Evaluation of water and nitrogen use efficiencies in a double cropping system under different integrated management practices based on a model approach

Irrigation, fertilization, and cultivation managements play important roles in crop production in the North China Plain (NCP). This study aims to compare crop yields, and water and N use efficiencies (WUE and NUE) in a wheat-maize cropping system under different integrated management practices and recommend the best management practices (BMPs). A two-year experiment involving four integrated management practices was conducted in Tai'an City, Shandong Province in the NCP. These management practices were designed as follows: (1) traditional farming practice (FP); (2) optimized combination of cropping and fertilization (OPT-1); (3) practice for high yield (HY), which does not consider the cost of resource inputs to maximize grain yield; and (4) further optimized combination of cropping and fertilization (OPT-2), which is based on the HY practice. Soil water movement, nitrate transport, and crop growth were all simulated using the soil water, heat, carbon, and N simulation (WHCNS) model. Results indicated that simulated soil water content and nitrate concentration at different depths in soil profiles, leaf area index, dry matter weight, and grain yield were all in good agreement with the field-measured data. Simulation results indicated that the amounts and dates of irrigation and fertilization, planting method, planting density, and sowing date had obvious effects on grain yield, water drainage, total N loss, WUE, and NUE. The annual average total N loss under the OPT-1 practice decreased by about 28.6% compared with the FP practice, whereas the annual average grain yield and NUE increased by 27.7% and 25.7%, respectively. The largest annual average grain yield and total N loss occurred in the HY practice (23,590 kg ha−1 and 240.6 kg N ha−1, respectively). Although the annual average grain yield of the OPT-2 practice was 15.4% lower than that of HY practice, the NUE was 19.2% higher in OPT-2 than in HY. The annual average nitrate leaching under the OPT-2 practice was the lowest and reached 25.5%-60.0% compared with those under other practices. Among the four practices, the OPT-2 practice achieved the most preferable results; the lowest N loss and the highest NUE were obtained at the expense of a slight decrease in grain yield. Therefore, the OPT-2 practice was the BMPs among the four practices and should be recommended to maximize the economic and environmental benefits in the study region.