Soil water and nitrogen interaction effect on residual soil nitrate and crop nitrogen recovery under maize–wheat cropping system in the semi-arid region of northern India

Over fertilization of nitrogen (N) in the premise of higher crop yield has sometimes led to build up of residual soil nitrate and pollution of ground water. Though, maize and wheat are two heavy feeders of N, studies on soil nitrate dynamics under maize–wheat cropping system in the Indo-Gangetic Plains of northern India, are limited. Hence, the present study was carried out at the research farm of Indian Agricultural Research Institute, New Delhi with maize–wheat cropping sequence grown for four consecutive cropping seasons, during 2002–2004. The treatments consisted of three levels of water regimes and five N levels taken in split plot design. Three levels of water regime, namely, W1, W2 and W3 referred to as limited, medium and maximum number of recommended irrigation. The five N levels were T1 (0% N), T2 (75% N), T3 (100% N), T4 (150% N) and T5 (100% N from organic source). For both the crops, 100% N corresponded to the recommended dose of 120 kg N ha−1 from inorganic source. Irrespective of crop, N recovery was higher under T2 and W3 treatment combination, though yield and biomass were highest under T4 and W3 treatments. Nitrogen recovery from organic treatment gradually increased from 8.8% in the first crop season (maize, 2002) to 26.1% in the last crop season of the experiment (wheat, 2004). Peak NO3− concentration was observed at 15–30 cm soil depth in W1 and W2 treatments and at 30–60 cm in W3 water regime. The NO3− buildup was higher in W1 as compared to W3 treatment and was to the extent of 62 kg ha−1 in the 0–120 cm soil profile under W1T4 treatment after four crop seasons. Across water treatments, soil NO3− was higher under T4 (150% N), followed by T3 (100% N) throughout the experiment period. Despite a trend of soil NO3− buildup, application of N (150%) maximized crop productivity (maize and wheat) under W3. The study revealed that maize–wheat cropping system grown under higher N application levels beyond the recommended dose, would reduce N use efficiency and enhance soil nitrate buildup.