Effect of different phosphorus application rates on soil nitrate leaching in vegetable fields

【Objectives】 The effect of different phosphorus application rates on nitrate leaching was studied in two vegetable soils of Wuhan in order to provide theoretical evidence for optimum phosphate fertilization practice and to secure the safety of vegetables.【Methods】 The experiment was carried out on undisturbed soil core with two soils (silty clay and silty clay loam) collected from vegetable fields of Huazhong Agricultural University and Xinzhou Hubei, respectively. Both soils were common vegetable soil in Wuhan suburb areas, and four different vegetable species (Chinese cabbage, pepper, amaranth and radish) wereselected and planted under continuous cropping according to their seasonal adaptability. Four phosphorus (P) application rates as P2O5 (0, 125, 250 and 375 kg/hm2) were applied, and the application rates of nitrogen (N) and potassium (K) in all treatments were N 750 kg/hm2 and K2O 500 kg/hm2, respectively. Precipitation was 1043.0 mm per year and the irrigation volume was 120.1 L per year during the experimental period. Leachate was normally collected every 15 days in autumn and winter, and every 10 days in spring and summer, while it was also collected depending on the precipitation. Volumes were recorded and NO-3 concentration was determined in the leachate. After harvesting, vegetables were weighed and total N concentration in vegetables (dry weight basis) was determined. 【Results】 1) Phosphorus application significantly increased the yield of all four vegetables, compared with no P application. Yield on silty clay was significantly lower than that on silty clay loam, which was about 1.63-2.36 times different. 2) Nitrogen uptake in Chinese cabbage, amaranth and total N accumulation of four vegetables increased significantly with increasing of P application rate. N accumulation in silty clay loam was markedly higher than that in silty clay. 3) Different P application rates did not affect the total volume of leachate (except 125 kg/hm2 treatment in silty clay loam) with higher amount on silty clay than that on silty clay loam. 4) Phosphorus application decreased or significantly decreased NO-3 concentration in leachate (except amaranth on silty clay) with the effect increased with increasing P application rate. On average, NO-3 concentration of four vegetables decreased by 38.6% (silty clay) and 28.85% (silty clay loam), respectively. 5) Total amount of nitrate leaching for all vegetables (except amaranth) decreased with P application. It decreased with increasing P application rate on silty clay, but on silty clay loam, it dropped firstly and then increased. Total amount of leached nitrate was higher on silty clay than on silty clay loam, it was decreased by 26.4%-33.7% and 23.5%-39.9% with P application in the two soils, respectively. 【Conclusions】 Phosphorus application increases vegetables production and N accumulation, thus decreasing the amount of NO-3 leaching in both two soils. Soil texture is an important factor which affects NO-3 leaching in which the amount of NO-3 leaching is remarkably lower in silty clay loam than in silty clay. It is concluded that the application of P2O5 250 kg/hm2 in silty clay loam can increase vegetable yield and decrease NO-3 leaching, while in silty clay soil P2O5 375 kg/hm2 is the recommended application rate.