Nitrogen losses trade-offs through layered fertilization to improve nitrogen nutrition status and net economic benefit in wheat-maize rotation system

A unilateral increase in the nitrogen (N) fertilizer application depth reduces gaseous N losses in agricultural systems, however, it elevates N leaching risk. Research addressing how to better balance and optimize N emissions and leaching losses under deep placement fertilization measures remains notably limited. This study attempted to optimize the spatial distribution of N fertilizer in different soil layers to reduce total N losses and further enhance crop productivity. A two-year winter wheat-summer maize rotation experiment was conducted in the Loess Plateau during 2021-2022 and 2022-2023, and a quantitative N balance calculation framework was used to precisely estimate the variations in N losses and N surplus resulting from different single-deep fertilization (CU8, CU16, and CU24, N fertilizer was single placed in the 8, 16, and 24 cm soil layer) and layered fertilization treatments (CU2-1-1, CU1-2-1, and CU1-1-2, N fertilizer placed in the 8, 16, and 24 cm soil layer according to different proportions). The results indicated that, in comparison to the single-deep fertilization, the layered fertilization treatments increased winter wheat and summer maize yields by 4.4-21.3 % and 11.4-21.8 % (P < 0.05), N use efficiency (NUE) increased by 11.1-67.9 % and 32.3-71.0 % (P < 0.05), respectively. The single-deep fertilization struggles to meet the early growth nutrient requirements of winter wheat and summer maize (NNI < 0.95), in contrast, layered fertilization maintained optimal N nutrition status across all growth stages in wheat and maize (1.05 > NNI > 0.95); Singular increase in N fertilizer application depth reduced gaseous N losses significantly while raising N leaching risk, however, the corresponding total N losses (sum of N2O emissions, NH3 volatilization, and N leaching) did not decrease; Specifically, compared with single-deep fertilization, total N loss and N surplus of layered fertilization were reduced by 15.5-37.1 % and 12.2-22.2 %, and the net economic benefits (NEB) were increased by 7.1-33.0 % (P < 0.05). Consequently, layered fertilization further optimizes the single deep fertilization measure in terms of crop production and environmental conservation, and represents an environmentally friendly and economical N fertilization practice.