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Soil conservation and carbon sequestration are critical issues in the Indian Himalayas. This study, conducted from 2005 through 2009 on a sandy clay loam soil near Almora, India, with two tillage (conventional tillage [CT] and zero tillage [ZT]) and five fertilization management practices (100% NPK [F1], 50% NPK + 10 Mg farmyard manure [FYM] ha j1 [F2], 50% NPK + 10 Mg poultry manure [PM] ha j1 applied on equivalent N basis of 10 Mg FYM ha j1 [F3], 100% NPK + 10 Mg FYM ha j1 [F4], and 100% NPK + 10 Mg PM ha j1 applied on equivalent N basis of 10 Mg FYM ha j1 [F5]). The effects of these practices on soil organic carbon (SOC) retention and its physical and chemical pools, soil aggregation, and aggregate-associated C contents in the 0-to 15-cm soil layer were evaluated. The plots under ZT had nearly 11% and 12% higher total SOC and particulate organic matterYC (POM-C) concentrations, respectively, compared with CT (È12 and 4 g kg j1 soil, in that order) plots in the 0-to 5-cm soil layer. Plots under F4 and F5 had significantly higher total SOC and POM-C contents than F2-and F3-treated plots in both soil layers. Although the labile pools of SOC were positively affected by ZT and fertilization, the recalcitrant pool was not. Plots under ZT had higher macroaggregates, mean weight diameter (MWD), and macroaggregate-associated SOC compared with CT in the surface soil layer only. Similarly, F4-or F5-treated plots had higher macroaggregates, MWD, and macroaggregate-associated SOC compared with F1-, F2-, or F3-treated plots in that layer. All C pools had significant positive relationship with the MWD (in millimeters) in the 0-to 5-cm soil layer (n = 40), except for the nonlabile pool. However, only very labile (Pool I) and labile (Pool II) C pools had significant relationships with the proportion of macroaggregates in the 0-to 5-cm soil layer. Thus, adoption of year-round ZT along with 100% NPK in rice and 100% NPK + FYM/PM addition in wheat is the best management option under an irrigated rice-wheat system in the Indian Himalayas, as the management practice has the potential to maintain productivity and improve soil aggregation with greater accumulation of POM-C and SOC stabilization.

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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.