessible pastoral areas in the bottomlands. Cultivation of the two major vegetable crops, i.e., peas and potatoes, occurred on a total of 417.4 ha of pastoral land, where pea cultivation predominantly occurred on 367.2 ha and potato cultivation on 50.2 ha of pastoral land. We found that repeated cultivation of the same crops, without crop rotation and land management practices, significantly reduced land productivity with time; the crop productivity was recorded to be the highest in the virgin cultivated land (pea: 1.8 tons/ha and potato: 14.8 tons/ha) and the lowest in the old-cultivated land (pea: 0.6 tons/ha and potato: 8.2 tons/ha). As a result of this trend, farmers are abandoning unproductive agricultural land and subsequently starting cultivation in other marginal areas, even cultivating crops on steeper slopes beyond the permissible level (16°). These findings revealed that farmers have extensively used key pastoral areas for cultivation, and they have deprived landless pastoralists of their traditional grazing land in the uplands. Furthermore, this agriculture encroachment imposed serious pressure on the pastoralists’ livelihoods and the upland ecosystem on which they rely. Therefore, policies and regulations that promote sustainable land management are much needed to ensure socio-economic equity and ecological integrity in the uplands of Northern Pakistan.

Can cropland management practices lower net greenhouse emissions without compromising yield?

Smart cropland management practices can mitigate greenhouse gas (GHG) emissions while safeguarding food security. However, the integrated effects on net greenhouse gas budget (NGHGB) and grain yield from different management practices remain poorly defined and vary with environmental and application conditions. Here, we conducted a global meta-analysis on 347 observation sets of non-CO2 GHG (CH4 and N2 O) emissions and grain yield, and 412 observations of soil organic carbon sequestration rate (SOCSR). Our results show that for paddy rice, replacing synthetic nitrogen at the rate of 30%-59% with organic fertilizer significantly decreased net GHG emissions (NGHGB: -15.3±3.4 [standard error], SOCSR: -15.8±3.8, non-CO2 GHGs: 0.6±0.1 in Mg CO2 eq ha-1 year-1 ) and improved rice yield (0.4±0.1 in Mg ha-1 year-1 ). In contrast, intermittent irrigation significantly increased net GHG emissions by 11.2±3.1 and decreased rice yield by 0.4±0.1. The reduction in SOC sequestration by intermittent irrigation (15.5±3.3), which was most severe (>20) in alkaline soils (pH>7.5), completely offset the mitigation in CH4 emissions. Straw return for paddy rice also led to a net increase in GHG emissions (NGHGB: 4.8±1.4) in silt-loam soils, where CH4 emissions (6.3±1.3) were greatly stimulated. For upland cropping systems, mostly by enhancing SOC sequestration, straw return (NGHGB: -3.4±0.8, yield: -0.5±0.6) and no-tillage (NGHGB: -2.9±0.7, yield: -0.1±0.3) were more effective in warm climates. This study highlights the importance of carefully managing croplands to sequester SOC without sacrifice in yield while limiting CH4 emissions from rice paddies.

Aboveground litter inputs determine carbon storage across soil profiles: a meta-analysis

AimsAboveground plant litter inputs are important sources of soil carbon (C). We aimed to establish how experimentally altered litter inputs affect soil C to 1-m depth across different ecosystems, and over different timeframes.MethodsWe performed a meta-analysis of 237 studies across 248 sites worldwide to assess the influence of treatment magnitude, treatment duration, initial soil C content, and climate on the response of soil C to altered aboveground litter inputs.ResultsOverall, soil C content was lower under litter removal, but higher under litter addition compared to controls. The effects of litter manipulation were apparent throughout the soil profile and were related to treatment magnitude. Soil C content declined markedly with increasing duration of litter removal, whereas the positive effect of litter addition attenuated over time. Cropland management practices (bare fallow or additional straw incorporation) had similar effects on soil C to litter removal and addition treatments.ConclusionsOur study reveals rapid and consistent changes in soil C content with altered litter inputs and provides important insights into plant residue management to enhance soil C sequestration. We highlight the need for long-term experiments, with a greater focus on the processes underpinning soil C storage in different ecosystems.

Evaluation of Slug Refuge Traps in a Soybean Reduced-Tillage Cover Crop System.

Simple SummarySlugs have become more frequent pests of field crops, including soybean. Monitoring slugs during the day is difficult because slugs are nocturnal, so trapping is often used to monitor populations. A variety of traps have been developed, though there are few direct comparisons of the different trap types. The objective of this study was to compare trapping efficiency of two types of slug refuge traps in soybeans. We tested a traditional shingle trap and a modified shingle trap with a water-filled pitfall trap beneath it. The modified shingle traps captured significantly more slugs than the traditional shingle trap, mainly due to the pitfall component (which was significantly cooler than the shingle component). As slug density decreased, this trend was most pronounced, suggesting that the modified shingle trap is a more sensitive sampling tool which may be useful in agronomic slug research.As more farmers adopt no- or reduced-tillage and/or cover crop land management practices, slugs have become more frequent pests of field crops, including soybean. Monitoring slugs visually is difficult because they are nocturnal, so several trapping methods have been developed, though comparisons of trap types are rare. The objective of this study was to compare trapping efficiency of two types of slug refuge traps in reduced-tillage soybeans following cover crop termination. We tested a traditional shingle trap and a modified shingle trap with a water-filled pitfall trap beneath it. Traps were deployed in 24 pairs in 2018 and 2019 in experimental soybean plots. We counted slug captures weekly over a 5-week time period each year. In 2018, we counted the total number of slugs under each trap type. In 2019, counts were categorized into specific trap components (shingle vs. in/on/under the pitfall). Temperature was also recorded in 2019. The modified shingle traps captured significantly more slugs than the traditional shingle traps, mainly due to the pitfall component. This trend was most pronounced as slug density decreased, suggesting that the modified shingle trap is a more sensitive sampling tool which may be particularly valuable when used for research purposes.

Linking ecosystem services trade-offs, bundles and hotspot identification with cropland management in the coastal Hangzhou Bay area of China

Understanding the co-occurrence of multiple ecosystem services within farming systems and how they are associated across space are relatively new topics. Quantifying ecosystem services and their interactions as dependent on cropland management can help to formulate a more effective and sustainable land use management system. However, current academic efforts and cropland management practices based on the perspective of ecosystem services bundles and tradeoffs remain limited, especially in developing countries. This paper aimed to integrate ecosystem services into cropland protection and functional zoning. Taking Cixi County in the Hangzhou Bay area, China, as the case study area, five typical ecosystem services (food supply, carbon sequestration, hydrological regulation, soil fertility and recreation potential) delivered by croplands and their correlations were quantitatively assessed. The results demonstrated a heterogeneous spatial pattern of multiple ecosystem services and diverse interactions between them, which depended on regional specific conditions and agricultural activities. Further, we adopted the framework of ecosystem services bundles as a planning tool to support the spatial strategy of cropland management. Cropland protection priority and functional zoning were determined by hotspot analysis and clustering algorithms, respectively. The croplands in Cixi were classified into three protection grades and a zoning scheme comprising four functional types with policy guidelines was proposed based on the spatial cluster results. The integrative approach used in this study is applicable to supplement the current cropland management actions by incorporating the perspective of ecosystem services tradeoff and bundles.

Scaling Up Agricultural Research With Artificial Intelligence

Agricultural systems are enormously variable in space and time. New and developing artificial intelligence (AI)-based tools can leverage site-based science and big data to help farmers and land managers make site-specific decisions. These tools are improving information about soils and vegetation that forms the basis for investments in management actions, provides early warning of pest and disease outbreaks, and facilitates the selection of sustainable cropland management practices. Continued progress with AI will require more observational data across a wide range of agricultural settings, over long time periods.

Determinants of Crop Land Management Practices: The Case of North Gondar Zone, North West Ethiopia

Land management problems like soil erosion; overgrazing and deforestation have steadily increased in Ethiopia including the study area North Gondar Zone. Thus, the main objective of this study is to assess the determinants of crop land management practices in north Gondar zone. Both qualitative and quantitative types of data were collected from primary and secondary sources. In this study, to get representative sample from different agro ecologies a stratified simple random sampling technique was employed to select sample household heads. Finally, a total of 120 household heads were drawn through simple random sampling technique proportionally to size form the sample kebeles. To analyze the determinants of land management practices multinomial logit model was used. The findings of this study indicated that from the total variables included in the model only six variables are found to significantly affect the choice of crop land management strategies. The significant variables include age of the household head, education level, access to mass media, amount of income, farm distance and the frequency of extension contact. Thus, any concerned bodies should strengthen rural households’ mass media coverage and advisory services.

Managing cropland and rangeland for climate mitigation: an expert elicitation on soil carbon in California

Understanding the magnitude of and uncertainty around soil carbon flux (SCF) is important in light of California’s efforts to increase SCF (from the atmosphere to soils) for climate change mitigation. SCF depends, to a great extent, on how soils are managed. Here, we summarize the results of an elicitation of soil science and carbon cycle experts aiming to characterize understanding of current SCF in California’s cropland and rangeland, and how it may respond to alternative management practices over time. We considered four cropland management practices—biochar, compost, cover crops, and no-till—and two rangeland management practices, compost and high-impact grazing. Results across all management practices reveal underlying uncertainties as well as very modest opportunities for soil carbon management to contribute meaningfully to California’s climate mitigation. Under median scenarios, experts expect all the surveyed management practices to reverse SCF from negative to positive, with direct carbon additions via biochar and compost offering the best potential for boosting the soil carbon pool.

Soil carbon management in large-scale Earth system modelling: implications for crop yields and nitrogen leaching

Abstract. Croplands are vital ecosystems for human well-being and provide important ecosystem services such as crop yields, retention of nitrogen and carbon storage. On large (regional to global)-scale levels, assessment of how these different services will vary in space and time, especially in response to cropland management, are scarce. We explore cropland management alternatives and the effect these can have on future C and N pools and fluxes using the land-use-enabled dynamic vegetation model LPJ-GUESS (Lund–Potsdam–Jena General Ecosystem Simulator). Simulated crop production, cropland carbon storage, carbon sequestration and nitrogen leaching from croplands are evaluated and discussed. Compared to the version of LPJ-GUESS that does not include land-use dynamics, estimates of soil carbon stocks and nitrogen leaching from terrestrial to aquatic ecosystems were improved. Our model experiments allow us to investigate trade-offs between these ecosystem services that can be provided from agricultural fields. These trade-offs are evaluated for current land use and climate and further explored for future conditions within the two future climate change scenarios, RCP (Representative Concentration Pathway) 2.6 and 8.5. Our results show that the potential for carbon sequestration due to typical cropland management practices such as no-till management and cover crops proposed in previous studies is not realised, globally or over larger climatic regions. Our results highlight important considerations to be made when modelling C–N interactions in agricultural ecosystems under future environmental change and the effects these have on terrestrial biogeochemical cycles.

Terrestrial net primary productivity in India during 1901–2010: contributions from multiple environmental changes

India is very important but relatively unexplored region in terms of carbon studies, where significant environmental changes have occurred in the 20th century that can alter terrestrial net primary productivity (NPP). Here, we used a process-based, Dynamic Land Ecosystem Model (DLEM), driven by land cover and land use change (LCLUC), climate change, elevated atmospheric CO2 concentration, atmospheric nitrogen deposition (NDEP), and tropospheric ozone (O3) pollution to estimate terrestrial NPP in India during 1901–2010. Over the country, terrestrial NPP showed significant inter-annual variations ranging 1.2 Pg C year−1 to 1.7 Pg C year−1 during the 1901–2010. Overall, multiple environmental changes have increased terrestrial NPP by 0.23 Pg C year−1. Elevated atmospheric CO2 concentration has increased NPP by 0.29 Pg C; however climate change has offset a portion of terrestrial NPP (0.11 Pg C) during this study period. On an average, terrestrial NPP reduced by 0.12 Pg C year−1 in drought years; when precipitation was 100 mm year−1 lower than long term average, suggesting that terrestrial carbon cycle in India is strongly linked to climate change. LCLUC, including land conversions and cropland management practices, increased terrestrial NPP by 0.043 Pg C year−1 over the country. Tropospheric O3 pollution reduced terrestrial NPP by 0.06 Pg C year−1 and the decrease was comparatively higher in croplands than other biomes after the 1980s. Our results have shown that climate change and tropospheric O3 pollution may partially offset terrestrial NPP increase caused by elevated CO2 concentration, LCLUC, and NDEP over India.

In stable, unmanaged grasslands local factors are more important than landscape-level factors in shaping spider assemblages

Previous studies reported that landscape-level factors are vital to support diversity of spiders in strongly modified arable lands and disturbed habitats such as managed semi-natural grasslands. Cropland management (ploughing, fertilization, and pest management) and agricultural practices (mowing and grazing) destroy and/or modify regularly the spider assemblages; thus, continuous recolonization from the surrounding landscape is vital to sustain the species pool. On the contrary, we hypothesized that in unmanaged grasslands, the spider assemblages are stable and the importance of recolonization is limited, the local factors become much more important drivers in shaping spider assemblages than landscape-level factors. We tested the importance of local and landscape-level factors on the abundance and species richness of spiders in unmanaged grasslands. At the landscape-level, we found that only the isolation had significant effect on the total abundance, on the abundance of hunting and habitat specialist species, and on the abundance of a frequent species (Gnaphosa mongolica). At the local scale, however, four out of five studied factors influenced significantly the species richness and abundance of spider assemblages and the abundance of two frequent species (Alopecosa psammophila, Berlandia cinerea). Species richness and abundance increased by plant cover, litter cover, and patch size, while decreased by bare ground cover. We found that in unmanaged grasslands, the local factors had vital role in maintaining the spider species richness; this is just the opposite conclusion that was earlier reported for agricultural ecosystems, where landscape-level effects had crucial role providing the species for continuous recolonization.

Magnitude, Spatiotemporal Patterns, and Controls for Soil Organic Carbon Stocks in India during 1901–2010

To the best of our knowledge, no attempts have been made to understand how environmental changes that occurred in the 20th century have altered soil organic carbon (SOC) dynamics in India. In this study, we applied a process‐based Dynamic Land Ecosystem Model (DLEM), to estimate the magnitude as well as to quantify the effects of climate change and variability, land cover and land‐use change (LCLUC), carbon dioxide (CO2) concentration, atmospheric nitrogen deposition (NDEP), and tropospheric ozone (O3) pollution on SOC stocks in India during 1901–2010. The DLEM simulations have shown that SOC stocks ranged from 20.5 to 23.4 Pg C (1 Pg = 1015 g), majority of which is stored in the forested areas in the north‐east, north, and few scattered regions in the southern India. During the study period, soils have sequestered SOC by 2.9 Pg C. Elevated CO2 concentration has increased total SOC stocks over the country by 1.28 Pg C, which was partially offset by climate change (0.78 Pg C) and tropospheric O3 pollution (0.20 Pg C) during 1901–2010. Interestingly, LCLUC increased SOC stocks by 1.7 Pg C thereby suggesting that SOC loss from deforestation was offset by the conversion of low productive fallow lands and other lands to croplands that received irrigation along with N fertilizers. Atmospheric nitrogen deposition (NDEP) has increased biomass production and SOC by 0.5 PgC over the country. This study has demonstrated that the benefits from elevated CO2 concentration, cropland management practices, and NDEP in sequestering SOC stocks were offset by climate change and tropospheric O3 pollution which should be curbed in India.

Effects of drainage ditches and stone bunds on topographical thresholds for gully head development in North Ethiopia

Gully erosion is an extreme process of land degradation operating in different regions of the world. A common way to quantify the susceptibility of land to gully incision is the use of topographical thresholds for different land use types. However, the impact of various management practices in cropland on these thresholds has not been studied to date, although land management may significantly affect runoff production, erosion processes and rates. Here, the impact of different land management practices on gully head development in cropland is studied based on a standardized procedure for topographical threshold analysis: s>kA−b, where s represents the slope gradient of the soil surface, A the drainage area at the gully head, b an exponent and k a coefficient reflecting the resistance of the land to gully head development. A case study area was chosen around Wanzaye, North Ethiopia, where three different cropland management practices were studied in 75 catchments: (i) the catchment-wide use of stone bunds on the contour, (ii) the use of slightly sloping drainage ditches (feses), and (iii) the combined use of stone bunds and feses. The lowest k-values (0.078–0.090) are found for catchments treated with feses, the highest k-values (0.198–0.205) are observed for stone bund catchments, and medium k-values (0.092–0.099) are found for mixed catchments. This finding implies that catchments with the exclusive use of drainage ditches are the most vulnerable to gully head development compared with mixed catchments and stone bund catchments. However, on-site sheet and rill erosion rates are reduced by feses as they lower the gradient of the overland flow lines. Three trends in cropland management around Wanzaye and the wider region are observed: (i) feses are exclusively made on rather steep slopes where small drainage areas lead to the rapid development of gully heads; (ii) stone bunds are constructed on both steeper and gentle sloping cropland; and (iii) larger and gently sloping catchments seem to be most suitable for the combined use of drainage ditches and stone bunds.

Quantifying the contributions of agricultural oasis expansion, management practices and climate change to net primary production and evapotranspiration in croplands in arid northwest China

Cropland area in north-western China has quadrupled over the past 50 years. The effects of this rapid expansion on regional carbon and water budgets have not been examined quantitatively. In this study, an enhanced Biome-BGC model including crop growth processes was used to quantify the effects on regional net primary productivity (NPP) and evapotranspiration (ET) in a representative catchment. The model results were in good agreement with biometric measurements. The catchment-scale total NPP (TNPP) and total ET (TET) increased by 81.8% and 89.4%, respectively. The increase in cropland area (LUCC) explained 40.3% and 60.5% of the increased TNPP and TET, while management practices (Mana) accounted for 46.1% and 16.8% of the increased TNPP and TET, respectively. Climate change (CLM) had the least influence on the increase in TNPP and TET (accounting for 1.8% and 4.7%). As assuming no interactions between CLM and LUCC, we detected effects of interactions between CLM and Mana (accounting for 10% and 16.8%) and between Mana and LUCC (accounting for 1.8% and 4.7%) on the increased TNPP and TET. These results implied that the rapid expansion of cropland and intensive agricultural management practices had important effects on regional carbon and water budgets.

Potential of global cropland phytolith carbon sink from optimization of cropping system and fertilization.

The occlusion of carbon (C) by phytoliths, the recalcitrant silicified structures deposited within plant tissues, is an important persistent C sink mechanism for croplands and other grass-dominated ecosystems. By constructing a silica content-phytolith content transfer function and calculating the magnitude of phytolith C sink in global croplands with relevant crop production data, this study investigated the present and potential of phytolith C sinks in global croplands and its contribution to the cropland C balance to understand the cropland C cycle and enhance long-term C sequestration in croplands. Our results indicate that the phytolith sink annually sequesters 26.35±10.22 Tg of carbon dioxide (CO2) and may contribute 40±18% of the global net cropland soil C sink for 1961–2100. Rice (25%), wheat (19%) and maize (23%) are the dominant contributing crop species to this phytolith C sink. Continentally, the main contributors are Asia (49%), North America (17%) and Europe (16%). The sink has tripled since 1961, mainly due to fertilizer application and irrigation. Cropland phytolith C sinks may be further enhanced by adopting cropland management practices such as optimization of cropping system and fertilization.