Irrigation combines with nitrogen application to optimize soil carbon and nitrogen, increase maize yield, and nitrogen use efficiency

Staged water shortages and excessive nitrogen application lead to a decline in crop yield, and nitrogen loss, waste of resources and environmental pollution. In order to explore the appropriate water management in humid areas and to determine an efficient nitrogen rates for maize, we conducted the two years’ field experiment.

We conducted a field experiment (2020–2021), with five nitrogen rates N0, N150, N200, N250, N300 (0, 150, 200, 250, 300 kg ha⁻¹) under different water conditions (rainfed conditions and irrigated conditions).

Consequently, under the irrigated conditions, the soil organic matter (SOM), microbial biomass carbon (MBC), dry matter accumulation and grain yield were significantly (P < 0.05) increased by 8.06%, 15.50%, 11.43% and 13.86%, respectively, compared with the rainfed conditions. And the total nitrogen (TN), nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N) decreased significantly by 4.38%, 8.28%, 13.21%, respectively. Furthermore, compared with other nitrogen rates, N250 and N300 combined with irrigated conditions significantly (P < 0.05) increased soil carbon and nitrogen content, dry matter accumulation and grain yield. However, N250 and N300 displayed no significant difference (P > 0.05) in TN, NO₃⁻-N, NH₄⁺-N, SOM, MBC, dry matter accumulation and grain yield. Moreover, under the irrigated conditions, when the nitrogen rates increased more than 250 kg ha⁻¹, the nitrogen use efficiency decreased.

Application of nitrogen rates of 250 kg ha⁻¹ under irrigated conditions is the best choice to increase grain yield, improve nitrogen use efficiency, and ensure safe and efficient production in maize.