Minimal soil disturbance and increased residue retention increase soil carbon in rice-based cropping systems on the Eastern Gangetic Plain

The adoption of conservation agriculture (CA) in the intensive triple-cropping, rice-based systems of the Eastern Gangetic Plain (EGP) alters the dynamics of carbon (C) in the soil, but the nature of these changes is poorly understood. Our aim was to determine whether CA in these systems involving non-puddled transplanting of wetland rice and strip planting of dryland crops plus increased residue retention would increase the C storage in soils relative to conventional crop establishment practices. Long-term field experiments were studied in two locations of northwestern Bangladesh to determine C turnover as well as examining C cycling under three levels of soil disturbance (conventional tillage (CT), strip planting (SP) and bed planting (BP)) in combination with low residue (straw) retention (LR, the current practice) and increased residue retention (HR) in Calcareous Brown Floodplain soil (Alipur) and Grey Terrace soil (Digram). The total nitrogen (N), organic C, microbial biomass C (MBC) and water-soluble C (WSC) values were measured in soil samples from 0 to 10 cm depth collected at different stages during the growth of the 13th and 14th crops at Alipur and the 12th and 13th crops at Digram since the treatments commenced. At each location, SP and BP with either LR or HR retained more soil organic C (0–10 cm) from C inputs than CT with HR and LR. In general, the CO2 emissions relative to the stored soil organic C in the soils (0–10 cm) under SP with LR and HR were approximately 13 to 59% lower than those under CT and BP with LR and HR. The higher levels of C mineralization were associated with higher WSC contents in the soil. In contrast, the MBC contents in the HR treatments followed the order SPHR > BPHR > CTHR. Similarly, in SPLR and SPHR, the potentially mineralizable C (PMC) was higher, while the decay rate constant was lower. Increased residue retention with minimal soil disturbance practices (SP and non-puddled transplanting) after 14 crops at Alipur and 13 crops at Digram modified the C cycle by decreasing C emissions and increasing the levels of total organic C in the soil. The application of both minimal soil disturbance and increased residue retention enhanced soil organic C (0–10 cm) concentrations in the two soils under intensive rice-based cropping systems on the EGP.