[Status of soil fertility, nutrient balance, and environmental risk assessment in yam production of North China Plain].

Taking the main production area of yam in North China Plain as the research area, we analyzed the status of soil fertility and fertilizer application in yam production through field investigation and tracking monitoring, examined soil nutrient balance using the input-output model of nutrients in agricultural system, and assessed the environmental risks in the yam planting system. The results showed that: 1) the contents of soil organic matter and total N were extremely low, and the contents of available P and available Zn were both low; both nitrate and available Cu contents were at the middle level, the contents of soil slowly available K, available S, and exchangeable Ca and Mg were all extremely high, the contents of available K, available Fe, and available Mn were all at high level; 2) The nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O) inputs were 575-943 kg·hm^-2, 341-981 kg·hm^-2, and 655-1219 kg·hm^-2 during the whole growth period of yam, with chemical fertilizer accounting for 83.0%, 88.6%, and 91.3%, respectively; The input imbalance between organic and inorganic fertilizer, as well as the excessive nutrients input were prominent; 3) The surplus rate of soil nitrogen, phosphorus and potassium reached 271.14 kg·hm^-2, 466.34 kg·hm^-2, and 739.97 kg·hm^-2, with corresponding surplus ratio of 48.7%, 258.1%, and 324.5%, respectively, which all exceeded the environmental safety threshold and were classified as moderate risk, severe risk, and severe risk, respectively. The overall environmental risk caused by chemical fertilizer application in yam production had reached severe risk level.