Effects Of Nitrification Inhibitor On The Transformation Of Urea And Greenhouse Gas Emission In Vegetable Field

Nitrogen is an essential element for plant growth. The nitrate leaching easily contaminates water and the denitrification can cause losses of nitrogen gases and even the greenhouse effects, which is detrimental to the environment and the economy. In order to inhibit the nitrification, reduce greenhouse gases and improve nitrogen use efficiency, we discuss the optimal dosage and application methods of nitrification inhibitor.In this study, we take aerobic soil incubation experiment and field experiment. The incubation experiment was carried out to study the effects of different levels of the nitrification inhibitor dicyandiamide （Dicyandiamide, DCD） on the transformations of nitrate nitrogen and ammonia nitrogen. Thus we can determine its optimal dosage. In field experiment, we plant cabbage to discuss the effects of single application of DCD and other combined modulators on nitrogen transformation, N₂O emissions, ammonia volatilization losses, and nitrogen use efficiency.The main conclusions of this study were as following:1. The incubation results showed that during the 44 day incubation period, the application of DCD significantly delayed the transformation from NH₄⁺-N to NO3--N. The apparent nitrification rate of the reaching balance date of them delayed 7 days, 14days, 14days, and 21days at the levels of 1%, 2%, 3% and 4%, respectively. It has showed a rising trend until the incubation end at the level of 5%, always lower than the control. Within 20 days the DCD treatments maintain high NH₄⁺-N concentrations, and after 30 days the NO3--N concentrations still grow.2. We concluded through the field experiments that nitrification inhibitor increased the NH₄⁺-N contents in 0-40cm layer, and reduced the movement of NO3--N to 40-100cm layer. Nitrification inhibitor reduced soil N₂O emissions. The urea treatment reached peak of N₂O emissions at the 3rd day after fertilization, and then declined rapidly. The nitrification inhibitor delayed the N₂O peak. When the treatments were 4%DCD, compound inhibitor A（4%DCD+3g modulators+15g ammonium molybdate） and compound inhibitor B（4%DCD+5g modulators+25g ammonium molybdate）, the N₂O peak delayed for 2 days, 2 days and 3 days. Within 49 days, the accumulating N₂O flux of treatments with nitrification inhibitor were lower than urea treatment, and they decreased by 15.28%、23.92% and 29.57%. The treatments compound inhibitor B and 4%DCD had significant differences. The nitrification inhibitor increased NH₄⁺-N contents in vegetable field, so it increased the risk of soil ammonia volatilization losses. The treatments of 4%DCD, compound inhibitor A（4%DCD+3g modulators+15g ammonium molybdate） and compound inhibitor B（4% DCD+5g modulators+25g ammonium molybdate） respectively increased cumulative ammonia volatilization losses by 24.59%、15.47% and 18.24% compared with the urea control. Only 4%DCD treatments reached significant differences. The compound inhibitor A and compound inhibitor B treatments did not significantly increase soil ammonia volatilization losses.3. Nitrification inhibitor reduced the NO3--N contents both in soils and cabbages. The yield and N uptake increased. The nitrogen use efficiency of 4%DCD, compound inhibitor A（4%DCD+3g modulators+15g ammonium molybdate） and compound inhibitor B（4% DCD+5g modulators+25g ammonium molybdate） increased by 63.74%、94.24% and 62.30%.4. Totally: The treatment compound inhibitor A（4%DCD+3g modulators+15g ammonium molybdate） is more effective in nitrogen use efficiency and low environment pollution than other treatments, and it has a better application prospect.