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The determination of changes in soil organic carbon (SOC) content under different cropping systems is necessary for policy development oriented towards soil conservation, C sequestration, and future C credit markets. The aim of this study was to generate an open SOC dataset resulting from a systematic literature search related to the agricultural systems for Southeast Asia. The dataset has 209 articles and 4341 observations on soils of cropping systems in this region from articles published between 1987 and 2023. This dataset included different management practices, land uses, soil sampling depth, and length of SOC content assessment. In addition, inherent features of crop production reported in the experiments were included in the dataset. This dataset can be applied to quantify and compare the impact of different land uses or management practices on SOC content, providing foundational knowledge towards identifying sustainable practices. Lastly, it is a useful guide for future regional SOC sequestration policies and the development of C credit markets. [ABSTRACT FROM AUTHOR]

Cambodia has faced drastic agrarian changes over the last twenty years with a rapid and massive transformation of the uplands from forest into arable land. Soil quality depletion is one of the main drivers of the resulting decline in crop productivity and increasing production costs in the uplands of Battambang province. The objective of the study was to assess the early effects of conventional plough-based (20 cm) management (CT) and two conservation agriculture-based (CA) cropping systems (the use of a single--CAS vs. multiple cover crop species--CAM) on a maize monocropping system using three soil organic carbon (SOC) fractions on Mollisols in Battambang province. SOC content, permanganate oxidizable carbon (POXC) and soil CO2 basal respiration through SituResp® were recorded at a depth of 0-10 cm. Twelve sampling periods were used over the growth period of the cover crops and during the maize cycle. POXC and SituResp® were highly sensitive to management practices with, across the 12 sampling periods, higher values (p < .05) under CA than CT, with an average increase of 6% and from 20% to 23%, respectively. No difference was observed in SOC content between the practices in our sampling periods. Seasonal variations were observed in both POXC and SituResp®. POXC underwent larger fluctuations following critical weather events than SituResp®. This study showed that POXC and SituResp® were rapidly sensitive to changes in agricultural management practices. POXC and SituResp® are largely influenced by seasonality and could help clarify the impact of weather patterns on soil C dynamics. [ABSTRACT FROM AUTHOR]

Highlights: [•] No soil disturbance and high biomass-C input contribute to C sequestration in long-term no-till. [•] Continuous C flow from crop residues increases labile C and addresses C migration to mineral associate-C. [•] Preserving surface-soil C fractions and labile C increases SOC stock, and restores soil resilience. [•] SOC stock and labile C increases enhance the relationship with agronomic productivity in long-term no-till. [ABSTRACT FROM AUTHOR]

Agricultural practices should modify the diversity of soil microbes. However, the precise relationships between soil properties and microbial diversity are poorly known. Here, we study the effect of agricultural management on soil microbial diversity and C turnover in tropical grassland of north-eastern Laos. Three years after native grassland conversion into agricultural land, we compared soils from five land use management systems: one till versus two no-till rotational cropping systems, one no-till improved pasture and the natural grassland. Soils were incubated in microcosms during 64 days at optimum temperature and humidity. Bacterial and fungal diversity were evaluated by metagenomic 454-pyrosequencing of 16S and 18SrRNA genes, respectively. Changes in soil respiration patterns were evaluated by monitoring 12C- and 13C-CO 2 release after soil amendment with 13C-labelled wheat residues. Results show that residue mineralization increased with bacterial richness and diversity in the tilled treatment 7 days after soil amendment. Native soil organic C mineralization and priming effect increased with fungal richness and diversity in improved pasture and natural grassland. No-till cropping systems represented intermediate situations between tillage and pasture systems. Our findings evidence the potential of controlling soil microbial diversity by agricultural practices to improve soil biological properties. We suggest the promotion of no-till systems as a fair compromise between the need for agriculture intensification and soil ecological processes preservation. [ABSTRACT FROM AUTHOR]

Abstract: The conversion of native vegetation (NV) into agricultural land by clearing and tillage disrupts the soil structure, and depletes soil organic carbon (SOC) pool. The data on changes in SOC pools are needed to enhance scientific knowledge regarding the effects of land use and no-till (NT) systems on soil fertility, agronomic productivity, and soil C sink capacity. Thus, the objective of this study was to quantify changes in SOC fractions due to conversion of NV to agricultural land, and to assess the rate of recovery of SOC fractions and the resilience index of NT cropping systems under sub-tropical (Ponta Grossa/PR — PG) and tropical (Lucas do Rio Verde/MT — LRV) regions of Brazil. The conversion from CT to NT was 29 and 8years at the PG and LRV sites, respectively. Five different fractions of SOC pools were extracted by chemical methods (i.e., C in the polysaccharides — CTPS, hot-water extractable C — HWEOC, chemically-stabilized organic C — CSOC), and physical fractionation (i.e., particulate organic C — POC, and mineral-associated organic C — MAOC). Land use change primarily altered the labile (HWEOC, TPS, and POC) and also some of the stable (MAOC) pools at both sites. The CSOC pool was almost constant throughout the soil profile and represented, across land uses, 7.2gCkg−1 at the PG and 3.1gCkg−1 at the LRV sites. At the PG site, the HWEOC and CTPS concentrations in the 0–5cm depth decreased by 56% (1.21gkg−1) and 45% (7.21gkg−1) in CT soil, respectively. At the LRV site, concentrations of HWEOC and CTPS in the 0–5cm depth decreased by 50% (0.4gkg−1) and 42% (4.8gkg−1), respectively. In contrast, concentrations of HWEOC and CTPS fractions in soil under NT in the 0–20cm depth were closer than those under NV, and exhibited a distinct gradient from surface to sub-soil layers. The adoption of CT reduced POC by 46% (4.7Mgha−1), and MAOC by 21% (15.1MgCha−1) in the 0–20cm depth at the PG site. Using CT for 23years at the LRV site, decreased SOC fractions in the 0–20cm depth at the rate of 0.25 and 0.34MgCha−1 yr−1 for POC and MAOC, respectively. In contrast, adoption of intensive NT systems in tropical agro-ecoregions increased POC at the rate of 0.23 to 0.36MgCha−1 yr−1, and MAOC by 0.52 and 0.70MgCha−1 yr−1. An important effect to be emphasized is the possibility of recovering, at least partially, the SOC fractions by adopting high biomass-C inputs under NT management, and despite the fact that the experimental duration at the LRV site was only eight years. With a high and diversified input of biomass-C in intensive NT systems, higher resilience index was observed for CTPS, HWEOC, and MAOC. The variation in SOC among CT and NT systems was mainly attributed to the MAOC fraction, indicating that a significant proportion of that fraction is relatively labile, and that spatial inaccessibility of SOC plays a significant role in the restoration of SOC. [Copyright &y& Elsevier]

Inventories of C and N footprints on a landscape scale are essential tools for estimating C offsets from agricultural emissions. Therefore, the aims of this study conducted in the subtropical humid ecosystem in southern Brazil were to: (i) conduct a soil-specific inventory of landscape soil C and N stocks with reference to soil order, soil texture, and land use/management type; (ii) estimate accretion rates for soil organic C (SOC) and total N (TN) for areas managed under no-till (NT) practices management with reference to native vegetation (NV) based on this inventory; (iii) generate a map of C stocks for each land use system; and (iv) calculate estimated C offset for the region through the use of NT compared to conventional tillage (CT). Soil samples were collected at 324 points to a 1-m depth from the entire region. Soil texture and duration of NT had a strong influence on C and N stocks. The average soil C stock across all types of soils for depths of 0-40 and 40-100 cm was 57.0 and 43.0%, respectively. The extrapolation of C stored in the 0- to 40-cm depth based on the NT management for 11 and 20 yr for 1.52 million hectare (Mha) was 9.08 ± 0.62 Tg (1 Tg = 1012 g) representing 11.9% of the C stored in all soil orders. The long-term of C sink capacity by conversion of arable land from CT to NT in this region is 33.2 Tg of CO2, with the C offset of 22.5% of all anthropogenic emissions. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) pools, particularly labile pools, and soil enzymes are good indicators of short-term impacts of soil management. We hypothesized that labile SOC pools drives C accumulation and enzyme activity can be an efficient indicator for C build up in short-term conservation agriculture. The aims of this study were to quantify the impacts of tillage and crop rotations with diverse crop residue inputs on changes in SOC labile pools and enzymatic activities in rice-, soybean- and cassava-based cropping systems designated as RcCS, SbCS and CsCS, respectively. The four treatments in each cropping system consisted of: conventional tillage (CT), no-till in which main crops (rice, soybean and cassava) were grown in a one-year frequency pattern (NT1) and, no-till in which the main crops were grown in bi-annual rotations with maize (NT2 and NT3). After 5 years experiment period, greater hot-water extractable organic C (HWEO-C) stocks of 61%, 55% and 53%, and permanganate oxidizable C (POX-C) stocks of 23%, 21% and 32% were attributed to NT than those in CT soils under RcCS, SbCS and CsCS, respectively, at 0–5 cm soil layer. The pyrophosphate extractable organic C (PEO-C) and chemically stabilized organic C (CSO-C) stocks were almost constant in each depth among treatments, except 0–5 cm in CsCS. The β-glucosidase activity was 18%, 28% and 49% greater in NT than those in CT soils at 0–5 cm under RcCS, SbCS, CsCS, respectively. Arylsulfatase activity was 36% and 39% greater in NT than in CT under SbCS and CsCS, respectively but no significant differences in RcCS. A strong and positive correlation (P < 0.001) between β-glucosidase and arylsulfatase activity with POX-C, HWE-C, SOC and total N indicated how these variables were inter-related. Comparison among three NT treatments, bi-annual crop rotations showed a better increasing trend of HWEO-C, POX-C and enzymatic activities than those with one-year frequency pattern. In conclusion, short-term NT crop rotations with permanent soil cover significantly increased the storage of HWEO-C and POX-C and enhanced β-glucosidase and arylsulfatase activities at the surface soil layer as a result of higher biomass-C input and the absence of soil disturbance. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays an essential function in global agroecosystems. Conservation agriculture (CA) associated with diverse and high C-input is an important tool to increase SOC, improve soil quality, and increase agronomic productivity. However, the information about the potential of highly weathered soils under CA to accumulate SOC, and when the SOC saturation may occur, is scarce. This study was based on the hypothesis that in highly weathered soil from tropical and subtropical agro-ecosystems, the potential to store SOC lies more in the sub-soil than in surface layers and is determined by nutrient scarcity. Thus, the aim of this study, performed in a long-term incubation experiment (30 months), was to: (i) assess the SOC flow and mineralization based on CO 2 -C emissions for estimating SOC accumulation; (ii) evaluate the impact of nutrient scarcity on C accumulation efficiency by soil layers; and (iii) determine when C saturation occurs in these soils. The incubation study was performed in three Brazilian Oxisols under long-term CA, and was comprised of four amounts of C-inputs (0, 6, 12 and 24 Mg C ha − 1 ) added at 0, 10 and 20-months to three soil layers (0–20, 20–40 and 40–100 cm). The CO 2 -C emission was 19.0, 9.0 and 7.0% higher in the 0–20 cm than that in 40–100 cm layer for Ponta Grossa, Londrina and Lucas do Rio Verde sites, respectively, which was associated with higher antecedent SOC content and fertility status. A higher SOC accumulation efficiency was observed for the 0–20 cm layer than in deeper layers. Nutrient scarcity in deep soil layers; especially that of P, Ca 2 + and Mg 2 + ; was the driving force limiting SOC accumulation. Carbon saturation was not achieved indicating a high SOC storage capacity in these soils. Because these and similar soils cover a large global area, they possess a large C sink to mitigate atmospheric CO 2 -C . The potential SOC storage estimated for 20–100 cm layer based on this study and upscaling for 1/3 Brazilian Oxisols (100 million ha) may offset 0.06 to 0.36 Pg C yr − 1 or 5.5% to 32.7% of the global annual greenhouse gas emissions by land use change. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA) is an effective tool that is used to increase soil C sequestration and enhance soil quality and agronomic productivity. However, rigorous empirical evidence from Southeast Asia, particularly in the Cambodian agro-ecosystem, is still scarce. We hypothesized that high and diversified biomass-C inputs in CA might be the first step toward to increase SOC in the topsoil by creating the C flow to support C storage overtime. Thus, the aim of this study was to quantify the short-term (i.e., five year) impacts of soil management and cropping systems on soil organic C (SOC), soil total N (STN), particulate organic C (POC) and mineral-associated organic C (MAOC). There were three distinct experiments comprised of a combination of cover and main crops including rice-, soybean- and cassava-based cropping systems, hereafter designated as RcCS, SbCS and CsCS, respectively. The experimental plots were laid out in a randomized complete block design with three replicates. Soil management treatments included conventional tillage (CT) and no-till (NT) and a selected adjacent area of reference vegetation (RV). Soil sampling was conducted in 2011 and 2013 at seven depths (0–5, 5–10, 10–20, 20–40, 40–60, 60–80 and 80–100 cm). Soil management and crop sequences significantly affected SOC and STN stocks in all three cropping systems. On average, NT SOC stocks at 0–5 cm depth was greater than those of CT by 10%, 20% and 18% and STN stocks by 8%, 25% and 16% for RcCS, SbCS and CsCS, respectively. SOC levels followed the order RV > NT > CT. SOC stocks in the subsoil layers were consistently lower in NT than in CT in all three cropping systems. POC stocks at 0–5 cm depth in NT were on average 22%, 20% and 78% greater than those in CT in RcCS, SbCS and CsCS, respectively. However, significant differences were detected only in RcCS and CsCS. The major POC stocks were found at 0–20 cm depth. NT treatments in SbCS stored 9% greater MAOC stocks at 0–5 cm depth than those in CT, and an increasing trend of NT was observed in RcCS and CsCS. In all three cropping systems, NT systems with diversified crop species significantly increased SOC stocks ranging by 6 to 28% and POC stocks by 56–127% in the surface soils and tended to restore SOC and POC in the subsoil layers after five years. The results leads to accept the hypothesis that short-term CA associated with high biomass-C inputs (particularly bi-annual rotations) promotes SOC recovery in the topsoil layer and creates a potential to increase SOC in the subsoil layers when deep-rooting cover crops are included in crop rotations. [ABSTRACT FROM AUTHOR]

• A new in-field indicator to assess soil organic carbon (SOC) dynamics is tested. • The indicator is sensitive and robust under various agroecosystems in tropical context. • The trends of SOC dynamics measured are consistent with Rock-Eval indicators. • First characterization of C pools associated to POXC-BSR indicator. The assessment of the impacts of land-use and management on soil organic carbon (SOC) dynamics is a major environmental concern, as the soil carbon cycle underpins key ecosystem services. However, assessments based on short-term SOC dynamics face methodological and experimental difficulties. Hurisso et al. (2016) proposed a method to assess SOC dynamics by coupling two methods: Permanganate Oxidizable Carbon (POXC) and Basal Soil Respiration (BSR). This method has been used in laboratory on dried and re-wetted soil samples from temperate regions mainly. In our study, we adapted this method to the field and proposed a cost-effective in-field indicator combining the POXC and in situ Basal Soil Respiration (SituResp® method). We tested the indicator at four study sites (n = 169 points) within various tropical land-use and management contexts based on rubber, soybean and oil palm cropping systems respectively in Thailand, Cambodia and Indonesia. The results demonstrated the relevance, sensitivity and robustness of the POXC-SituResp® indicator to characterize the impact of a gradient of disturbance on SOC dynamics. The results also highlighted the potential of conservation agriculture (no-tillage and crops residues) and compost amendments to accumulate SOC. Rock-Eval® analysis showed that POXC-SituResp® indicator is negatively linked to excess of potentially mineralizable labile carbon. Carbon pools targeted by the POXC were specified by Rock-Eval® pyrolysis measurements to be a rather thermal resistant pool of SOC. Our study confirms that the integrated indicator based on POXC and BSR assess a relative carbon stabilization of SOC pools. This indicator can be measured in the field by a rapid and cost-effective method. [ABSTRACT FROM AUTHOR]