How Can Urea-N One-Time Management Achieve High Yield and High NUE for Rainfed and Irrigated Maize?

Split nitrogen (N) management is a primary strategy for reducing N loss using the conventional broadcasting method in high-yield maize systems, while increasing labour costs with the progression of labour transfer. This study examined whether localized, one-time urea-N fertilization can achieve high yield for rainfed and irrigated maize in the Huang-Huai-Hai Plain, China. We first identified the critical N placement depth (120 mm) that ensures a high yield and N uptake for the two types of maize in a field experiment. A 2-year field experiment was conducted to validate the root zone one-time N management (RON) strategy based on an optimal placement with seven N levels compared with split N management (SN). With urea point placement, the N movement distance (about 70 mm) was highly limited by the fertilizer placement. The RON consistently maintained a higher soil-available N content than the SN, which stimulated root proliferation and enlarged root surface area, especially for rainfed maize. Hence, the RON, based on placement regulation, increased the yield plateau by 8% while reducing the optimal N rate by 22% for rainfed maize compared with the SN and archived a similar yield plateau while decreasing the optimal N rate by 25% for irrigated maize. Compared with SN, the apparent recovery efficiency of N under the RON treatment increased from 41 to 48%, and from 43 to 54% for irrigated and rainfed maize, respectively. In conclusion, one-time urea-N fertilization based on placement regulation could be an efficient nutrient management strategy for intensive maize systems.