The Nitrogen Fertilizer Use Efficiency And Soil Quality Variation Of Vegetable-soil System In Yangse Delta Area

[n recent years, the planting structure of agriculture has changed a lot in China. Vegetable planting area developed rapidly in a large scale. In vegetable cropping system, a great deal of nitrogen fertilizer and manure were used for the high benefit of it, which lead to the decline of nitrogen use efficiency, the degradation of soil quality and environment pollution. In Yangtze delta area, the developed region of economy in China, the intensive agriculture production with high fertilization level leads to environment pollution much more seriously. So to study the fate and transformation of nitrogen fertilizer in vegetable-soil system and the soil quality variation in this region is very important, which may give the guidance to the vegetable growers to grasp the rational application of fertilizer and as well as reduce the environmental pollution.Two field trial of greenhouse, one field orientation monitoring trail and one pot experiment were conducted to study the fate of organic nitrogen and fertilizer nitrogen in vegetable-soil system. The difference method and ¹⁵N isotope method were adopted together and the cross label technique was utilized in this study. In addition we investigated the soil quality of different type of rotation and different planting age of vegetable greenhouse cultivation. The main results as follows:The results of general field trials showed that nitrogen use efficiency less than 10% of the first vegetable crop under the follow condition nitrogen application dose 225-600 kg N·hm^-2 and the proportion of organic fertilizer between 0-100 percent. The sum of N use efficiency of two crop rotation was only 5-22%. The N remained in soil was mainly as the forms of NO₃^--N and NH₄⁺-N in 0⁴0cm depth. The apparent N recovery of soil was 34-90%. In addition, N use efficiency was improved with the manure rate of organic N/fertilizer N. The results of ¹⁵N isotope trial showed that only 2-11% of the nitrogen absorbed by vegetable was derived from fertilizer, and about 90% vegetable nitrogen came from soil. Because of the rainstorm, fertilizer nitrogen leakage was serious and about 70% fertilizer nitrogen lost. However, manure fertilization increased nitrogen recovery of soil. And fertilizer nitrogen recovery of soil was much more when fertilizer and manure employed together than that fertilizer employed only. However still about 97% of the nitrogen loss was from fertilizer and only 3% was from manure when at the mixed fertilization.Survey study was conducted on three types of vegetable field including vegetable-paddy rotation, three-year vegetable greenhouse cultivation and 10-year vegetable greenhouse cultivation, which represent low, medium and high soil nitrogen level separately. The results showed that soil productivity improved so that vegetable yield and nitrogen uptake increased with the soil nitrogen level. When the same dose of nitrogen fertilizer was used, the degree of enhancing effect in productivity declined with soil nitrogen level. In the field of the low and medium nitrogen level, vegetable yield and nitrogen uptake of fertilization treatment were all more than that of control treatment. On the contrary, in the field of high soil nitrogen level, the yield of fertilization treatment was lower than that of control treatment. The nitrogen use efficiency, N recovery rate of soil and vegetable were all decreased but nitrogen loss rate increased with soil nitrogen level. The nitrogen use...