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

Abstract

Carbon retention is a critical issue in arable farming of the Indian Himalayas. Th is study, conducted from 2001 through 2010 on a sandy clay loam soil, evaluated the eff ect 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 fl owering, and I4: pre-sowing + active tillering or crown root initiation + panicle initiation or fl owering + grain fi lling), 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 aft er 9 yr of cropping, despite similar mean aboveground biomass yields of both crops on both CT and ZT plots. Tillage had no eff ect 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 aff ected by ZT, the recalcitrant pool was not. Plots under ZT and I4 also had higher large and small macroaggregates and macroaggregate-associated SOC. Th us, adoption of ZT is the better management option for soil C improvement than CT, and irrigation generally enhances the positive impacts.