Excessive fertilizer application in the cropping industry leads to excessive nitrogen and phosphorus in surrounding water bodies, which causes farmers to increase economic cost and damage the environment. To address the problem, we built a crop-soil runoff soil column test system, setting eight fertilizer application levels for eggplants. Then, crop yield, soil fertility and pollutant concentrations in the receiving water bodies were measured. The process of fertilizer application on the water quality of surrounding receiving water bodies and the rationality of fertilizer application were analyzed. The results showed that crop yield, soil fertility, and pollutant concentrations in the receiving water increased with the increase in fertilizer application. The crop yield stabilized when the fertilizer application amount was higher than 0.12 kg/m²; the concentrations of total nitrogen (TN) and total phosphorus (TP) in the water increased significantly with the increase in fertilizer application, where particulate nitrogen (PN) and organic phosphorus (OP) were the key pollutants. In addition, crop growth had an interception effect on pollutant migration. The concentration of pollutants in the water was significantly lower in the late crop growth period (after flowering) than in the early. The crop had the best interception effect on pollutants when the fertilizer application was 0.12 kg/m². The concentrations of TN and TP in the water were 29.7% and 22.3% after the flowering period, being lower than those before the flowering period. Therefore, a reasonable value of 0.12 kg/m² is recommended for fertilizer application in this article. It can provide a reference for the fertilization system of eggplant planting in North China and theoretical support for the realization of clean production in small rural watershed planting.

In the recent decades, the issue of water-resource security of the Daqing River Basin, which is one of the five major rivers in the Haihe River Basin, has become increasingly serious affected by climate change and human activities. In this paper, a dynamic simulation and early warning model of water quantity and quality in this basin based on the SWAT model was constructed to promote the implementation of water environment quality and safety bottom line in the Beijing-Tianjin-Hebei region. The results of the study are as follows: (1) When encountering a once-in-a-century rainstorm, the flood pressure of Zijingguan in the flood season is the highest, with the highest water level reaching 521.23 m, and the overall maximum runoff follows the order of Zijingguan > Fuping > Zhangfang. (2) When the NH₃-N emissions are reduced by 37.64~85.10% in each month (based on the level in 2017), the water quality at the outlet of the basin can reach the standard, and the upper limit of NH₃-N emissions is 504.5 t/m. (3) The regulation and control scheme seeking to “ensure the base flow with standard water quality” and “optimize NH₃-N annual emission” is proposed in this paper. The NH₃-N concentration at the outlet of all watersheds can reach the standard when the basic runoff of each sub-basin reaches 0.01 to 10.32 m³/s. In addition, concentrating the emission in July, August, and September and reducing the emission intensity of NH₃-N in proportion can significantly reduce the monthly average NH₃-N concentration (<1.99 mg/L) at the outlet section of the basin.