The assessment of nitrate leaching in a rice–wheat rotation system using an improved agronomic practice aimed to increase rice crop yields

Abstract

To increase the rice yield and nitrogen (N) use efficiency (NUE), an integrated agronomic practice, including rapeseed cake addition, increased fertilizer frequency, improved irrigation and crop cultivation management, was adopted in the Taihu Lake region of China. The environmental impacts of the whole rice–wheat rotation system have not yet been fully evaluated. Here, a two-rotation field trail system was used to assess the effects of the improved practice adopted in rice season on crop yield and nitrate (NO3−-N) leaching in the rice–wheat rotation. Four treatment conditions were used—control (CK), conventional (CT), reduced N (RT), and improved (IP). During the rice season, the leaching losses of NO3−-N in the IP treatment group (2.29–3.88kgNha−1) were lower than those in the CT treatment group (4.11–5.38kgNha−1), and the former had a 28.55% higher crop yield than the latter. Similarly, the RT treatment had lower N leaching loss and a 9.32% higher rice crop yield than the CT treatment. In the wheat seasons, the CT treatment had 41.83% and 38.03% higher NO3−-N leaching than the RT and IP treatments, respectively, despite the three treatments having the same fertilizer application and field management; and N leaching was strongly affected by chemical N surplus in rice season. The RT treatment had the lowest wheat yield, which was 18.72% and 32.06% lower than the CT and IP treatments, respectively; and wheat yield appeared an exponentially increasing response to N surplus that included organic fertilizer N from rice production. These results indicated that management practices applied in rice season had subsequent effect on N leaching and crop yield of the following wheat season. During the whole rice–wheat rotation system, the IP treatment produced 23.56% higher crop yield and 30.87% lower TN leaching than the CT treatment. The IP treatment also increased chemical NUE by 24.67–31.22% and agronomic efficiency of applied chemical N (AEN) by 17.71–33.4% compared with the CT and RT treatments. Thus, compared with traditional practice and reduced N use management, the improved practice management was more in line with the target of food increase and environmental protection.