One-time root-zone N fertilization increases maize yield, NUE and reduces soil N losses in lime concretion black soil

Excess N-fertilizer application and inappropriate fertilization methods have led to low N use efficiency (NUE) and high N leaching. A field experiment was performed in a typical lime concretion black soil area to compare N application methods: split surface broadcasting (SSB) and one-time root-zone fertilization (RZF) on grain yield, NUE, the fate of ¹⁵N urea and soil N loss during the 2015 and 2016 maize growing seasons. Each application method was tested at N rates of 135 and 180 kg N ha^-1, and a control (CK) with no N fertilizer. The RZF treatment remarkably increased grain yield by 7.0% compared with SSB treatment under 180 kg N ha^-1, and significantly increased N derived from fertilizer by 28.5%. The residual ¹⁵N in the 0-80 cm soil layer was 40.6-47.6% after harvest, 61.8-70.9% of which was retained in 0-20 cm. The RZF remarkably increased the ¹⁵N recovery in maize by 28.7%, while significantly decreased the potential N losses by 30.2% compared with SSB in both seasons. In conclusion, one-time RZF of urea is recommended for obtaining high yields, increasing NUE, and minimizing N losses in maize, which deserves more attention for developing and applying in the future.