Crop production and nutrient use efficiency of conservation agriculture for soybean–wheat rotation in the Indo-Gangetic Plains of Northwestern India

Continuing cereal-based crop rotations such as rice–wheat, intensive cultivation and complete removal of postharvest crop residue (CR) for animal consumption and fuel, or its burning have reduced the organic matter content and productivity of irrigated semi-arid subtropical soils of South Asia. Identification of effective strategies for the management of tillage and CR could foster sustainable and environmentally sound agricultural systems. To this effect, a 4-year field experiment was established with annual soybean–wheat rotation under subtropical climate conditions in the Indo-Gangetic Plains of Northwestern India to evaluate the integrated effects of tillage, CR retainment, mineral fertilizers and farmyard manure (FYM) on crop production, nutrients uptake, soil moisture storage and temperature dynamics. The experimental soil was loamy sand, poor in organic C and low in available P. Sixteen treatment combinations involved recommended and 25% higher NP rates without or with 10tFYMha⁻¹ and CR incorporated in conventional tillage (CT) and retained on the soil surface in conservation agriculture (CA) system. The results clearly revealed that (a) soybean yield was 2–6% higher in CA than CT in different treatments with and without CR, (b) significantly higher uptake of N and P by soybean from CR-amended treatments of both CT and CA, which reflected its effect in improving the soybean yield, (c) the current fertilizer NP recommendation of 20kgN and 26kgPha⁻¹ for soybean is not adequate and either application of 25% higher NP rate (25kgN and 33kgPha⁻¹) or additional 10tFYMha⁻¹ is required for optimum crop production of ∼2500kgha⁻¹, (d) CA conserved more water in soil profile than CT, however, the differences in soil moisture storage in CT vis-à-vis CA were not reflected in soybean yield presumably due to frequent wetting of soil by heavy monsoonal rains, (e) the wheat yield was highest in both CT and CA systems when grown with the application of 150kgN and 33kgPha⁻¹ without CR and was 7% higher in CA (4140kgha⁻¹) than CT (4048kgha⁻¹), and (f) retention of CR on soil surface in winter-grown wheat under CA reduced wheat yield by 8–24% and N uptake by 3–5% as a consequence of mulching effects creating cooler environment in surface soil layer during initial 3 weeks after seeding, which led to the delayed germination and relatively poor crop growth during initial period.