Yields and nutrient use-efficiency in groundnut-sunflower cropping system in punjab, India

Long-term continuous cereal cropping systems without returning crop residues to soil has led to depletion of inherent soil fertility in semiarid subtropical soils of South Asia. The inclusion of legumes and their residues assumes great significance to restore sustainability. Groundnut (Arachis hypogaea L.) and sunflower (Helianthus annus L.) are important oilseed crops of the region and have the feasibility to be grown in annual double crop rotation with the expansion of irrigation facilities. A 4-year field experiment with irrigated groundnut-sunflower rotation was conducted on a loamy sand soil (Typic Haplustept) to evaluate the effects of different rates of fertilizer N (0, 30 and 60 kg N ha(-1)) and P (0, 20, 30 and 40 kg P2O5 ha(-1) corresponding to 0, 8.7, 13 and 17.5 kg P ha(-1), respectively), applied either to one crop (direct for current crop and residual for succeeding crop) or to both crops (cumulative) each year, with or without 4 t ha(-1) of groundnut crop residues (CR) on crop yields, nutrient uptake, fertilizer use efficiency and soil productivity parameters (pH, organic carbon, available N and P). The residual effects of P and CR were assessed on the succeeding groundnut crop. Winter-grown sunflower responded significantly and consistently to applied fertilizer N and P. Seed yield of sunflower increased significantly up to 60 kg N and 30 kg P2O5 ha(-1) and there was no further increase with directly applied 40 kg P2O5 ha(-1). Cumulative application of P produced sunflower yields comparable with those from direct applications. Incorporation of groundnut residue in conjunction with 30 kg N ha(-1) significantly increased the sunflower yields that were statistically at par with those obtained with the lone application of 60 kg N ha(-1) All through 4 years, the combined application of CR with 60 kg N ha(-1) and 30 kg P2O5 ha(-1) further improved the yield potential of sunflower by 10- 11% and of succeeding groundnut by 10-24%, illustrating the benefit that fertilizer N and P could not achieve. Residual fertilizer P (30 kg P2O5 ha(-1)) produced optimum yields of groundnut, which were comparable with that from directly applied 20 kg P2O5 ha(-1). After 4 years of study, soil organic carbon swelled by 22% and Olsen-P increased from initial 12 kg P ha(-1) to 24-43 kg P ha(-1) in fertilizer and CR-treated plots. These results illustrated that in groundnut-sunflower rotation, (1) 60 kg N and 30 kg P2O5 ha(-1) are adequate for the sustaining optimal sunflower production; (2) whereas the application of fertilizer P to sunflower crop is required, P requirement of groundnut can be met from soil-derived and residual fertilizer P; and (3) incorporation of groundnut crop residues in conjunction with the adequate rates of N and P has complementary effects in maximizing the yields, uptake of N and P, and nutrient use-efficiency in sunflower as well as its residual effects on succeeding groundnut crop, and in sustaining long-term soil productivity.