摘要

Nitrate leaching from intensive vegetable production is an important contributor of nitrate contamination of water resources. The aim of this study was to quantify NO3 (-) leaching losses under intensive vegetable production as affected by different rates of N fertilizer and to determine the optimum N application rates both for vegetable production and for meeting the drinking water standard. Twelve undisturbed soil lysimeters (590 mm diameter and 650 mm depth) were collected and installed in a field lysimeter facility in Central China to study nitrate leaching from a clay loam soil (alfisol) under irrigated vegetable production conditions. Urea was applied at 0 kg N/ha (N0), 370 kg N/ha (N1), 1,110 kg N/ha (N2), and 1,480 kg N/ha (N3) to the lysimeters planted with vegetables. Nitrate leaching losses and vegetable yields were measured for five vegetables [capsicum (Capsicum annuum L.), amaranth (Amaranthus mangostanus L.), radish (Raphanus sativus L.), Chinese cabbage 1 (Brassica chinensis L.), and Chinese cabbage 2), with rotations lasting a total of 13 months. The results showed that NO3 (-)-N leaching losses were significantly affected by urea-N application rates, increasing from 32.8 to 63.3, 227.1, and 353.7 kg N/ha in the N0, N1, N2, and N3 treatments, respectively. These leaching losses represented 8.2%, 17.5%, and 21.7% of the total N applied, respectively. The average NO3 (-)-N concentration in the drainage water ranged from 3.7 to 43.1 mg N/L. Only the NO3 (-)-N concentrations of the control and N1 treatment were below the drinking water standard (10 mg N/L). Plant N removal accounted for 38.3%, 29.7%, and 22.9% of total N applied in the N1, N2, and N3 treatments, respectively. The N application rates for maximum yield, 90% maximum yield, and for meeting the drinking water standard (10 mg N/L) were 1,098.4, 699.5, and 445.2 kg N/ha, respectively. These results showed that the intensive vegetable production systems with high N fertilizer application rates and irrigation have a high NO3 (-) leaching potential. Both the N application rates for optimum economic yield and for meeting the drinking standard were much lower than those often used by local farmers pursuing excessively high yields. The optimum fertilizer N application rate should be set as that which would not result in the NO3 (-)-N concentration in the leachate above the drinking water standard. This rate is often lower than that for 90% maximum production.