In-season nitrogen management strategy for winter wheat: Maximizing yields, minimizing environmental impact in an over-fertilization context

Applying only as much N fertilizer as is needed by a crop has agronomic and environmental benefits. On-farm experiments were conducted at nine sites in the North China Plain (NCP) to evaluate agronomic performance and potential environmental impacts of an in-season N management strategy (INM) for winter wheat (Triticum aestivum L.). According to INM, optimal N rate (ONR) was determined using soil nitrate-N tests in the root zone and N target values for two periods of wheat growth (before or after stem elongation stage). Across all the nine sites, the ONR ranged from 71 to 170 kg N ha−1 with a mean of 126 kg N ha−1, which was closely correlated with economically optimal N rate (EONR; EONR = 1.06 × ONR, r = 0.97), the latter derived from yield response curves. Grain yields at ONR, ranging from 5.6 to 7.4 t ha−1 with a mean of 6.5 t ha−1, equaled maximum yield based on yield response curves. Adding more N beyond ONR did not increase yield but increased residual soil nitrate-N after harvest from 99 to 115 kg ha−1 and estimated N losses from 29 to 40 kg ha−1 at 130% ONR. The treatment mimicking typical N rates of local farmers exhibited the greatest N loss potential (residual soil nitrate-N of 228 kg ha−1 and N loss of 133 kg ha−1 on average). Treatments below ONR led to a 9% yield reduction at 70% ONR, compared to ONR treatment. In conclusion, the ONR using the INM can maximize grain yield while minimizing environmental impact of N fertilization by integrating the utilization of indigenous N sources and match N supply to crop requirements.