Higher Soil Organic Carbon Research Articles

Major contributions of agricultural management practices to topsoil organic carbon distribution and accumulation in croplands of East China over three decades

Multiple natural and anthropogenic factors jointly drive the spatial distribution of soil organic carbon (SOC) and its dynamics in croplands. Among these factors, agricultural management practices have caused considerable impacts. Previous studies on the driving factors of SOC in croplands have provided significant understanding on this matter. However, whether and how the effects and interplay of these drivers change over time is often unknown, especially agricultural activities. To measure the effects of agricultural management practices on the spatial distribution and temporal change of SOC incorporating the network relationships with other natural drivers at the regional scale, we conducted partial least squares path analysis on the topsoil organic carbon content using two historical soil datasets from cropland samples in East China obtained during the 1980s and the 2010s. Eight indicators and their temporal changes reflecting climate, agricultural management, and edaphic conditions were used to quantify the driving mechanisms of the spatial distribution and temporal change of SOC. The drivers of SOC distribution showed that high SOC was mostly distributed in soils with a relatively low pH and high clay content in warm humid climates. High SOC was associated with the application of N fertilizer, crop residue input, and agricultural machinery in the 1980s and 2010s. The effect of N fertilization on SOC distribution increased from the 1980s to the 2010s, whereas the total edaphic effects significantly decreased from 0.62 to 0.25 (P < 0.01). Regarding the drivers of SOC change over the three decades, the edaphic effects presented the strongest effect (path coefficient of 0.74, P < 0.01), including the negative effects of topsoil acidity and baseline SOC level, as well as the positive effects of total nitrogen (TN) and clay content change. Croplands with lower intensity of management practices in the 1980s generally attained more development in agricultural modernization, which led to a considerable SOC increase. Our research revealed the importance of agricultural management practices on the spatial distribution and temporal change of cropland SOC at the regional scale. The results emphasize the need to measure the changing driving mechanisms of SOC dynamics. The findings indicate that indicators reflecting the effects of agricultural management practices should be included in digital mapping and process-based modeling of soil carbon at different spatiotemporal scales to improve prediction accuracy.

Soil organic carbon is buffered by grass inputs regardless of woody cover or fire frequency in an African savanna

Abstract Woody plant encroachment (WPE) is a global trend that occurs in many biomes, including savannas, and accelerates with fire suppression. Since WPE can result in increased storage of soil organic carbon (SOC), fire management, which may include fire suppression, can improve ecosystem carbon (C) sequestration in savannas. At our study site in Kruger National Park, South Africa, we used a long‐term (~70 year) fire experiment to study the drivers and consequences of changes in woody cover (trees and shrubs) on SOC sequestration. We surveyed four fire manipulation treatments, replicated at eight locations within the park: annual high‐intensity burns, triennial high (dry season) and low‐intensity (wet season) burns, and fire exclusion, to capture the range of fire management scenarios under consideration. The changes in woody cover were calculated over a period similar to the experiment's duration (~80 years) using aerial photographs (1944–2018). Soils were analysed to 30 cm depth for SOC and δ13C, under and away from the tree canopy to isolate local‐ and landscape‐level effects of WPE on SOC. The largest increases in woody cover occurred with fire exclusion. We found that plots with higher increases in woody cover also had higher SOC. However, trees were not the only contributor to SOC gains, sustained high inputs of C4‐derived C (grasses), even under canopies in fire suppression plots, contributed significantly to SOC. We observed little difference in SOC sequestration between cooler triennial (wet season) burns and fire suppression. Synthesis. Grass input to soil organic carbon (SOC) remained high across the full range of woody cover created by varying burning regimes. The total SOC stocks stored from tree input only matched grass‐derived SOC stocks after almost 70 years of fire exclusion. Our results point to C4 grasses as a resilient contributor to SOC under altered fire regimes and further challenge the assumption that increasing tree cover, either through afforestation schemes or fire suppression, will result in large gains in C sequestration in savanna soils, even after 70 years.

Conservation agriculture impacts on soil carbon sequestration under a cotton (Gossypium hirsutum)-wheat (Triticum aestivum) system in the Indo-Gangetic plains

Despite many studies reporting conservation agriculture (CA) impacts on soil organic carbon (SOC) sequestration, the impacts of long-term permanent bed planting under CA on SOC sequestration are rarely reported. Hence, this study assessed the permanent bed planted CA impacts on SOC sequestration rates in 0–30 and 30–60 cm soil depths under a cotton (Gossypium hirsutum L.)-wheat (Triticum aestivum L.) system in the Indo-Gangetic Plains (IGP). The treatments comprised diverse combinations of tillage and residue retention (R), viz. conventional tillage (CT), narrow bed, narrow bed + R, broad bed, broad bed + R, flat bed + R and flat bed. Results indicated that the total SOC stock was ~32, 31 and 29% higher in CA plots than in CT plots (farmers' practice), in 0–30 cm soil depth. The SOC sequestration rate (over CT plots) in the CA plots was ~0.76 Mg C/ha/yr. The broad bed + R, narrow bed + R and flat bed + R plots had appreciably high total SOC sequestration (~0.24 Mg C/ha/yr) compared to CT plots in deep soil layer (30–60 cm). The yield data (2-year mean basis) was recorded highest in the broad bed + R (3.48 tonnes/ha and 8.11 tonnes/ha for cotton and wheat, respectively) and flat bed + R (3.38 tonnes/ha and 8.46 tonnes/ha for cotton and wheat, respectively) treatments showing a positive impact of the adoption of long-term CA in the IGP. Thus, adopting raised beds with residue retention has great potential for higher carbon sequestration and improving yields and can be recommended for sustainable intensification of arable lands in the region.

Sustainable Cropping System Intensification in Arid Region of India: Fallow Replacement with Limited Duration Sorghum–Legume Intercropping Followed by Eruca sativa Mill. Grown on Conserved Soil Moisture

A field experiment was conducted to explore the possibilities of sustainable crop intensification in the fallow–Eruca sativa Mill. system in arid ecology by replacing fallow with short-duration sorghum–legume intercropping. The experiment was laid out in a split-plot design with two planting systems (bed and conventional) in main plots and a factorial combination of crop duration (50 and 60 days) and cropping systems (sole sorghum, sorghum + cowpea, sorghum + Sesbania in 2:2 ratio) in sub-plots. In the succeeding Eruca sativa crop, residuals and two gypsum levels (0 and 250 kg ha−1) were tested. Bed planting practiced during both seasons did not improve the system productivity to significant levels. Extending the duration of fallow replacement crops from 50 to 60 days significantly increased their forage yield, overall system productivity by 25–34%, and system net returns by 15.9–21.5%. Amongst the intercropping systems, the sorghum + Sesbania system added 10–13 tonnes ha−1Sesbania biomass to the soil, resulting in higher soil organic carbon, available nitrogen, dehydrogenase activity, and residual soil moisture, which increased the yield of the succeeding Eruca sativa crop by 8.8–15% compared to the residual of sole sorghum. However, it could not compensate for the yield loss due to the utilization of 50% of the area for growing the green manure crop. The sorghum + cowpea intercropping–Eruca sativa system was found to be the optimum combination with a system productivity of 1.27–1.87 Mg ha−1Eruca sativa seed equivalent. The productivity of Eruca sativa further improved by 9.5–23.7% due to the soil application of gypsum @ 250 kg ha−1. When averaged over treatments, fallow replacement during the rainy season reduced the available soil moisture at the sowing of Eruca sativa by 8.3–22.8% and subsequently its yield by 16.5–30.4% compared to the fallow–Eruca sativa system. However, with this production penalty, an additional rainy-season fodder crop was successfully grown, which improved the system productivity by 57.7–82.8%, net returns by 31.2–57.3%, and rainfall use efficiency from 0.21 to 36 USD/mm−1 ha−1. Hence, it may be concluded that short-duration fodder crops may be taken as fallow replacement crops for higher system productivity and rainfall use efficiency.

Patterns and abiotic drivers of soil organic carbon in perennial tea (Camellia sinensis L.) plantation system of China

Understanding soil organic carbon (SOC), the largest carbon (C) pool of a terrestrial ecosystem, is essential for mitigating climate change. Currently, the spatial patterns and drivers of SOC in the plantations of tea, a perennial leaf crop, remain unclear. Therefore, the present study surveyed SOC across the main tea-producing areas of China, which is the largest tea producer in the world. We analyzed the soil samples from tea plantations under different scenarios, such as provinces, regions [southwest China (SW), south China (SC), south Yangtze (SY), and north Yangtze (NY)], climatic zones (temperate, subtropical, and tropical), and cultivars [large-leaf (LL) and middle or small-leaf (ML) cultivars]. Preliminary analysis revealed that most tea-producing areas (45%) had SOC content ranging from 10 to 20 g kg−1. The highest SOC was recorded for Yunnan among the various provinces, the SW tea-producing area among the four regions, the tropical region among the different climatic zones, and the areas with LL cultivars compared to those with ML cultivars. Further Pearson correlation analysis demonstrated significant associations between SOC and soil variables and random forest modeling (RF) identified that total nitrogen (TN) and available aluminum [Ava(Al)] of soil explained the maximum differences in SOC. Besides, a large indirect effect of geography (latitude and altitude) on SOC was detected through partial least squares path modeling (PLS-PM) analysis. Thus, the study revealed a high spatial heterogeneity in SOC across the major tea-producing areas of China. The findings also serve as a basis for planning fertilization strategies and C sequestration policies for tea plantations.

Analysis of Soil Carbon Stock Dynamics by Machine Learning—Polish Case Study

A simplified differential equation for the dynamics of soil organic carbon (SOC) that describes the rate of SOC change (dSOC/dt) was constructed using the LASSO regression—a regularized linear regression machine learning method. This method selects the best predefined explanatory variables and empirically evaluates the relevant parameters of the equation. The result, converted into a formula for the long-term equilibrium level of soil carbon, indicates the existence of carbon sequestration potential in the studied regions of Poland. In particular, the model predicts high SOC content in regions with a high Topographic Wetness Index (TWI), such as river valleys or areas with high cattle density, as expected.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

Predicting soil organic carbon in cultivated land across geographical and spatial scales: Integrating Sentinel-2A and laboratory Vis-NIR spectra

Digital mapping of soil organic carbon (SOC) is essential for visualizing the spatial distribution at different regions and scales. However, existing studies using remote sensing are limited by the low spectral resolution of multispectral data for accurate estimation of SOC, and the failure of laboratory visible and near-infrared and shortwave infrared (Vis-NIR) spectroscopy to perform pixel-level mapping. To address these limitations, this study proposes a SOC mapping framework that integrates satellite earth observations and proximal sensing spectral data to reconstruct images having a spectral resolution of 400–2500 nm and a spatial resolution of 10 m, then the clustering probability analysis was applied on the reconstructed images, to develop a high accuracy SOC prediction model and demonstrate its effectiveness across geographical and spatial scales. Specifically, a total of 324 topsoil samples were collected from Baoqing and Suiling counties in northeast China, whose laboratory Vis-NIR reflectance spectra and SOC were measured. Sentinel-2A images of bare soils averaged over three years before and after the samples collection (i.e., 2018 to 2021) were collected. A total of 264 samples from eight fields in Belgium were used to evaluate the performance of the model at the field scale. Then, two models were developed (i) a global regression model with direct prediction using random forest and (ii) a clustering probability model with Gaussian Mixture Model-random forest. Results demonstrated that (1) reconstructed images produced more accurate prediction results than the individual laboratory Vis-NIR spectroscopy and Sentinel-2A models. (2) At the regional scale, clustering probability model achieved better performance in quantification of SOC (coefficient of determination [R2] = 0.78, and root mean square error [RMSE] = 0.78 %) than global regression model (R2 = 0.65, and RMSE = 1.06 %). (3) For field scale, the reconstructed image-based clustering probability SOC prediction model was shown to be effective when using the Belgium data, providing a R2 of 0.67, and RMSE of 0.15 %. (4) Integrating remote sensing multispectral and proximal Vis-NIR information can lead to a smoother and more continuous SOC distribution within the region, and can better show its spatial heterogeneity within the field. This study highlights the advantages of integrating remote sensing with proximal sensing for improving the accuracy of SOC prediction and mapping, enabling applicability of the model across geographical and spatial scales with appreciable accuracy.

Impact of land use/cover change and slope gradient on soil organic carbon stock in Anjeni watershed, Northwest Ethiopia.

Today's agri-food systems face the triple challenge of addressing food security, adapting to climate change, and reducing the climate footprint by reducing the emission of greenhouse gases (GHG). In agri-food systems, changes in land use and land cover (LULC) could affect soil physicochemical properties, particularly soil organic carbon (SOC) stock. However, the impact varies depending on the physical, social, and economic conditions of a given region or watershed. Given this, a study was conducted to quantify the impact of LULC and slope gradient on SOC stock and C sequestration rate in the Anjeni watershed, which is a highly populated and intensively cultivated area in Northwest Ethiopia. Seventy-two soil samples were collected from 0-15 and 15-30cm soil depths representing four land use types and three slope gradients. Soil samples were selected systematically to match the historical records (30years) for SOC stock comparison. Four land use types were quantified using Landsat imagery analysis. As expected, plantation forest had a significantly (p < 0.05) higher SOC (1.94Mgha-1) than cultivated land (1.38Mgha-1), and gentle slopes (1-15%) had the highest SOC (1.77Mgha-1) than steeper slopes (> 30%). However, higher SOC stock (72.03Mgha-1) and SOC sequestration rate (3.00Mgha-1year-1) were recorded when cultivated land was converted to grassland, while lower SOC stock (8.87Mgha-1) and sequestration rate (0.77Mgha-1year-1) were recorded when land use changed from cultivation to a plantation forest. The results indicated that LULC changes and slope gradient had a major impact on SOC stock and C sequestration rate over 30years in a highly populated watershed. It is concluded that in intensively used watersheds, a carefully planned land use that involves the conversion of cultivated land to grassland could lead to an increase in soil C sequestration and contributes to reducing the carbon footprint of agri-food systems.

Optimized bare soil compositing for soil organic carbon prediction of topsoil croplands in Bavaria using Landsat

Soil Organic Carbon (SOC) is amongst others an indicator for soil degradation and soil health of croplands. Induced by recent policy initiatives, awareness for high resolution SOC maps and techniques to estimate changes is increasing. For area-wide mapping approaches with at least a field resolution, Earth Observation is a valuable data source to extract bare soil areas and to quantify SOC contents for these areas. In this context, compositing techniques of multi-temporal image archives are widely used to overcome the limitation of vegetation cover of fields during the overpass of the satellite. Comparing current bare soil compositing approaches, two aspects are of particular importance: 1) the index for bare soil selection and 2) the length of the compositing period for recurrent analyses.In this study, we applied the Soil Composite Mapping Processor (SCMaP) to the full archive of Landsat data between 2005 and 2019 to optimize parameters for soil reflectance composite (SRC) generation of multitemporal satellite imagery for SOC predictions. For this purpose, three spectral indices (PV + BLUE, PV + IR2, and NBR2) for SRC generation were implemented in the SCMaP chain. For all three indices a validation of the extracted bare soil dates with field observations and phenological information from the crop calendar showed a reliable extraction of bare soil dates. Due to the crops in the investigation area, spring and autumn months indicated the highest proportion of correctly selected bare soil dates. We also analyzed the SOC modeling capabilities of different composed SRCs (indices and varying seasonal and temporal lengths) in combination with available legacy data. In comparison to a seasonal pre-selection of scenes (spring and autumn months) included in the SRC, the different indices showed a minor influence on SOC modeling. However, PV + BLUE performed best (R2: 0.56 – 0.72, RMSE: 1.09 – 1.29%, RPD: 1.51 – 1.91). Furthermore, we compared the SOC model capabilities for different SRC compositing lengths (3-, 5-, 7-, 10- and 15-years). For PV + BLUE and PV + IR2, longer compositing lengths (from three to 15 years) resulted in an increase of the model accuracies and performances. However, for NBR2 this was not as clear. Based on the results at least a 5-year compositing period is required for recurrent SOC predictions using Landsat data.

Small, Coastal Temperate Rainforest Watersheds Dominate Dissolved Organic Carbon Transport to the Northeast Pacific Ocean

AbstractThe northeast Pacific Coastal Temperate Rainforest (NPCTR) extending from southeast Alaska to northern California is characterized by high precipitation and large stores of recently fixed biological carbon. We show that 3.5 Tg‐C yr−1 as dissolved organic carbon (DOC) is exported from the NPCTR drainage basin to the coastal ocean. More than 56% of this riverine DOC flux originates from thousands of small (mean = 118 km2), coastal watersheds comprising 22% of the NPCTR drainage basin. The average DOC yield from NPCTR coastal watersheds (6.20 g‐C m−2 yr−1) exceeds that from Earth's tropical regions by roughly a factor of three. The highest yields occur in small, coastal watersheds in the central NPCTR due to the balance of moderate temperature, high precipitation, and high soil organic carbon stocks. These findings indicate DOC export from NPCTR watersheds may play an important role in regional‐scale heterotrophy within near‐shore marine ecosystems in the northeast Pacific.

Organic amendment effects on cropland soil organic carbon and its implications: A global synthesis

Increasing soil organic carbon (SOC) content can promote soil health and crop yield. Organic amendment application is a common practice to accelerate soil carbon sequestration in cropland. The effects of different organic amendments (e.g., compost, slurry) on SOC are uncertain. Previous studies have investigated SOC response to environmental factors but not well addressed the effect of organic amendment characteristics (e.g., source, liquid/solid form, pH). Depending on 1,972 comparisons from 424 articles, we undertook a meta-analysis approach to explore organic amendment effects on SOC content and the related influence factors. The results show that organic amendment addition increased SOC by an average of 26.9% (or 5.1 Mg C ha−1). Specifically, organic amendments can enhance SOC over the long term (>20 years) or within 1.0 m depth. Organic-residue inputs increased more SOC in regions with an arid climate, alkaline soils, or no-mineral nitrogen application soils than the humid climate regions, acidic soils, and nitrogen application soils, respectively. Sewage sludge and municipal solid waste as organic amendments led to high SOC. The organic amendments' pH and liquid/solid form caused significant differences in SOC accumulation. Amendments with a relatively low carbon content or rich nitrogen content have great potential to increase SOC storage. Our results illustrate the importance of amendment characteristics when estimating the potential of organic amendment addition to soil carbon accumulation. This study highlights that amendment application might be a sustainable strategy to increase soil carbon storage while promoting organic waste utilization.

A global meta-analysis of soil organic carbon in the Anthropocene

Anthropogenic activities profoundly impact soil organic carbon (SOC), affecting its contribution to ecosystem services such as climate regulation. Here, we conducted a thorough review of the impacts of land-use change, land management, and climate change on SOC. Using second-order meta-analysis, we synthesized findings from 230 first-order meta-analyses comprising over 25,000 primary studies. We show that (i) land conversion for crop production leads to high SOC loss, that can be partially restored through land management practices, particularly by introducing trees and incorporating exogenous carbon in the form of biochar or organic amendments, (ii) land management practices that are implemented in forests generally result in depletion of SOC, and (iii) indirect effects of climate change, such as through wildfires, have a greater impact on SOC than direct climate change effects (e.g., from rising temperatures). The findings of our study provide strong evidence to assist decision-makers in safeguarding SOC stocks and promoting land management practices for SOC restoration. Furthermore, they serve as a crucial research roadmap, identifying areas that require attention to fill the knowledge gaps concerning the factors driving changes in SOC.

Relationship between carbon pool changes and environmental changes in arid and semi-arid steppe—A two decades study in Inner Mongolia, China

As the arid and semi-arid grassland with the most extensive distribution area in northern China, the carbon stored in Inner Mongolia (IM) grassland is highly susceptible to environmental changes. With the global warming and drastic climate changes, exploring the relationship between carbon pool changes and environmental changes and their spatiotemporal heterogeneity is necessary. This study estimates the carbon pool distribution of IM grassland during 2003–2020 by combining the measured below ground biomass (BGB) dataset, measured soil organic carbon (SOC) dataset, multi-source satellite remote sensing data products, and random forest regression modeling method. It also discusses the variation trend of BGB/SOC and its correlation with critical environmental factors, vegetation condition factors and drought index. The results show that the BGB/SOC in IM grassland was stable during 2003–2020, with a weak upward trend. The correlation analysis reveals that high temperature and drought environment were unfavorable for developing vegetation roots and would lead to a decrease in BGB. Furthermore, temperature rise, soil moisture decrease, and drought adversely effected grassland biomass and SOC in areas with low altitude, high SOC density, suitable temperature and humidity. However, in areas with relatively poor natural environments and relatively low SOC content, SOC was not significantly affected by environmental deterioration and even showed an accumulation trend. These conclusions provide directions for SOC treatment and protection. In areas where SOC is abundant, it is important to reduce carbon loss caused by environmental changes. However, in areas with poor SOC, due to the high carbon storage potential of grasslands, carbon storage can be improved through scientifically managing grazing and protecting vulnerable grasslands.

The soil organic carbon: Clay ratio in North Devon, UK: Implications for marketing soil carbon as an asset class

AbstractBuilding up stocks of agricultural soil organic carbon (SOC) can improve soil conditions as well as contribute to climate change mitigation. As a metric, the ratio of SOC to clay offers a better predictor of soil condition than SOC alone, potentially providing a benchmark for ecosystem service payments. We determined SOC:clay ratios for 50 fields in the North Devon UNESCO World Biosphere Reserve using 30 cm soil cores (divided into 0–10 cm and 10–30 cm depth samples), with soil bulk density, soil moisture and land‐use history recorded for each field. All the arable soils exceeded the minimum desirable SOC:clay ratio threshold, and the ley grassland soils generally exceeded it but were inconsistent at 10–30 cm. Land use was the primary factor driving SOC:clay ratios at 0–10 cm, with permanent pasture fields having the highest ratios followed by ley grass and then arable fields. Approximately half of the fields sampled had potential for building up SOC stock at 10–30 cm. However, at this depth, the effect of land use is significantly reduced. Within‐field variability in SOC and clay was low (coefficient of variation was ~10%) at both 0–10 cm and 10–30 cm, suggesting that SOC:clay ratios precisely characterized the fields. Due to the high SOC:clay ratios found, we conclude that there is limited opportunity to market additional carbon sequestration as an asset class in the North Devon Biosphere or similar areas. Instead, preserving existing SOC stocks would be a more suitable ecosystem service payment basis.

Mapping soil organic carbon stocks in Nepal’s forests

Comprehensive forest carbon accounting requires reliable estimation of soil organic carbon (SOC) stocks. Despite being an important carbon pool, limited information is available on SOC stocks in global forests, particularly for forests in mountainous regions, such as the Central Himalayas. The availability of consistently measured new field data enabled us to accurately estimate forest soil organic carbon (SOC) stocks in Nepal, addressing a previously existing knowledge gap. Our method involved modelling plot-based estimates of forest SOC using covariates related to climate, soil, and topographic position. Our quantile random forest model resulted in the high spatial resolution prediction of Nepal’s national forest SOC stock together with prediction uncertainties. Our spatially explicit forest SOC map showed the high SOC levels in high-elevation forests and a significant underrepresentation of these stocks in global-scale assessments. Our results offer an improved baseline on the distribution of total carbon in the forests of the Central Himalayas. The benchmark maps of predicted forest SOC and associated errors, along with our estimate of 494 million tonnes (SE = 16) of total SOC in the topsoil (0–30 cm) of forested areas in Nepal, carry important implications for understanding the spatial variability of forest SOC in mountainous regions with complex terrains.

Evaluation of integrated crop management, organic management and natural farming in basmati rice-wheat system under Upper Indo-Gangetic Plains

Field experimentation was conducted to evaluate the comparative performance of integrated crop management, organic management and natural farming on crop growth, productivity, profitability and soil health under basmati rice-wheat system in Upper Indo-Gangetic Plains. Treatments comprised of different management practices viz. integrated crop management (ICM), organic management, natural farming (NF) and control (no nutrient) were used in experimentation. Plant height, number of effective tillers, SPAD meter reading, panicle weight, filled grains/panicle, fertility percentage and 1000-grains weight of basmati rice and wheat were observed highest under ICM followed by organic management. A significant reduction in growth and yield attributes was recorded under NF as compared to ICM and organic management. Grain yield of basmati rice was reduced by 15.2%, 51.2% and 53.9% under organic management, NF and control as compared to ICM, respectively. Similarly, 49.5%, 58.6%, and 63.8% reduction in grain yield of wheat was recorded under organic management, NF and control as compared to ICM, respectively. In comparison to ICM, system rice equivalent yield (REY) was reduced by 32.6%, 55.0%, and 59.0% under organic management, NF and control, respectively. Further, net return was 44.1% and 67.2% lower under organic management and NF as compared to ICM, respectively. Highest soil organic carbon (0.60%), available N, P, and K were found in organic management. Significantly highest soil microbial population, glomalin content and different soil enzyme activities were recorded under organic management. Overall, the integrated crop management provided balanced and continuous supply of the nutrient that resulted in higher productivity and profitability of basmati rice-wheat system.

Storage and controlling factors of soil organic carbon in alpine wetlands and meadow across the Tibetan Plateau

AbstractAlpine wetlands and meadows across the Three Rivers Source Region (TRSR) store high soil organic carbon (SOC). However, information on factors affecting SOC storage is scanty. Herein, we investigated SOC storage and explored factors affecting SOC storage, including climate, soil properties and above‐ and belowground biomass, using 50 soil profiles across the TRSR on the Tibetan Plateau. The SOC storage was 491.9 ± 158.5 Tg C and 545.2 ± 160.8 Tg C in the TRSR alpine wetlands and meadow, respectively. The SOC stock was positively correlated with the mean annual precipitation. However, no significant correlation between SOC stock and mean annual temperature was observed, as opposed to the global trend. In addition, SOC stock was positively correlated with both the aboveground biomass (AGB) and belowground biomass (BGB). Soil pH indirectly affected SOC stock, while SOC stock positively correlated with Al and Fe oxyhydroxides. Compared with vegetation biomass and climatic factors, soil properties, including soil pH and Al and Fe oxyhydroxides (Alo and Feo), affected not only SOC stock variation but also affected the impact of vegetation and climatic factors on SOC stock. Climate factors, AGB, BGB, soil pH, Alo and Feo jointly accounted for 59% of SOC stock variation in alpine wetlands and 64% of SOC stock variation in alpine meadow. This study suggests that soil properties are the dominant factors affecting SOC variation in alpine wetlands and meadow on the Tibetan Plateau.

Soil microorganism regulated aggregate stability and rill erosion resistance under different land uses

How microbial communities respond to soil aggregation and rill erosion resistance has rarely been addressed. Such a knowledge gap hinders the practice of guiding sustainable soil management. Herein, the community composition of bacteria and fungi was evaluated by 16S rRNA gene sequencing. We measured critical shear stress (τc) and rill erodibility (kd) by self-made jet device. The effects of microorganism on soil aggregation and rill erosion resistance were quantitatively analyzed under different land uses.The results indicated that the forest soil supported the colonization and enrichment of Acidobacteria and Basidiomycota on account of the unique vegetation and higher soil organic carbon (SOC). The forest and shrubland contained higher macroaggregate and mean weight diameter (MWD) than those of cropland and bare land, while rill erodibility (kd) was the opposite. MWD and kd had a negative power function (y = 105.64x−0.69). The biotic factors explained 73.50% of the variation in rill erosion resistance and soil aggregation, indicating microorganism are more important in acting on rill erosion resistance.This study suggests that SOC had strong regulatory effects on the soil key groups of bacteria and fungi assemblages; furthermore, their interaction facilitated the formation of stable macroaggregates. The stable macroaggregate structure and vegetation cover make the erodibility of forest soil at a relatively low level. However, cropland are not conducive to stability of aggregates, which easily causes soil erosion. Improving soil SOC and maintaining the relative abundance of key groups of microorganism would be conducive to soil sustainable developing.

Pelletized Straw Incorporation in Sandy Soil Increases Soil Aggregate Stability, Soil Carbon, and Nitrogen Stocks

In China, increasing the quantity and quality of total carbon and nitrogen stocks in sandy soil used for crop production is an important research issue. Soil amendment with pelletized straw could improve both soil physical structure and fertility in sandy soils, but these aspects remain understudied. The present pot and field experiments examined the dynamic changes in sandy soil water holding capacity, soil bulk density, soil total carbon and nitrogen stocks, and the distribution of water-stable aggregates and soil total carbon stocks related to aggregates across the following treatments: no fertilization (i.e., study control (CK)), normal fertilizer rate (NM), soil amendment at 150 Mg ha−1 (S150), manure amendment at 150 Mg ha−1 (M150), pelletized straw amendment at 75 Mg ha−1 (PS75), and pelletized straw amendment at 150 Mg ha−1 (PS150). The results show that the pelletized straw incorporation significantly increased water holding capacity and decreased soil bulk density. PS150 notably increased the large macroaggregates (&gt;2000 μm) proportion and decreased the ratio of &lt;250 μm aggregate size fractions in comparison with CK, NM, S150, and M150 at 0–20 and 20–40 cm soil depths. Compared with the CK treatment, the bulk soil carbon and nitrogen stocks in the 0–20 cm layers under the PS150 treatment were significantly increased by 85.2% and 302.9%, and in the 20–40 cm layers those increased by 136.4% and 257.1%, respectively. The PS150 treatment resulted in higher soil organic carbon (SOC) and particulate organic carbon content than the CK and PS75 treatments, whereas the PS75 treatment achieved maximum soil inorganic carbon content. The pelletized straw treatment increased the large macroaggregate-associated soil total carbon content at 0–20 and 20–40 cm soil depths. The maximum soil total carbon stocks were in the small macroaggregates (250 &lt; WSA &lt; 2000 μm) rather than in the large macroaggregate and microaggregates under the PS75 and PS150 treatments. Additionally, the pelletized straw and manure amendments increased the yield of silage corn, which was dependent on the increase in soil total carbon and nitrogen content in the macroaggregates, whereas the soil and manure amendments did not facilitate sandy soil aggregation and soil total carbon stock increases. In conclusion, PS150 was found to be the optimal amendment for maintaining sandy soil profile physico-chemical properties through macroaggregate stabilization. These results will be beneficial for arid and semi-arid regions, thus contributing to soil carbon and nitrogen conservation.