Optimizing the nitrogen application strategies for maize in the coastal saline-alkali fields in the Yellow River Delta based on DRAINMOD-S and -N II models

Maize is one of the major grain crops in the coastal saline-alkali area of the Yellow River Delta (YRD). Rational application of nitrogen fertilizer is crucial to promote crop yield, nutrient resources, and ecological environment. In this study, the DRAINMOD-S and DRAINMOD-N II models were evaluated using a 2-year field drip irrigation experiment of maize, in order to appropriately determine the nitrogen application rate and scheme for maize. Subsequently, the proper drainage spacing was also determined. A systematic investigation was implemented to explore the effects of climate change, initial soil mineral nitrogen content, and total nitrogen application rate on plant nitrogen uptake, soil nitrogen leaching, and nitrogen storage. A multiple regression model was proposed to estimate the optimal nitrogen application rate of maize. The specific periods of nitrogen application were optimized after numerical simulation. Results showed that the DRAINMOD-S and -NII models accurately simulated the dynamics of groundwater depth, the distributions of soil salt content, and nitrate nitrogen content in the coastal saline-alkali farmland of YRD. The determination coefficients (R²) between the simulated and measured values were consistently greater than 0.80, and the normalized root mean squared error (NRMSE) was not more than 25%. According to the relationship between the drainage spacing and the soil waterlogging and salinity stress response functions (to describe the effects of environmental stress on crop yield). The drainage spacing was recommended to be 17 m in the study area. Some considerations were included the maize nitrogen requirements (meaning that plant nitrogen absorption was met own need), continuous supply of soil nitrogen (the contents of soil mineral nitrogen at harvest and at sowing were similar to each other), and nitrogen leaching risk (nitrogen leaching was as low as possible). There was a quantitative relationship between the optimal nitrogen application rate of maize and the main environmental influencing factors, including rainfall, rainfall intensity, and initial soil mineral nitrogen content, which was established and verified (R² = 0.70, P < 0.01). Moreover, a systematic investigation was made to evaluate the different combinations of nitrogen application periods or phases under 1-3 application events in dry, normal, and wet years. Some suggestions were proposed that nitrogen fertilizer can be applied either 2 times at the jointing and tasseling stages or 3 times at the jointing, tasseling, and filling stages, in terms of different hydrological years in the region. The finding can provide the theoretical basis to improve nitrogen management in the coastal saline-alkali field of YRD.