Study On Nitrogen Fertilizer Use Efficiency And Characteristics Of Nutrient And Salt In Vegetable Fields

With the adjustment of agricultural planting structure, protected cultivation of vegetable field is applied rapidly in a large scale in our country. A great deal of fertilizer or manure were used by peasantries in protection cultivation of vegetable field in order to gain the high benefit, which led to soil nutrient imbalance, the deterioration of ecological environment, and so on. At present, we did not have sufficient data of field in-situ trials about nitrogen use efficiency of protected vegetable. It was difficult to draw reliable conclusions about nitrogen efficiency. Some experiments were showed that the accumulation of soil nutrient and salt were serious on the old protected vegetable field. We researched the soil nutrient and salt of protected vegetable field in different areas and testified the trend.On multi-point field in-situ, the nitrogen use efficiency of vegetable with new protected field (below 5 years) and old protected field (over 10years) and CK (crop field) were conducted by ¹⁵N isotope method and routine difference method in Jiaxing and Kunming, 4～10 replicates every treatment. Meanwhile, Site-specific fields were monitored in Jiaxing, Zhejiang Province, Kunming, Yunnan Province, Shouguang, Shandong Province, and Shenyang, Liaoning Province. we studied the cumulative characteristics of nutrient and salt of different soil depth. The main results are showed as follows:Nitrogen use efficiency of vegetable was 11.6% in Jiaxing and Kunming on 17 points of ¹⁵N isotope trial. With the protected cultivating years increasing, nitrogen use efficiency of vegetable decreased significantly, nitrogen use efficiency of vegetable was 14.2% in new protected field,and 9.0% in old protected field. Nitrogen use efficiency of crop was 17.2% in field.¹⁵N isotope trial showed nitrogen residue was high in protected field. The soil residue of 0～80cm depth was 250～286 kg/hm² with 300～450 kg/hm². Nitrogen residue decreased with soil depth increasing. Nitrogen residue in soil surface(0～20cm) was significantly higher than that under the soil, and accounted for 53.4%～65.9% of total nitrogen residue. Nitrogen residue of protected vegetable field was significantly higher than crop field.The content of total nitrogen, total phosphorus surface (0～20cm) soil on protected field were 1.4 times, 3 times of crop field in Jiaxing, Zhejiang Province, Kunming, Yunnan Province, Shouguang, Shandong Province, and Shenyang, Liaoning Province. the nitrate, ammonium nitrogen and phosphorus content were 8 times, 6 times and 11 times. The content of nitrate, ammonium nitrogen and phosphorus decreased with soil depth.The pH value in 0～5cm, 5～20cm and 20～40cm of old protected field were significantly higher than new protected field, and no significant changes below 40cm soil depth. The pH value in 0～5cm surface soil was significantly lower than that under soil depth. Soil pH was negatively correlated with the nitrate and phosphorus content, which indicated that accumulation of the nitrate and phosphorus in soil was the main factor inducing soil acidification.Salt content in soil surface (0～20cm) of protected field was significantly higher than that of crop field. The content of salt decreased significantly with soil depth. There were no different between new protected field and old protected field. The accumulation of soil salt displayed apparent phenomena in Jiaxing, Zhejiang Province, Kunming, Yunnan Province, Shouguang, Shandong Province, and Shenyang, Liaoning Province. The content of SO₄^2-, NO₃^- Cl^-,Ca²⁺, K⁺+Na⁺ in topsoil (0～5cm) of protected field were increased significantly than crop field topsoil.