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 NO3-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 ON 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 NO3-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 NO3-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.