Effects of tillage practices and nitrogen application on maize nitrogen utilization and soil bacterial communities

Grain production in the Huang-Huai-Hai region of China has long relied on high-intensity nitrogen (N) fertilization, resulting in a decoupling between fertilizer input and yield gains as well as conspicuously low nitrogen use efficiency (NUE). To develop a synergistic optimization regime integrating tillage and nitrogen management for reducing N input while enhancing NUE, a field experiment was conducted based on a long-term positioning trial initiated in 2005. The experiment employed two tillage practices (rotary tillage, RT; subsoiling, ST) and three N application rates (100%, 75% and 0% of the conventional dosage). Results showed that ST significantly increased contents of total nitrogen, nitrate nitrogen and microbial biomass nitrogen in the 0–20 cm (p<0.05), while N application elevated soil nitrogen storage in the 0–40 cm profile (p<0.05). Bacterial community diversity and richness peaked under the 75% N treatment but were minimized under 100% N application. Higher N input promoted nitrogen accumulation in maize across all growth stages and increased the proportion of nitrogen allocated to grains. Compared with 100% N, 75% N application improved partial factor productivity of nitrogen, NUE and agronomic nitrogen efficiency. At the same N rate, ST outperformed RT in grain nitrogen accumulation, partial factor productivity of nitrogen and nitrogen harvest index. The conventional N application (100% N) sustained high yields, it compromised NUE. The combined practice of subsoiling and reduced N application can synchronously improve soil quality, crop yield and NUE, providing a feasible technical solution for sustainable grain production in the Huang-Huai-Hai region.