Yields and Nitrogen Dynamics in a Rice–Wheat System Using Green Manure and Inorganic Fertilizer

Abstract

Integrating fertilizer N (FN) with legume green manures (GM) can foster sustainable and environmentally sound agricultural systems in subtropical, semiarid soils low in organic matter. A 4‐yr replicated field experiment with irrigated rice (Oryza sativa L.) and wheat (Triticum aestivum L.) rotations was conducted on a sandy loam soil in the Punjab of India to evaluate the effects of incorporating cowpea (Vigna unguiculata L.) or sesbania (Sesbania aculeata L.) GM on crop productivity, N‐use efficiency, and NO3 leaching. Rice grain yields with pretransplant incorporation of 20 and 40 Mg GM ha−1 (GM20 and GM40) ranged from 5.18 to 5.81 Mg ha−1, which were equivalent to the 5.40 Mg ha−1 obtained with 120 kg FN ha−1 (FN120). Rice yield with 60 kg FN ha−1 (FN60) and GM20 was double the control yield and 6% greater than the FN120 treatment. Nitrogen utilization by rice was greater for GM20 than FN, as indicated by greater fertilizer N equivalents and an apparent N recovery by rice of 79 vs. 63%. While FN had no residual effects, residual GM produced greater wheat yields, indicating that FN applied to wheat could be reduced by 25%. Soil NO3–N leaching to 60 cm in the rice crop was apparently used by the subsequent wheat crop, which has a deeper and more extensive rooting system. After 4 yr, use of FN120 for both crops resulted in 35 kg of residual NO3–N ha−1 in the 150‐cm soil profile (74% below 90 cm), whereas only 19 kg NO3–N ha−1 remained with GM20 plus FN60. Use of GM20 with FN60 for a rice–wheat rotation demonstrated greater yields of rice and wheat, 25 to 50% reduction in fertilizer N use, and decreased potential for groundwater NO3 contamination.