Optimizing Soil Nitrogen Supply in the Root Zone to Improve Maize Management

Developing agronomically sound, environmentally appropriate N management strategies are critical for the sustainability of agricultural production. Our objective was to evaluate agronomic performance and potential environmental impacts of in‐season N management (INM) against increased or reduced N fertilization on a calcareous alluvial soil for maize ( Zea mays L.) in China. Optimal N rates (ONR) were determined for INM by deducting measured soil NO 3 –N content in root layers from the N target value during three maize growth periods: from planting to three‐leaf stage, three‐ to 10‐leaf stage, and 10‐leaf stage to harvest. Other treatments included a 0 N control, below ONR (70% ONR, 50% ONR, or ONR − 30 kg N ha −1 ), above ONR (130% ONR, 150% ONR, or ONR + 30 kg N ha −1 ), and farmers' N practice (FNP). Across all 14 sites from 2003 to 2006, when N treatment was less than ONR (average 141 kg N ha −1 ), grain yield was significantly reduced from 8.5 to 7.7 Mg ha −1 while maintaining similar residual soil NO 3 –N content and N losses. When extra N fertilizer was applied, no yield gain was achieved, but N losses were significantly increased from 50 to 81 kg N ha −1 The FNP treatment had the lowest N recovery (22%) and greatest residual soil NO 3 –N of 158 kg ha −1 and N loss of 87 kg ha −1 The INM is an extremely practical strategy for effectively utilizing soil N supply, synchronizing N demand and N supply, and addressing site‐specific N management needs.