A lysimeter study of nitrate leaching and optimum nitrogen application rates for intensively irrigated vegetable production systems in Central China

Background, aim, and scopeNitrate 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.Materials and methodsTwelve 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.ResultsThe 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.DiscussionThese 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.Recommendations and perspectivesThe 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.

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