Effect Of Water Saving And Nitrogen Controlling On Nitrogrn Balance And No₃^--N Leaching Of Different Soil-Vegetable Systems Ningxia

The excessive application of nitrogen(N) fertilizers in vegetable land is common in Ningxia Irrigation Areas(NIA).This research was carried out to study the effect of different N application practices on N balance and vegetable yield.Two representative kinds of rotate system(Spring wheat-Chinese cabbage,Celery-Chinese cabbage) were adopted to study the influence of different management practices of water and N on recovery efficiency and balance;meanwhile,a two years' rotation system of tomato-tomato-cucumber-tomato in greenhouse was conducted to determine the effect of N on vegetable yield,N balance and NO₃^--N accumulation.The target N supplying rate subjected to reduced N application was put forward.The main results were as follows:1 N controlling(NC) hadn't influenced vegetable yield and N uptake.Compared with the plant yields in conventional irrigation-fertilization(W₁N₂) treatment,the yield of spring wheat in Water Saving-NC(W₂N₂) treatment increased by 6.7%, celery 12.2%,wheat after planting Chinese-cabbage yiled of W₂N₂ were 5.9%,wheat after planting Chinese-cabbage yield of W₂N₂ were 22.4%.In the planting system of tomato-tomato-cucumber-tomato in greenhouse,the first and second season tomato yields and total N uptake in N-reducing treatment hadn't differed significantly from those in conventional N treatment;but the vegetable yields in the third and fourth season decreased in N-reducing treatment,with the fourth season tomato decreasing by 48.7t/hm²ï½ž72.3t/hm² in the yield compared with that in the first season.2 The outdoor Water saving-N reducing treatment reduced apparent N losses,and the indoor N-controlling treatment reduced the accumulation of inorganic N in 0-30 cm soil layers.In the outdoor rotation system,N losses in W₂N₂ treatment were less than those in the W₁N₁ treatment and the spring-Cabbage rotation less than celery-cabbage rotation;Nmin in different N treatment were low and with minimal differences.In the indoor rotation system,the main N inputs were N fertilizers application and water irrigation,and the main outputs were N accumulation in soils and plant uptake.Plant removal of N didn't increase corresponding to the increasing N supply which was from 698 kg/hm²-882 kg/hm².The conventional N application (800 kg/hm²ï½ž1200 kg/hm²) caused a remarkable soil accumulation of N at 0～30cm depth,while the N-reducing treatment(150 kg/hm²ï½ž600 kg/hm²) significantly reduced Nmin accumulation by 58.16%～66.6%.3 The moderate levels of watering and N applying effectively controlled NO₃^--N accumulation in different soil layers.In the outdoor rotation system,NO₃^--N accumulation at different depths in W₂N₂ treatment was lower than that in W₁N₁ treatment,and spring-cabbage rotation lower than celery-cabbage rotation.In the indoor rotation system,N application at conventional rates enhanced the accumulation and downward movement of NO₃^--N in soils;while the N-reducing treatment(150 kg/hm²ï½ž600 kg/hm²) significantly decreased N accumulating amount in different soil layers(mainly 0-90 cm).4 In the in door rotation system,N application resulted in downward movement of NO3 in the top soil layer(0～30cm).The greatest N leaching occurred in cucumber-tomato rotation and at the N application rate of 600 kg/hm².The NO₃^--N movement could be traced down to 90 cm.5 A target N application rate subjected to N-controlling thus could be recommended based on the above results.In the spring wheat/celery-cabbage rotation systems,the recommended watering amounts were 3405m³/hm² for spring wheat/celery and 1767 m³/hm² for cabbage,and the N application rates were 120 kgN /hm² for spring wheat/celery and 150 kgN/ hm² for cabbage.In the indoor vegetable producing system,given a certain application rate of organic fertilizers and phosphorus-potassium fertilizers,the recommended N application rates were 100 kg/hm²ï½ž150 kg/hm² for fall-winter tomato,250 kg/hm²ï½ž300 kg/hm² for winter-spring tomato and 400 kg/hm²ï½ž450 kg/hm² for fall-winter cucumber.