农业耕作对三峡水库支流库湾消落带土壤氮、磷含量及流失的影响

三峡水库低水位运行时，消落带由于落干期与作物生长期重叠，常被近岸农民开垦利用，然而传统的农业种植可能会影响库区水环境.为对比农耕和弃耕的水环境效应，选择一级支流澎溪河库湾消落带为研究区域，以玉米、土豆和花生地为研究对象，选择农耕期（2018年3~9月）和退耕期（2019年3~9月）对农耕地和弃耕地土壤各氮、磷形态含量进行研究，同时构建了农耕地与弃耕地氮、磷平衡模型，比较分析农耕和弃耕状态下土壤氮、磷收支特征及其流失风险.结果表明，玉米地土壤氨氮、全磷和无机磷含量在不同种植期差异显著；农耕地的氨氮和硝态氮的含量显著高于弃耕地，全磷、无机磷和钙结合态磷的含量显著低于弃耕地；土壤氮、磷盈余量大小顺序为玉米>土豆>花生，分别是76.89、51.92和43.74 kg·hm^-2以及79.69、75.76和17.78 kg·hm^-2，整体上，3种作物用地氮、磷盈余量大于流失风险值，研究区农耕地氮、磷污染潜势呈现.综上可知，消落带农业耕作将迫使氮、磷流失风险加剧，不利于水环境保护.

Effects of Farming Practices on Soil Nitrogen and Phosphorus Concentrations and Its Loss in the Drawdown Area of the Tributary Embayment of the Three Gorges Reservoir

As the Three Gorges Reservoir (TGR) periodically operates at low water levels, its drawdown area has been utilized for cultivation by local farmers due to the overlap of the non-inundated period and the crop-growth period. However, traditional agricultural planting may affect the aquatic environment of the TGR area. To explain the effects of agricultural farming and abandoned farming on the water environment, a study was conducted in the drawdown area in an embayment of the Pengxi River (a tributary of the TGR). Corn, potato, and peanut fields were investigated for nitrogen and phosphorus content in surface soil, during the farming period (March to September 2018) and the conversion period (March to September 2019). Nitrogen and phosphorus balance models were constructed for farmland and abandoned farmland, to compare and analyze the budgets and loss risk of nitrogen and phosphorus from soil in the drawdown area. The results showed that the ammonia nitrogen (NH₄⁺-N), total phosphorus (TP), and inorganic phosphorus (IP) content of soil in the corn field varied significantly across different planting periods. The concentrations of ammonium nitrogen and nitrate nitrogen (NO₃^--N) were significantly higher in farmland soil than in abandoned farmland soil, and the concentrations of total phosphorus (TP), inorganic phosphorus (IP), and calcium-bound phosphorus (Ca-P) were significantly lower in farmland soil than in abandoned farmland soil. The different soils were ranked according to the intensity of nitrogen and phosphorus surplus as follows:corn field>potato field>peanut field. The apparent surplus values in the different farmland soils were 76.89 kg ·hm^-2(corn field), 51.92 kg ·hm^-2(potato field), and 43.74 kg ·hm^-2(peanut field) for nitrogen, and 79.69 kg ·hm^-2(corn field), 75.76 kg ·hm^-2(potato field), and 17.78 kg ·hm^-2(peanut field) for phosphorous. Overall, the surplus intensities of nitrogen and phosphorus in all three croplands were higher than the respective risk thresholds, indicating potential nitrogen and phosphorus pollution in the three farmland types. Agricultural farming in the drawdown area may therefore increase the risk of nitrogen and phosphorus loss and is not conducive to the protection of the aquatic environment.