Optimal management of water and nitrogen for farmland in North China Plain based on osculating value method and WHCNS model

Abstract: Optimizing water and nitrogen (N) management is important for high grain yield, resource-efficient and environment-friendly targets in North China Plain (NCP). In this study, the Soil Water Heat Carbon and Nitrogen Simulation (WHCNS) model was combined with the osculating value method to achieve this objective. A 2-year experiment involving 4 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 did not consider the cost of resource inputs to maximize grain yield; and 4) further optimized combination of cropping and fertilization (OPT-2), which was based on the HY practice. The dynamics of soil water content and soil nitrate concentration in different soil depths were monitored, crop dry matter and leaf area index at the key crop growth stages and yield were measured. These dataset was used to test the WHCNS model. After calibration and validation, the scenario analysis was conducted by the validated WHCNS model, which included 165 scenarios of winter wheat and 55 scenarios of summer maize with different water and N management combinations. The osculating value method was then employed to obtain the best management practices (BMPs). This method took into account agronomic, environmental and economic benefits. The results showed that the winter wheat yield increased firstly with the amount of irrigation and then kept steady when reached the maximum. There was no significant relationship between maize yields with irrigation due to the summer maize growth was synchronized with rains in NCP. The yield of winter wheat and summer maize increased with the amount of fertilizer firstly, and then remained stable when reached the maximum. The amount of water drainage and nitrogen leaching increased significantly with the irrigation amount and fertilizer application rates. The optimal irrigation amount and fertilization rates were 240 mm and 60 kg/hm2 (based on N) for winter wheat, respectively. The fertilizer-N application at a rate of 90 kg/hm2 with no irrigation was the BMPs for summer maize. Of all the scenarios, the BMPs could guarantee 97% of the maximum annual yield, higher water and N use efficiency and the highest value-cost ratio (VCR), whilst N leaching and gas loss reduced by 77% and 71%, respectively. Thus, this method can be used to optimize management of water and nitrogen in farmland effectively.