A dataset for soil organic carbon in agricultural systems for the Southeast Asia region.

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.

Can C-budget of natural capital be restored through conservation agriculture in a tropical and subtropical environment?

Conservation agriculture through no-till based on cropping systems with high biomass-C input, is a strategy to restoring the carbon (C) lost from natural capital by conversion to agricultural land. We hypothesize that cropping systems based on quantity, diversity and frequency of biomass-C input above soil C dynamic equilibrium level can recover the natural capital. The objectives of this study were to: i) assess the C-budget of land use change for two contrasting climatic environments, ii) estimate the C turnover time of the natural capital through no-till cropping systems, and iii) determine the C pathway since soil under native vegetation to no-till cropping systems. In a subtropical and tropical environment, three types of land use were used: a) undisturbed soil under native vegetation as the reference of pristine level; b) degraded soil through continuous tillage; and c) soil under continuous no-till cropping system with high biomass-C input. At the subtropical environment, the soil under continuous tillage caused loss of 25.4 Mg C ha-1 in the 0-40 cm layer over 29 years. Of this, 17 Mg C ha-1 was transferred into the 40-100 cm layers, resulting in the net negative C balance for 0-100 cm layer of 8.4 Mg C ha-1 with an environmental cost of USD 1968 ha-1. The 0.59 Mg C ha-1 yr-1 sequestration rate by no-till cropping system promote the C turnover time (soil and vegetation) of 77 years. For tropical environment, the soil C losses reached 27.0 Mg C ha-1 in the 0-100 cm layer over 8 years, with the environmental cost of USD 6155 ha-1, and the natural capital turnover time through C sequestration rate of 2.15 Mg C ha-1 yr-1 was 49 years. The results indicated that the particulate organic C and mineral associate organic C fractions are the indicators of losses and restoration of C and leading C pathway to recover natural capital through no-till cropping systems.

Macroaggregation and soil organic carbon restoration in a highly weathered Brazilian Oxisol after two decades under no-till.

Conclusions based on studies of the impacts of soil organic carbon (SOC) fractions and soil texture on macroaggregation and SOC stabilization in long-term (>20years) no-till (NT) fields remain debatable. This study was based on the hypothesis that the amount and frequency of biomass-C input associated with NT can be a pathway to formation of macroaggregates and to SOC buildup. The objectives were to: 1) assess the macroaggregate distribution (proportional mass, class mass) and the SOC and particulate organic carbon (POC) stocks of extra-large (8-19mm), large (2-8mm) and small (0.25-2mm) macroaggregate size classes managed for two decades by NT, and 2) assess the recovery of SOC stocks in extra-large macroaggregates compared to adjacent native vegetation (Andropogon sp., Aristida sp., Paspalum sp., and Panicum sp.). The crop rotation systems were: soybean (Glycine max L.), maize (Zea mays L.) and beans (Phaseolus vulgaris L.) in summer; and black oat (Avena strigosa Schreb), white oat (Avena sativa), vetch (Vicia sativa L.), black oat.+vetch (Avena strigosa Schreb+vetch) and wheat (Triticum aestivum L.) in winter. The experimental was laid out as 2×2 randomized block factorial with 12 replicates of a NT experiment established in 1997 on two highly weathered Oxisols. The factors comprised of: (a) two soil textural types: clay loam and sandy clay, and (b) two sampling depths: 0-5 and 5-20cm. The three classes of macroaggregates were obtained by wet sieving, and the SOC content was determined by the dry combustion method. The extra-large macroaggregate classes in 0-20cm depth for sandy clay (SdC) and clay loam (CL) Oxisol represented 75.2 and 72.4% of proportional mass, respectively. The SOC and POC stocks among macroaggregate classes in 0-5 and 5-20cm depths decreased in the order: 8-19mm>2-8mm ≈ 0.25-2mm. The SdC plots under soybean/maize at 3:1 ratio recovered 58.3%, while those at 1:1 ratio (high maize frequency) in CL recovered 73.1% of SOC stock in the extra-large macroaggregates compared with the same under native vegetation for 0-20cm depth. Thus, partial restoration of the SOC stock in original extra-large macroaggregate confirms the hypothesis that NT through higher maize cultivation frequency can be a pathway to fomation of macroaggregates and SOC buildup.