Optimized Management Of Nitrogen Fertilizer And Strategies For Reducing Nitrogen Leaching Loss In Greenhouse Vegetable Field In Taihu Lake Region

This study was conducted in a field experiment under the representative greenhouse vegetables-lettuce, celery and tomato rotation in Wuxi city, which is located in Taihu Lake region. This research was observed the effects of five nitrogen (N) fertilizer application rate:no N addition (N1), conventional N rate (N5),25%(N4),40%(N3) and 60%(N2) of the conventional N rate on greenhouse vegetable yield, quality and root morphological characteristics and soil nitrate accumulation, In addition, observed the rule of N leaching loss and strategies for reducing N Leaching loss in greenhouse vegetable field in Taihu Lake region.The main results as follows:The greenhouse vegetable yield was not impact in experimental region when the N application rate has reduced by 25～40%.The optimized N application rate in celery and tomato were 338.2 and 277.6 kg/hm2, respectively. The nitrate content in both vegetables significant increased to coincide with the increased N rate, and there was a significant positive correlation between them. The vitamin C content had a waving change as N rate decreased, and the highest content of all the N rate was the 40%(N3) of the conventional N rate treatment.The soil nitrate-N accumulation in soil was proportional with the N rate, and the soil nitrate-N content was increaseing from 35 mg/kg to 359 mg/kg after three greenhouse vegetable was cultivated under the conventional N rate. The soil conductivity and pH values were significant correlation with the soil nitrate-N content, but the soil conductivity was more significant than the soil pH value. The correlation coefficient between soil nitrate-N content and soil conductivity was 0.832.40% of the conventional N rate significantly enhanced lettuce root growth, included the increasing of the root surface area, volume and total root length; and the highest yield and vitamin C contents of all the N rate were also in 40% of the conventional N rate.The nitrate-N concentration of leaching water was directly affected by the N rate, and the highest concentration was in conventional N rate. The leaching peak was occured in the summer fallow period (from July to September), and the nitrate-N leaching and total N leaching were up to 97.3 and 109.2 kg/hm2 in this period, which accounted for 30% of the total leaching amount in a whole year. Compared to conventional N rate,40% of the conventional N rate could reduce 12.9% and 17.7% N leaching loss in tomato and lettuce season, respectively, and no yield loss.Cultivated catch crop in the fastigium of the N leaching can reduced the N leaching loss. Compared to fallow treatment (no catch crop cultivation), cultivated catch crop sweet corn can significantly reduce 8.34%～68.79% of the soil residual nitrate-N in 0-50 cm soil layer, can reduce 2.89%～76.20% of the nitrate-N leaching loss, and no yield loss in subsequent vegetable season.