Tillage and Irrigation Effects on Soil Aggregation and Carbon Pools in the Indian Sub‐Himalayas.

Carbon retention is a critical issue in arable farming of the Indian Himalayas. This study, conducted from 2001 through 2010 on a sandy clay loam soil, evaluated the effect of tillage alterations (conventional tillage [CT] and zero tillage [ZT]) and selected irrigation treatments (I1: pre‐sowing, I2: pre‐sowing + active tillering or crown root initiation, I3: pre‐sowing + active tillering or crown root initiation + panicle initiation or flowering, and I4: pre‐sowing + active tillering or crown root initiation + panicle initiation or flowering + grain filling), applied at the critical growth stages to rice (Oryza sativa L.) and wheat (Triticum aestivum L.) on soil organic C (SOC) retention and its pools, soil aggregation, and aggregate‐associated C contents in the 0‐ to 30‐cm soil layer. Results indicate that the plots under ZT had nearly 17 and 14% higher total SOC and particulate organic C contents compared with CT (∼9.8 and 3.6 g kg−1 soil) in the 0‐ to 5‐cm soil layer after 9 yr of cropping, despite similar mean aboveground biomass yields of both crops on both CT and ZT plots. Tillage had no effect on C pools in the subsurface layers. Irrigation had positive impact on SOC content in the 0‐ to 5‐ and 5‐ to 15‐cm layers. Although the labile pools of SOC were positively affected by ZT, the recalcitrant pool was not. Plots under ZT and I4 also had higher large and small macroaggregates and macroaggregate‐associated SOC. Thus, adoption of ZT is the better management option for soil C improvement than CT, and irrigation generally enhances the positive impacts. [ABSTRACT FROM AUTHOR]