Scientific field management is an important path to realize ecological production and sustainable development of agriculture. As the main content of field management, nitrogen (N) management is the key to balance the economic and ecological benefits of agricultural production. In the loess hilly-gully region, for the fragile ecological and social system, ecologicalization of agricultural production is an important direction to promote sustainable agricultural development. However, irrational fertilization has been one of the main constraint factors, hindering the ecologicalization of local agriculture. In order to solve the problem and prove the practical significance of field management to ecologicalization of agriculture, this study aimed at evaluating the effects of different N fertilization rates and timing using Root Zone Water Quality Model (RZWQM) and then optimizing the N management. Experiments were conducted from 2018 to 2019 in Yangjuangou watershed, loess hilly-gully region, to calibrate and validate the model. The root mean square error (RMSE) of soil water content, nitrate N concentration, above-ground biomass, leaf area index ranged from 10.5-13.5 mm, 2.96-3.80 mg·kg1, 730.3-1273.9 kg·ha1 and 0.26-0.38, respectively, with the agreement index (d) between observed and simulated values ranging between 0.88 to 0.98. Simulation results showed that N leaching in semi-arid areas was also quite high due to concentrated rainfall and loose soil, which had previously been neglected. When the fertilization rate decreased by 35% (applying the chemical fertilizer at rate of 245.7 kg N ha1) of typical fertilization (applying the chemical fertilizer at rate of 378.0 kg N ha1), the leaching and residual N decreased by 72.2%-75.4% and 35.6%-50.9%, respectively, while NUE increased by 41.5%-45.2% with no reduction in maize yield. Additionally, compared with applying additional N at seedling stage in one batch, applying at seedling and jointing stages in two batches further decreased N leaching and improved NUE. Thus, a 35% reduction of typical fertilization rate combined with applying additional N at seedling and jointing stages is recommended. From the perspective of N management, this study demonstrated optimizing field management can play a positive role in the ecologicalization of agriculture, and more field management measures should be explored.