Permanent raised bed planting of the pigeonpea–wheat system on a Typic Ustochrept: Effects on soil fertility, yield, and water and nutrient use efficiencies

In the Indo-Gangetic Plain region, a major deterrent to large scale adoption of the otherwise advantageous pigeonpea–wheat cropping system is the poor crop stand of pigeonpea due to temporary water logging during the rainy (monsoon) season, leading to its low productivity and a smaller residual effect on the succeeding wheat crop. The permanent raised bed (PRB) system of planting, as widely used particularly for wheat in different countries, has seldom been studied in the pigeonpea–wheat system. We, therefore, conducted a field experiment at Modipuram (29°4′N, 77°46′E, 237 m asl), India, for 3 consecutive years (2001–02 to 2003–04) to evaluate the PRB vis-à-vis the conventional flat bed (FB) system of planting at varying fertilizer NP rates in the pigeonpea–wheat system, in terms of changes in soil organic carbon, nutrient and water use efficiencies, annual productivity and economic returns. Pigeonpea grown on PRB had lower plant mortality (4–7%) and higher yield (1.6–2.1 t ha−1) as compared to FB with 26–36% mortality and yield of 1.3–1.8 t ha−1. Pigeonpea on PRB had greater N and P recycling (11–23% N and 8–14% P) through its residue comprising root, stubble and leaf litter. Although wheat yield following pigeonpea under PRB was lower (p < 0.05) compared with that under FB, the system productivity in terms of wheat equivalent yield was 8.44% higher under PRB. The economic optimum doses of fertilizer N and P for wheat in the pigeonpea–wheat system were smaller (128 kg N and 28 kg P ha−1) under PRB as compared to FB (152 kg N and 30 kg P ha−1) owing to increased N and P supply, greater P use efficiency and a better crop growth environment under PRB planting. The N use efficiency indices were significantly greater (p < 0.05) in wheat under FB compared to those under PRB. By contrast, P use efficiency was greater under PRB, particularly in treatments that received both N and P fertilizers. Compared with FB, the root mass density (20–46%) of wheat was also greater under PRB in surface and sub-surface soil layers. PRB favored saving of irrigation water by 9.5–13.4 ha cm and improved the irrigation application efficiency by 9.5–13.4% and the irrigation use efficiency by 19–28 kg ha cm−1 over FB. The post-wheat harvest nitrate N (NO3-N) at 20–40 cm soil depth in plots fertilized with 120 or 180 kg N ha−1 was greater under FB planting (10.25–13.81 mg kg−1) compared to PRB (7.33–8.42 mg kg−1), suggesting that PRB planting might reduce NO3-N leaching to deeper soil layers. Similarly, in the treatments that received both N and P, NO3-N in soil below 20 cm depth was lower compared to those receiving N or P alone. After three crop cycles, soil OC and the Olsen-P content in the 0–20 cm depth were increased compared to the initial content under both planting techniques but the magnitude of increase was greater under PRB. Compared with FB, the annual net returns of the pigeonpea–wheat system were greater by US$ 210 ha−1 under PRB, and the crop also required less specific energy (1.99 MJ kg−1) compared with the FB planting (3.18 MJ kg−1).