Water Drainage And Nitrate Leaching Of Vegetable Field Under Water And Nitrogen Management

A 4-yr field experiment was carried out at China Agricultural University Field station in suburb of Beijing. A vegetable sequence system (Cauliflower-Amaranth-Spinach) used by farmer was set up. The objective was to analyse the effects of different water and N-fertilizer management methods on vegetable yield, nitrate content of vegetable and the relationship among losses of nitrogen and nitrogen applied in vegetable field and water drainage and nitrate leaching of vegetable field. Soil water content in soil profile, soil water potential at the depths of 75 cm and 105 cm and extraction of the soil solution at the depth of 90 cm were determined with TDR (Time Domine Reflectometry), tensiometers and sceramic suction cups respectively. The amount of nitrate leached was calculated by using Darcy's law. The results are as follows:The yield of vegetable was not significantly decreased when soil water content was held between 50% and 80% PESW (plant extractable soil water) in the rooting zone of the vegetable crops and applied N-fertilizer amounts decreased to 20%-40% of that of traditional N-fertilizer treatment.Nitrate content of vegetable was mainly affected by nitrogen content in soil, which increased with increasing nitrogen content in soil by appling N-fertilizer. Nitrate content of vegetable was increased 13%-97% in traditional treatment than that of the other nitrogen treatments. Changes of nitrate content of vegetable were low when soil water content was changed. Nitrate content of vegetable was very high uncertainty ranged from 0.6-13%.Reducing irrigation during vegetable growth period water drainage quantity was obviously decreased and nitrate leached quatity were obviously reduced. In Nl, N2 and N3 treatments water drainage amount was 5.2 times, 3.9 times and 1.1 times, the amount nitrate Jeached was 4.6 times, 4.7 times and 1.5 times of that of improved in traditional water treatement respectively.Decreasing applied N-fertilizer amount nitrate leaching quatity was reduced in traditional water treatment. The amount of nitrate leached was increased by 84% and 86% than that of N2 and N3 in Nl treatment, and was increased by 14% than that of N3 in N2 treatment. But in improved water treatment nitrate leaching quatity was the lowest in N2 treatment, which was of 16% of that of Nl treatment and 42% of that of N3 treatment. The amount of nitrate leached should be increased when applied N-fertilizer amount was higher or lower in improved water treatment. But applied N-fertilizer amount was the main factor to affect nitrate concentration of soil solution at the depth of 90 cm in the vegetable field. Nitrate concentrations of soil solution in traditional N-fertilizer applied treatment was higher than that of the other N-fertilizer applied treatments.Water drainage was controlled by rainfall during farrow duration. Nitrate leached was controlled by rainfall during farrow duration and residue Nmin in the soil. Nitrate leaching was increased of raifall high with water drainage high and increased N-fertilizer applied with residue Nmin in the soil in annual and was of 22%-44% of that of the whole experiment in different treatment.In a word, improved water and N-fertilizlizer mangement was suggested. Concent of nitrate of vegetable was decreased and water drainage and NO3-N leaching amounts wete reduced obviously, water and N-fertilizer usage efficency was increased, but vegetable yields were decreased.