Soil organic carbon sequestration and modeling under conservation tillage and cropping systems in a rainfed agriculture

Conservation agriculture is a well-established method for promoting carbon sequestration and reducing greenhouse gas emissions, but little is known about how it affects subtropical dryland farming systems. The goal of this study was to evaluate the potential of conservation agriculture in Pakistan's subtropical dryland to reduce atmospheric CO2 enrichment and alter soil organic carbon fractions. In a field experiment, fallow-wheat (farmers' practice) and the conservation tillage methods minimum tillage (MT), reduced tillage (RT), and zero tillage (ZT) were compared to conventional tillage (CT) in the main plots and the cropping systems sorghum-wheat (S-W) and mungbean-wheat (M-W) to fallow-wheat (F-W) in the sub-plots. Multiple assessments taken over a two-year period revealed that CT plots lacked greater soil organic carbon and its fractions than ZT and RT plots. In comparison to CT, ZT, and RT exhibited higher average total organic carbon (TOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) concentrations, respectively, of 1.43% and 1.31%, 4.61% and 2.83%, 2.42% and 1.97%, and 1.66% and 1.76%. In comparison to the S-W cropping system, the F-W and M-W cropping systems showed increased MBC and MOC, but POC and TOC were little impacted. The maximum TOC (0.589% and 0.589%), MBC (0.021% and 0.021%), POC (0.195% and 0.192%), and MOC (0.489% and 0.485%) were found in the combinations of ZT with F-W and M-W. Regardless of the cropping systems, cumulative CO2 flow was lowest in ZT plots compared to the other tillage techniques. The CENTURY model confirmed that the use of continuous tillage is a major threat to both soil fertility and production. The study, therefore, concludes that ZT and RT systems in particular are potential possibilities for carbon sequestration in subtropical dryland soils for CO2 reduction.