Effect Of Nitrification/Urease Inhibitors On Vegetable Growth And Soil Nitrogen Transformation Under Negative Pressure Irrigation

The excessive application of nitrogen(N) fertilizer and unreasonable management measures in current vegetable production have resulted in large amount of nitrogen loss, and reduced the nitrogen use efficiency. Among them, the nitrate leaching in soil is one of the important ways of nitrogen loss, and is also the important reason of nitrate pollution of groundwater. In order to improve the nitrogen use efficiency and reduce the environmental pollution of nitrate leaching, coordinating the soil nitrogen transformation process through nitrification inhibitors and urease inhibitors is an effective way. Negative pressure irrigation is a new type of water-saving irrigation technology, which used with water soluble fertilizer can realize continuous water and fertilizer supply depending on crop growth.Through pot experiment, this paper researches the effects of decreased nitrogen with nitrification inhibitors(DCD) and urease inhibitors(HQ) addition under the negative pressure irrigation on cucumber and rape growth and soil nitrogen transformation, and compares the inhibition effect of different nitrogen levels with inhibitor combinations, and discusses the inhibition mechanism of nitrification inhibitors and urease inhibitors on soil nitrogen transformation related soil enzyme and ammonia oxidizing bacteria. This study is of great significance to reduce nitrate accumulation of vegetables, improve the nitrogen use efficiency and control the environmental pollution of nitrogen.The experimental results showed that:(1) In cucumber pot experiment, the 10%-30% reduction of fertilizer N with nitrification and urease inhibitors addition could remain close cucumber yield to conventional fertilizing amount treatment, reduce the nitrate content of cucumber fruits by 7.1%~33.9% and promote the cucumber fruits on the absorption of nutrients. Among them, the effect of 10% reduction of nitrogen with added nitrification and urease inhibitor treatment(0.9:0.7:1+10% DCD+1%HQ+M) was the best.(2) In rape pot experiment, under the condition of the same fertilizing NPK amount, nitrification and urease inhibitors addition could significantly increase the rape yield by 25.2%, and significantly reduce the nitrate content by 51.9%, meanwhile improve the nutrients content of rape, which made the nitrogen use efficiency significantly increased by 85.2%. The 15% and 30% nitrogen decreased with nitrification and urease inhibitors addition also promoted rape yield, quality, nutrient content and nitrogen use efficiency, among them, the effect of decreased 30% nitrogen with nitrification and urease inhibitor addition treatment T5(0.7:0.5:1+ 10%DCD+1% HQ+M) is more prominent.(3) During rape growth period, all of the combined application treatments of nitrification inhibitor DCD and urease inhibitors HQ could inhibit ammonium oxidation process in the soil, slow the urea hydrolysis by reducing the soil urease activity, and reduce nitrate accumulation in the soil by improving the soil nitrate reductase activity, thus improve the NH4+-N content in soil, reduce the NO3--N content, and make the nitrification delay. Among them, the treatment with inhibitor addition T3(1:0.5:1+DCD+HQ) could remain significantly inhibitory effect for 1-15 d after fertilization time. Soil determination results after rape harvest showed that, all the treatments applied nitrification and urease inhibitor could reduce the diversity of ammonia oxidizing bacteria in the soil. Compared with the conventional nitrogen treatment T2, the treatment applied inhibitor T3 decreased the chao1 index and shannon index of ammonia oxidizing bacteria in the soil significantly. Comprehensive analysis showed that, the conventional N application with nitrification and urease inhibitors addition treatment T3(1:0.5:1+ 10%DCD+1%HQ+ M) and 30% reduction of nitrogen with nitrification and urease inhibitors addition treatment T5(0.7:0.7:1+10%DCD+1%HQ+M) had a good application prospect, which could significantly improve rape yield, nitrogen use efficiency and quality, and have obvious inhibiting effect on soil nitrate nitrogen residual.