Soil Organic Carbon Levels Research Articles

Distribution of sequestered carbon in different pools in Alfisols under long-term groundnut system of hot arid region of India

Soil organic carbon (SOC) pools are indicators of soil productivity and sustainability and provide valuable information on the pathways of carbon sequestration in soils. We analysed organic C pools of different oxidizabilities, labile pools like particulate organic carbon, permanganate-oxidisable C, and microbial biomass carbon in soils under a long-term groundnut mono-cropping system with different management practices. Among the treatments, 50% NPK+farmyard manure (FYM) maintained a proportionately higher amount of soil carbon in passive pools (48.3%) followed by 50% NPK+ groundnut shell (GNS) (46.7%), FYM (44.7%), GNS (43.8%), 100% NPK (40.6%), 50% NPK (38.3%) and the control (32.4%). Particulate organic carbon fraction was the most sensitive fraction upon application of the amendments. Carbon stabilized from GNS and FYM sources had a skewed distribution along soil profile with a ratio of 1.2:1.0:1.4 and 1.8:1.0:1.3 at 0–15, 15–30, 30–45 cm depth, respectively. A critical carbon input of 0.32 Mg ha−1y−1 was needed to maintain SOC level, and the rate of conversion of crop residue C into soil organic C was about 8.1% for the present study. Combined use of chemical fertilizers and organic manure was found to be the best for enhancing SOC sequestration in groundnut mono-cropping system under hot arid eco-regions in India.

13C Labelling of Litter Added to Tea (Camellia sinensis L.) Plantation Soil Reveals a Significant Positive Priming Effect That Leads to Less Soil Organic Carbon Accumulation

Although annual return of litter occurs in tea (Camellia sinensis L.) plantations, the level of soil organic carbon (SOC) therein remains relatively low. The exact impacts of pruned litter on soil and its association with SOC accumulation in tea plantations remain unclear. In this study, we prepared 13C-labeled tea plant material and incubated it with soils collected at a tea plantation. Carbon dioxide (CO2) efflux and its sources were measured and distinguished based on the 13C isotopic method. Soil microbial community and the utilization of litter C were assessed by phospholipid fatty acid (PLFA) analysis combined with a stable isotope probing (SIP) technique. Litter incorporation initially significantly increased CO2 efflux. The majority of CO2 production (>90%) arose from native SOC mineralization, which was reflected by a strong positive priming effect (PE) that decreased over time. During the incubation period, β-glucosidase activity significantly decreased in both the control and litter-amended soil. A significant difference in the microbial community was observed between control and litter-amended soil, in which litter incorporation significantly increased the biomass of each microbial group relative to control soil. Based on PLFA-SIP, 78% of the C incorporated into individual microbes was derived from native SOC, while only 22% was derived from litter. Additionally, partial least squares regression path modeling (PLS-PM) revealed that the microbes associated with native SOC mineralization directly affected the changes in SOC (ΔCSOC+litter), whereas microbes related to litter degradation exhibited an indirect effect on ΔCSOC+litter by affecting β-glucosidase activity under litter incorporation. Taken together, SOC accumulated less in the tea plantation system despite the annual return of pruned litter to the field.

Potential Contribution of Groundnut Residues to Soil N and the Influence of Farmer Management in Western Uganda

Through symbiotic biological nitrogen fixation (BNF), grain legumes, such as groundnuts, can enhance soil nitrogen (N) and be an important source of N fertility, as well as a critical component of human nutrition and food security. Because legumes obtain N from soil N stocks as well as BNF, legume residues are key to capturing potential N benefits for soils, which may contribute to increased yields and food production. Here, we conducted a detailed survey at household and field level within a six-village corridor along the western boundary of Kibale National Park (KNP) in western Uganda. We focused on groundnut production and residue management practices and soil organic carbon (SOC) and total N (TN) in fields managed by 100 different households. We also determined SOC and TN in adjacent uncultivated KNP soils. We tested for relationships between socioeconomic factors and farmer groundnut management practices. We calculated a partial N balance and estimated potential N benefits under three scenarios for groundnut BNF. Within the study area, groundnut residue management varied greatly with 51% of surveyed farmers retaining residues on fields through spreading or incorporation, and 49% removing residues, either by transfer to banana groves or burning. Groundnut population density was relatively high with 43% of fields having >30 plants m−2. Despite providing net N inputs of up to 27 kg N ha−1, there was no observed effect of groundnut residue management practices on SOC, TN, or soil C:N ratios. Compared to uncultivated KNP soils, groundnut fields had lower mean levels of SOC and TN and wider C:N ratios. These values are consistent with cultivated soils; however, losses of SOC and TN were lower compared to losses previously reported for conversion from tropical forest to agricultural use. We found that farmer valuation and perception of groundnut residues were influential factors in residue management practices. Overall, we estimated that groundnut residues have the potential to contribute to SOC and TN stocks if retained in the field, but, conversely, removal will result in sizable losses. We find that both environmental and social contexts must be considered when recommending legumes for N provisioning services.

Soil organic carbon dynamics in the agricultural soils of Bangladesh following more than 20 years of land use intensification

Soil organic carbon (SOC) is a key soil quality indicator, as it is a source and storage of plant nutrients and plays a vital role in soil fertility and productivity maintenance. Intensification of agriculture is known to cause SOC decline; however, much of the evidence stems from field-scale experimental trials. The primary aim of this study is to investigate how more than 20 years of agricultural land use intensification in Bangladesh has influenced SOC levels at landscape levels. This was achieved by revisiting in 2012 four sub-sites from the Brahmaputra and Ganges alluviums which were previously sampled (1989–92) by the Soil Resource Development Institute and collecting 190 new samples. These were located at different elevations and subjected to differing amounts of inundation. The SOC was determined using the same method, potassium dichromate wet oxidation, used in the 1989-92 campaign. A comparison of the SOC in the 2012 samples with their historic levels (1989–92) revealed that overall SOC declined significantly across both alluviums as well at their four sub-sites. Further analysis, however, showed that SOC has declined more at higher sites. The higher sites are inundated to a limited level, which makes them suitable for growing multiple crops. Among the land types considered here, the low land sites (because of their topographical position) remain inundated for a greater part of the year, allowing a maximum of only one crop of submerged rice. As a result of reduced biomass decomposition due to anaerobic conditions when inundated, and lower land use/cropping intensity, SOC accretion has occurred in the lower land sites.The SOC levels in South Asian countries are inherently low and agricultural land use intensification fuelled by growing food production demand is causing further SOC loss, which has the potential to jeopardise food security and increase the environmental impact of agriculture.

Soil organic carbon stock in arid and semi-arid steppe rangelands of North Africa

The assessment of soil organic carbon stock (SOCS) in degraded and rehabilitated soils in steppelands and rangelands of North Africa is crucial for the adoption of adequate management strategies that respond to sustainable development. This study aimed to estimate the SOCS in the surface layer of soils rehabilitated by prickly pear plantations (PPP) and analyze the effects of edaphic factors controlling the variation of SOCS in old PPP (OPPP), young PPP (YPPP) and control plots (unplanted plots). Under arid and semi-arid climates, three steppe sites were sampled in which three plots with OPPP (age = 10–20 years), YPPP (age < 5 years) and controls plots were considered. In each plot, five quadrats were delimited and within each quadrat, two pedological profiles were dug to collect soil samples. The determined parameters were soil organic carbon (SOC), bulk density (BD), pH, electrical conductivity (EC) and total calcium carbonate. The averages of SOCS varied between 14.51 ± 11.03 t/ha (min–max: 0.09–35.88 t/ha) under arid climate and 17.32 ± 9.05 t/ha (range: 0.26–41.84 t/ha) under semi-arid climate. The variations of SOCS were significant (P = 0.002) between the type of steppe managements but not significant (P > 0.05) among climate zones. Generally, the control plots and OPPP stored more carbon (14–19 t/ha) than steppes with YPPP (11–14 t/ha). SOCS varied significantly with changes in soil depths, it reached 27 t/ha at 15 cm and dropped to 10–18 t/ha at 20 cm. Regardless of the type of climate and rangeland management, SOCS evolved with BD and soil organic matter. This study estimated for the first time the SOCS in soils of degraded steppe rangelands in North Africa. Even if the SOCS remains low degraded steppes rangelands, it is necessary to avoid the loss of SOC in these ecosystems. The adoption of conservation agricultural practices, e.g. organic matter addition and reduced tillage techniques can increase SOC levels in these ecosystems.

Soil texture controls added organic matter mineralization by regulating soil moisture—evidence from a field experiment in a maritime climate

Soil organic carbon (SOC) levels generally increase with increasing clay and silt content under similar climatic conditions because of increased physicochemical protection. Surprisingly though, many silt loam soils in Western Europe have low top SOC levels compared to coarser textured soils. Soil texture also strongly controls soil moisture with consequent indirect impact on heterotrophic activity. Especially during periods of prolonged drought, which seem to be occurring more frequently throughout Europe, it could be expected that this soil textural control of moisture retention decisively affects added organic matter (OM) decomposition. We hypothesized that, contrary to expected textural effects on physicochemical protection of OM, the higher moisture availability in silty soils strongly favors added OM mineralization during periodic drought than sandy soils. Moreover, as a secondary objective, we investigated if during prolonged drought, capillary moisture supply could significantly alleviate the water stress on added OM decomposition in sand with rather shallow groundwater table. Therefore, we established a one-year field trial in which the upper 0.5 m soil layer was replaced by sand, sandy loam and silt loam soil with low SOC. In a fourth treatment, a gravel layer was added beneath the sand layer to exclude capillary rise. Maize residues were mixed homogenously with soil in top 25 cm in all plots. Changes in soil moisture and maize-C mineralization (Cmaize-min) were measured. We found that soil texture did not affect Cmaize-min until after about five months and thereafter Cmaize-min rates were higher in the silt loam than in the sandy soils. Moisture content correlated positively with the Cmaize-min rate for the sand-textured soils only. Capillary rise did not result in a significant increase in Cmaize-min in the sandy soil. After one year, a larger share of added Cmaize was mineralized in the silt loam soil (81 ± 6%) than in the sandy soil (56 ± 7%). These results clearly highlight that soil texture controlled Cmaize-min indirectly through regulating moisture under the field conditions when the study area faced a period of unusual drought. Moreover, our results imply that, under future climate scenarios, more frequent droughts might lead to a lesser SOC depletion in sandy soils compared to in finer textured soils under similar management.

Using Ecological Site Descriptions to make ranch-level decisions about where to manage for soil organic carbon

Maintaining and enhancing soil organic carbon storage can mitigate climate change while promoting forage growth. California has adopted incentive programs to promote rangeland practices that build soil organic carbon. However, there is no standard framework for assessing the baseline level of soil organic carbon at the ranch scale. Here, we use the Ecological Site Description — a land-type classification system — to help ranch managers set priorities about where to implement practices to increase soil organic carbon. We measured baseline carbon stocks at 0 to 15 and 15 to 30 centimeters' depth across three ecological sites and two vegetation states (shrubland and grassland) at Tejon Ranch, California. We discovered increased levels of soil carbon at ecological sites in higher elevations, and more soil carbon in shrublands as compared to grasslands. Slope, elevation, and soil texture, as well as plant litter and shrub cover, were significant predictors of soil carbon. The Ecological Site Description framework can serve as an important tool to help range managers keep carbon in the soil and out of the atmosphere.

EFFECT OF KITCHEN WASTE COMPOST ON TOMATO YIELD AND CARBON ACCUMULATION IN SOIL

Two years field study was conducted on the effect of kitchen waste compost on tomato yield and carbon accumulation in soil at Regional Agricultural Research Station (RARS), Jamalpur, Bangladesh under Old Brahmaputra Floodplain (AEZ 9) during rabi season of 2020-2021 and 2021-2022. The objectives were to determine whether composted kitchen waste would increase soil organic carbon levels and tomato yield. The BARI tomato-21 was utilized as the test crop, and the experiment was set up using a randomized complete block design (RCBD) with three replications. There were seven treatments comprising T1 = 100 % RDCF (control), T2=100 % RDCF + Kitchen Waste Compost @ 2.5 t ha-1, T3 = 100 % RDCF + Kitchen Waste Compost @ 5 t ha-1, T4 = 85% RDCF + Kitchen Waste Compost @ 2.5 t ha-1, T5 = 85% RDCF + Kitchen Waste Compost @ 5 t ha-1, T6 =70% RDCF + Kitchen Waste Compost @ 2.5 t ha-1 and T7 = 70% RDCF + Kitchen Waste Compost @ 5 t ha-1. Data revealed that, combined application of kitchen waste compost and chemical fertilizer increased tomato production as compared to sole application of chemical fertilizers. The highest average tomato fruit yield (68.46 t ha-1) was found in T3 treatment (100 % RDCF + Kitchen Waste Compost @ 5 t ha-1). T1 treatment (100 % RDCF) yielded 55.82 t ha-1 of tomatoes, indicating that plants could not receive enough nutrients from a single application of chemical fertilizer. On the other hand, as chemical fertilizers were reduced, tomato yield gradually declined. The T6 treatment (70 % RD + kitchen waste compost @ 2.5 t ha-1) had the lowest average tomato output, 52.73 t ha-1. The T3 treatment (100 % RDCF + kitchen waste compost @ 5 t ha-1) performed better after the second cycle was finished in terms of total nutrient content in post-harvest soil. In comparison to previous treatments, this treatment also increased soil carbon accumulation. As a result, it is practicable to apply the full dose of chemical fertilizer with 5 t ha-1 kitchen waste compost, which will boost tomato yields, bring about economic benefits and prevent soil and environmental contamination.

陇东雨养苹果覆膜对土壤团聚体结构稳定性与细根分布的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 陇东雨养苹果覆膜对土壤团聚体结构稳定性与细根分布的影响 DOI: 10.5846/stxb202102190468 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31760555）；财政部和农业农村部：国家现代农业产业技术体系（GARS-27）；农业农村部西北地区果树科学观测实验站（S-10-18） Effects of film mulching on soil aggregate structure stability and fine root distribution of rain-fed apple in eastern Gansu Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:不同的果园管理方式可影响果树根系生长、分布与土壤团聚体稳定性、有机碳固存，进而改变"根-土"复合体响应关系。对西北陇东旱塬不同覆膜年限（2 a、4 a和6 a）苹果园表层土壤（0-20 cm）细根生长进行调查，并采用干筛法和湿筛法相结合的方式对土壤团聚体进行分级（>2 mm，0.5-2 mm，0.25-0.5 mm和<0.25 mm）。计算团聚体稳定性参数[> 0.25 mm机械稳定性团聚体含量（DR0.25）、> 0.25 mm水稳性团聚体含量（WR0.25）、平均重量直径（MWD）、平均几何直径（GMD）、团聚体破坏率（PAD）、水稳系数（WSC）]和团聚体有机碳含量。分析细根生长与土壤物理结构对长期覆膜的响应，探明土壤团聚体稳定性与有机碳固持关系，揭示黄绵土物理结构稳定机制。结果表明：6 a处理通过增加表层土壤黏粒和物理性黏粒比例，改变孔隙结构，抑制细根生长，其根量、根长和根表面积仅为对照（CK）的20.97%、24.66%和41.25%；降低表层土壤团聚体力稳性，其DR0.25、机械稳定性团聚体MWD和GMD仅为CK的82.2%、74.02%和59.38%；对水稳性团聚体的保护作用低于短期覆膜（2 a），其PAD和WSC为2 a处理的121.17%和54.56%。2 a处理可提高土壤团聚体的力稳性、水稳性和土壤团聚程度，使土壤结构得到改善。同时对机械稳定性、水稳性团聚体有机碳提升效果优于6 a处理，为6 a处理的115.66%和116.6%。大团聚体固持有机碳能力高于微团聚体，但由于长期覆膜团聚体稳定性的下降，6 a处理的DR0.25为CK的82.2%，不利于对有机碳的保护，使土壤有机碳水平对团聚体稳定性变异决定性仅为29.55%。连续覆膜引发的频繁干湿交替增加了黏粒对土壤结构稳定性的影响权重，促使表土"隐形"退化，抑制苹果细根在表层土壤中的生长、分布。2 a处理对土壤团聚体结构有良好的保护作用，促进土壤有机碳累积。 Abstract:Different orchard management methods can affect the growth and distribution of fruit roots, the stability of soil aggregates and the ability of organic carbon storage, and then change the response relationship of root-soil complex. The fine root growth of apple orchard surface soil (0-20 cm) with different plastic film mulching years (2 a, 4 a, and 6 a) was investigated in the dry tableland of Longdong, Northwest China. The combination of dry and wet screening methods was used to classify soil aggregates (>2 mm, 0.5-2 mm, 0.25-0.5 mm, and <0.25 mm). The aggregate stability index, including > 0.25 mm Mechanical stability aggregates content (DR0.25), > 0.25 mm water-stabled aggregates content (WR0.25), Mean weight diameter (MWD), geometric mean diameter (GMD), percentage of aggregate destruction rate (PAD), water stability coefficient (WSC), and the content of organic carbon were calculated. The response of soil physical structure and fine root growth to long-term film mulching was analyzed, the relationship between soil aggregate stability and organic carbon sequestration was explored, and the stability mechanism of physical structure of loess soil was revealed. The results showed that film-mulching six years inhibited fine root growth by increasing soil clay, the proportion of physical clay and changing pore structure, and the root weight, root length and root surface area were only 20.97%, 24.66% and 41.25% of conventional tillage (CK); The DR0.25, MWD and GMD of surface soil aggregates were 82.2%, 74.02% and 59.38% of CK; The protective effect of PAD and WSC were 121.17% and 54.56% of film-mulching two years, compared with that of short-term film mulching. Film-mulching two years improved the force stability and water stability of soil aggregates as well as the degree of soil aggregates, and improved the soil structure. At the same time, the organic carbon improvement effect of mechanical stability and water stability aggregates was better than that of film-mulching six years, which was 115.66% and 116.6% of film-mulching six years. Although the ability of large aggregates to hold organic carbon was higher than that of micro aggregates, due to the long-term stability decline of coated aggregates, the DR0.25 of film-mulching six years was only 82.2% of CK, which was not conducive to the protection of organic carbon, so that the decisive effect of soil organic carbon level on the stability variation of aggregates was only 29.55%. The frequent dry-wet alternation caused by continuous film mulching increased the influence weight of clay particles on soil structural stability, promoted the invisible degradation of the topsoil, and inhibited the growth and distribution of fine roots of apple in the topsoil. Film-mulching two years had a good protective effect on soil aggregate structure and promoted soil organic carbon accumulation. 参考文献 相似文献 引证文献

Bioenergy sorghum’s deep roots: A key to sustainable biomass production on annual cropland

AbstractBioenergy sorghum has high biomass yield potential, drought resilience, good nitrogen use efficiency, and a root system that contributes to the accumulation of soil organic carbon. In this study, field grown bioenergy sorghum root systems were analyzed during the growing season to characterize their depth, biomass, morphology, anatomy, and gene expression profiles. Bioenergy sorghum roots grew continuously during a 155‐day growing season producing ~175 nodal roots, accumulating ~7 Mg of dry biomass per hectare, and reaching &gt;2 m deep in the soil profile. Nodal roots within 20 cm of the stem were 1–5 mm in diameter, whereas roots deeper in soil profiles were enriched in lateral roots with small diameters (~30–500 µm) enabling growth through soil macropores. In older field‐grown plants, roots with intact endodermal, vascular and inner root tissues were surrounded by degraded or aerenchyma‐filled epidermal and cortical cell layers. Transcriptome analysis of nodal, surface, and deep roots identified &gt;2,500 differentially expressed genes involved in root growth, transport, adaptation, defense, and AMF–root interaction. Deep roots (180–240 cm) differentially expressed genes that regulate lateral root growth. Surface roots (0–20 cm) located mid‐row differentially expressed genes involved in nitrate transport, whereas ammonium transport genes were expressed in surface and deep roots and genes involved in phosphate transport were expressed in nodal, surface, and deep roots. Overall, bioenergy sorghum's long growing season enables root systems to grow deeper and accumulate more biomass than annual grain crops such as maize, attributes that could help restore annual cropland soil organic carbon levels and improve soil productivity. Deep roots active in nutrient transport are positioned to take‐up fertilizer leached deep into soil profiles mitigating potential nutrient run‐off. Bioenergy sorghum's large and deep root system is a key to sustainable production of biofuels, biopower, and bioproducts on annual cropland.

Combined application of animal manure and stover enhance labile organic carbon and benefit the microbial community in dark brown soil

ABSTRACT Returning organic materials is recognized as an effective practice to alter soil organic carbon (SOC) content, in which microorganisms play a critical role. The objective of this study was to evaluate the effects of different kinds of animal manure combined with stover (AM-S treatments) on labile organic C fractions and soil microbial community. The two-year experiment involved four treatments: maize stover only (S), maize stover plus ox manure (SO), maize stover plus chicken manure (SC), and maize stover plus pig manure (SP). In 2018 and 2019, AM-S treatments increased the levels of SOC, dissolved organic carbon (DOC), easily oxidized carbon (EOC), microbial biomass carbon (MBC), and maize yields. Maize stover plus ox manure treatment could provide better accumulation of MBC, and enhance bacterial and fungal richness and diversity. Maize stover plus pig manure treatment enhanced the contents of DOC and maize yield and also recorded the highest percentage of Proteobacteria (57.6%). Also, the EOC contents were 13.0% and 21.5% higher than SO and SC respectively. In all, our findings suggested that the application of maize stover plus pig manure was the most effective treatment for enhancing labile SOC fractions and improving the microbial community.

Soil Organic Carbon Content Prediction Using Soil-Reflected Spectra: A Comparison of Two Regression Methods

Quantifying the organic carbon content of soil over large areas is essential for characterising the soil and the effects of its management. However, analytical methods can be laborious and costly. Reflectance spectroscopy is a well-established and widespread method for estimating the chemical-element content of soils. The aim of this study was to estimate the soil organic carbon (SOC) content using hyperspectral remote sensing. The data were from soils from two localities in the semi-arid region of Brazil. The spectral reflectance factors of the collected soil samples were recorded at wavelengths ranging from 350–2500 nm. Pre-processing techniques were employed, including normalisation, Savitzky–Golay smoothing and first-order derivative analysis. The data (n = 65) were examined both jointly and by soil class, and subdivided into calibration and validation to independently assess the performance of the linear methods. Two multivariate models were calibrated using the SOC content estimated in the laboratory by principal component regression (PCR) and partial least squares regression (PLSR). The study showed significant success in predicting the SOC with transformed and untransformed data, yielding acceptable-to-excellent predictions (with the performance-to-deviation ratio ranging from 1.40–3.38). In general, the spectral reflectance factors of the soils decreased with the increasing levels of SOC. PLSR was considered more robust than PCR, whose wavelengths from 354 to 380 nm, 1685, 1718, 1757, 1840, 1876, 1880, 2018, 2037, 2042, and 2057 nm showed outstanding absorption characteristics between the predicted models. The results found here are of significant practical value for estimating SOC in Neosols and Cambisols in the semi-arid region of Brazil using VIS-NIR-SWIR spectroscopy.

Ameliorating soil structure for the reservoir riparian: The influences of land use and dam-triggered flooding on soil aggregates

Soil aggregates are considered to be strongly influenced by land use and hydrological regime. Yet, the relative importance of land use and flooding intensity on soil aggregate stability (SAS) in riparian zones remains unclear. Hence, the objective of this study was to examine the effects of land use and flooding intensity on SAS, as well as the aggregate-associated organic carbon (C) and nitrogen (N) contents in the riparian zone along the Three Gorges Reservoir of Yangtze River, China. In 2019, during the reservoir discharge period when the reservoir is at the lowest water level, SAS and aggregate-associated organic C and N contents were investigated along a gradient of the flooding intensity across riparian zones with different restoration practices, including natural grasslands, artificial mixed forests consisting of flood tolerant plants (mulberry and metasequoia), and transplanted lotus. Croplands (i.e., corn, paddy and peanut fields) at different elevations above sea level were used as references. The results showed that artificial mixed forests were more effective in improving the SAS than natural grasslands at elevations above 173 m, while natural grasslands were more effective in improving the SAS than artificial mixed forests and lotus at elevations below 173 m. However, riparian soil stability cannot be simply explained by land use management only, but rather the coupling effects of land uses and flooding intensity. Variation partitioning analysis showed that dam-triggered flooding intensity (21.5%) contributed more than land use (15.5%) in explaining riparian SAS. Also, the soil organic carbon (SOC) and total nitrogen (TN) had significantly positive correlations with the proportion of large macroaggregates (>2 mm) and SAS, indicating that maintaining higher levels of SOC and TN via the development of land use strategies commensurate with the flooding intensity was conducive to the formation and stability of soil aggregates. Meanwhile, the relative contribution of microaggregates (<0.053 mm) to bulk SOC or N content decreased with elevation. Therefore, the finding provides new insights into the focus of C sequestration, and suggests that C assessment should be shifted to microaggregates in the riparian zone. Overall, our study highlights that different land use strategies should be conducted for different elevations to promote SAS, aggregate-associated C and N accumulation in the riparian zone, which can provide a reference for ecological restoration in areas experiencing similar conditions.

Global variation in soil carbon sequestration potential through improved cropland management.

Widespread adoption of improved cropland management measures is advocated to increase soil organic carbon (SOC) levels, thereby improving soil fertility and mitigating climate change. However, spatially explicit insight on management impacts is limited, which is crucial for region‐specific and climate‐smart practices. To overcome these limitations, we combined global meta‐analytical results on improved management practices on SOC sequestration with spatially explicit data on current management practices and potential areas for the adoption of these measures. We included (a) fertilization practices, i.e., use of organic fertilizer compared to inorganic fertilizer or no fertilizer, (b) soil tillage practices, i.e., no‐tillage relative to high or intermediate intensity tillage, and (c) crop management practices, i.e., use of cover crops and enhanced crop residue incorporation. We show that the estimated global C sequestration potential varies between 0.44 and 0.68 Gt C yr−1, assuming maximum complementarity among all measures taken. A more realistic estimate, not assuming maximum complementarity, is from 0.28 to 0.43 Gt C yr−1, being on the lower end of the current range of 0.1–2 Gt C yr−1 found in the literature. One reason for the lower estimate is the limited availability of manure that has not yet been recycled. Another reason is the limited area for the adoption of improved measures, considering their current application and application limitations. We found large regional differences in carbon sequestration potential due to differences in yield gaps, SOC levels, and current practices applied. The highest potential is found in regions with low crop production, low initial SOC levels, and in regions where livestock manure and crop residues are only partially recycled. Supporting previous findings, we highlight that to encourage both soil fertility and SOC sequestration, it is best to focus on agricultural soils with large yield gaps and/or where SOC values are below levels that may limit crop production.

Comparative study of methane emission in the reclamation-restored wetlands and natural marshes in the Hangzhou Bay coastal wetland

Wetlands play a crucial role in reducing global warming potential in response to global climate change. Large-scale reclamation and artificial restoration of coastal wetlands significantly affect the greenhouse gas methane emissions of coastal ecosystems. To comprehensively understand the difference in methane emissions between natural and reclamation-restored wetlands, the natural bare mudflat (BM – bare mudflat) in Hangzhou Bay, three types of natural vegetation wetlands (SM - Scirpus mariqueter, PA – Phragmites australis, and SA – Spartina alterniflora), and four types of reclamation-restored P. australis wetlands with different water levels (RW0 – Water level at 0 cm; RW10 – Water level at 10 cm; RW20 – Water level at 20 cm; RW30 – Water level at 30 cm) were selected to analyze the relationship between methane emissions and environmental factors through field observations and laboratory experiments. The results showed that the methane emission flux and methane production potential (MPP) of reclamation-restored wetlands were notably higher than those of natural wetlands, and the monthly dynamics in the different types of wetlands were consistent with temperature. The methane emission flux increased rapidly from April to July (summer), and reached a monotonic peak in July. Among the natural wetlands, the methane emission flux and MPP of SA were significantly higher, which was mainly driven by the soil organic carbon (SOC). In the reclamation-restored wetlands, the methane emission fluxes did not significantly differ between RW10, RW20, and RW30, but were remarkably higher than those of RW0 and natural wetlands, which was mainly driven by the water level and salinity. The differences in the MPP of the different soil layers were mainly affected by the SOC and water levels. Especially in the 0–5 cm surface soil layer of the reclamation-restored wetlands, the MPP was significantly higher, which was mainly driven by the SOC. Therefore, during the later stages of artificial reclamation-restored wetlands, appropriate water level and salinity management and other effective engineering measures should be explored to manage methane emissions during wetland restoration.

Impact of sustainable land‐use management practices on soil carbon storage and soil quality in Goa State, India

AbstractEvaluating sustainable land management (SLM) practices have regional to worldwide implications. It is imperative to develop SLM under particular soil type, climate, and cropping sequence following area‐specific best management practices to harness maximum profitability. The alternative land‐use system (ALUS—natural forest, pasture, cashew, areca nut, coconut) on hills and agricultural land‐use system (AGLUS—rice–rice, rice–pulse) in the coastal plains of Goa State in west coast India were evaluated in this study. This study assessed the impact of sustainable land‐use management practices on different fractions of soil organic carbon (SOC), its stock, and soil quality index (SQI) under the ALUS and AGLUS. The total SOC stocks under different land‐use systems varied from 14.4 Mg C ha−1 in rice–rice rotations to 133.7 Mg C ha−1 in cashew. The lability index, available nutrients, and biochemical properties were higher in ALUS. The variation in the levels of SOC and soil quality was due to land use and management practices. The results indicated land use with areca nut (SQI = 0.8) on the hills and rice–pulses (SQI = 0.25) rotations on the coast had maintained soil quality of high order. We recommend promoting sustainable agriculture with ALUS on the hills and AGLUS on the coastal plains of Goa State to enhance SOC storage, improve soil quality, and increase farmers' income.

Do interactions between application rate and native soil organic matter content determine the degradation of exogenous organic carbon?

Although the amendment of various forms of exogenous organic matter (EOM) is a common practice in cropland production, it is to date not clear if its mineralisation in soil depends on application rate. Previous research suggested that spatial concentration of EOM in soil positively impacts its degradability. Here, we seek to test these reports and furthermore to investigate if an interactive effect exists with native soil organic carbon (SOC) concentration. We hypothesised that at a low EOM dose, more EOM remains undecomposed in soil and that this effect becomes stronger at lower SOC level. Moreover, as a secondary goal, we explored if priming of native SOC mineralisation depends on EOM dose. Therefore, we set up seventy-day soil incubation experiments with six varying C4-maize residue (δ13C = −12.7‰) doses (0–6 g kg−1) in soil mesocosms of loamy sand subsoils (δ13C = −25.7‰) with three different native SOC levels (i.e. 0.1, 0.5, and 1.0%). Soil CO2 emissions and isotopic signature measurements of CO2 allowed to discern EOM and SOC mineralisation. We found that EOM-derived C mineralisation increased proportionally to EOM dose, refuting the hypothesised relative undecomposed EOM at low concentration. Volumes of larger pore neck size diameter classes (60–100 and >300 μm) almost doubled at high EOM dose, demonstrating formation of macropores. Yet, this apparently did not impact EOM mineralisation, probably because O2 supply was always sufficient to allow unlimited activity of EOM degraders, even at higher EOM doses, as indicated by generally higher measured redox potential. With EOM dose, fungal marker PLFA abundances increased in the 1% SOC soil and protozoan abundances increased in all three soils, but apparently these shifts did not result in an enhanced relative degradation of the EOM. Increasing EOM doses induced negative priming, e.g. EOM ≥1 g kg−1 reduced SOC mineralisation by >43% and >24% compared to the control in the 0.1 and 0.5% SOC soils, respectively; whereas no priming occurred in soil with 1% SOC. These results were largely explained by the amount of added C relative to microbial biomass carbon, and the theorised switch of slow decomposers (so called K-strategists and involved in recalcitrant compound decomposition) from SOM to preferentially decompose EOM at higher doses. We also postulate that at low SOC %, the obvious increased O2 consumption with higher EOM dose more readily results in local anaerobic conditions in finer pores, i.e. where SOC is located and mineralised. We conclude that on the short term, agricultural management for SOM thus does not need to consider EOM doses but only the total amount of EOM.

Effects of fire on soil organic carbon, soil total nitrogen, and soil properties under rotational shifting cultivation in northern Thailand

Fire has been used for land clearing under rotational shifting cultivation (RSC) in Northern Thailand for a long time. However, the effects of fire on soil organic carbon (SOC), soil total nitrogen (STN), and soil properties are not well understood. We determined SOC, STN, and soil properties of the topsoil layer (0–30 cm) along a fallow chronosequence under RSC and assessed how fire affects SOC, STN, and soil properties. Eight fields at Ban Mae Pok, Mae Chaem District, Chiang Mai Province, Northern Thailand, were investigated. The levels of SOC, STN, and soil properties were observed at three time points: pre-burning, post-burning (5 minutes after burning), and post-harvest (nine months after burning). The highest SOC and STN stocks, organic matter (OM), and clay content were observed for the longest fallow period (7 years fallow), whereas the shortest period (1 year fallow) resulted in the lowest SOC and STN stocks. Fire caused no significant changes in SOC, STN, and some soil properties (soil texture, available P, exchangeable K, exchangeable Ca, exchangeable Mg, bulk density, and OM) because of the low fire intensity and short fire duration. Only pH and electrical conductivity were significantly increased (p ≤ 0.05) after burning due to the demobilization of base cations in burnt vegetation and incorporation into the soil with ashes and wood charcoal. Although fire may still be necessary for RSC, maintaining the fire intensity below 380 °C to reduce SOC losses and appropriate post-fire management strategies to reduce STN losses are crucial.

Prospects for soil carbon storage on recently retired marginal farmland

Soil organic carbon (SOC) is strongly affected by farm cropping, which covers >10% of the earth's surface. Land retirement of marginal fields, now a global initiative, can increase SOC storage but reported accumulation rates are variable. Here, we quantify SOC in crop fields and retired marginal land in an intensely farmed 10,000 km 2 region of central North America, testing nutrients, soil texture and management as drivers of SOC storage. Overwhelmingly, SOC was associated with farm management with among-farm differences varying >fourfold (17.4–81 t ha −1) in the top 15 cm. Total farm SOC averaged 502.2 t farm −1 but again ranged widely (216–1611 t farm −1). Farm-specific SOC was often, but not always, higher on farms with N-rich silt-clay soils, and lower on sandy soils with higher P relating to former tobacco production. In contrast, within-farm SOC between crop fields and retired land did not significantly differ with time. Low SOC on retired lands was associated with persistently high soil N and P and elevated microbial respiration. Retired soils did possess substantially larger pools of lignin-rich root biomass to depths of 60 cm, which may signify eventual SOC accumulation possibly as nutrient legacies diminish. Our work shows that management legacy, interacting with soil texture and nutrients, predicts SOC more than short-term retirement. Indeed, crop fields averaged 67% of farm SOC because they represented up to 94% of total farm area – SOC retention on cropland remains a management priority, above and beyond gains with retirement. Interestingly, the largest per-volume SOC levels were in remnant forest that contained 25% of farm SOC despite only averaging 11% of farm area. Maintaining SOC stocks in farm landscapes may be more quickly attained by protecting remnant forest, with retired lands needing time to re-build SOC stocks.

Soil Organic Carbon and System Environmental Footprint in Sugarcane-Based Cropping Systems Are Improved by Precision Land Leveling

A six-year experiment (2009 to 2015) was conducted on sugarcane-based cropping systems in farmers’ fields to examine the effects of precision land leveling (PLL) compared to traditional land leveling (TLL) in terms of soil organic carbon (SOC), greenhouse gas emissions, irrigation water requirements, and system productivity and profitability. Twelve treatments compared different sugarcane sowing regimes and crops in rotation under both PLL and TLL. Spring-sown sugarcane grown in rotation with rice, potato, and wheat under PLL had the highest production (89.7 kg ha−1 day−1) and required 142 cm irrigation water, which was 35.1% less water than a commonly practiced cropping system with late-sown sugarcane grown in rotation with rice and wheat only under TLL). Cropping systems established under PLL had higher land use efficiency (ranging between 64.9 and 86.2%), higher energy productivity (90.7 to 198.6 GJ ha−1), and lower greenhouse gas emissions (5249.33 to 944.19 kg CO2 eq ha−1 year−1) than those under TLL. As well, treatments under PLL had increased levels of SOC, particularly in the upper soil layers, relative to SOC in treatments under TLL. Combining PLL with diversification of crops in sugarcane cropping systems has the potential to sustainably increase farmers’ land productivity and profitability while improving soil health and reducing irrigation requirements. These benefits are likely to have applications in other sugarcane-based cropping systems in similar agro-ecologies.