Effects Of Nitrification/Urease Inhibitor On Nitrogen Migration, Transformation And Reape Growth

Nitrogen is an essential element for plant growth. Nitrogen leaching and runoff losses from arable land because of excessive nitrogen application and unreasonable management measures, which causes contaminations of underground water and surface water, have become a worldwide environmental concern. Vegetables demanded have converted from quantity to quality with the rising of living standard. So scientists have put forward biological inhibitors to control urea hydrolysis and nitrogen nitrification, and to reduce the excessive accumulation of nitrate in vegetables. It plays an important role in control nitrogen fertilizer pollution, also reduce vegetables'nitrate content and enhance the nitrogen use efficiency.This experiment had adopted pot experiment and soil column in greenhouse, to study the effects of nitrification inhibitor Dicyanamide (DCD) and urease inhibitor N- (n-Butyl) thiophosphoric triamide (NBPT) and the two combined application on rape growth and nitrogen utililization, also to study nitrogen migration and transformation when different fertilizer levels applied in 90cm soil column, including nitrate-N, ammonium-N and pH monitored in leaching water.The experiments results showed as follows:1. When nitrification/urease inhibitor added, it could improve the rape yields, and reduce nitrate content in rape. When DCD was applied to urea for the amount of 1%, 2%, 3%, 4%, 5% of nitrogen application, it could significantly increase the biomass of rape and reduce the rape nitrate accumulation by 22.77%~33.50% and 23.87%~30.51%, respectively. Add NBPT to urea could significantly improve the rape yield by 30% and reduce nitrate accumulation highly by 32.63% when was at 0.5%, 1.0%, 1.5%, 2.0%, 2.5%. DCD and NBPT combined application could increase the yield of rape, and when DCD was at 0.5%, NBPT was at 0.25%, it reached significant level by 46.22%. The nitrate in rape showed decreased first and then increased. When the inhibitors were in lower level, they were able to reduce nitrate accumulation.2. When nitrification/urease inhibitor added, it could enhance N use efficiency. When DCD 3% was applied to urea, it could significantly improve nitrogen use efficiency by 6.66 percentage points. When NBPT was at 0.5%, the total N and N uptake were higher than others, and N use efficiency could be improved by 5.65 percentage points. Application of DCD and NBPT mixed, DCD2.0%NBPT1.0%, DCD2.5%NBPT1.25% significantly increased N uptake and nitrogen utilization, respectively, higher compared to NPK by 3.23 and 5.48 percentage points.3. When nitrification/urease inhibitor added, it had some effects on N residue. The nitrate content in soil decreased with DCD applied more. When DCD was at 1%, it could significantly increase N residue, while at 5%, decreased significantly. NBPT resulted in about 45.11% ~ 58.29% N residue in the soil, and most treatments were more than 50%. When NBPT was at 2.0%,2.5%, it could significantly reduced N residue. DCD and NBPT combined application had resulted in about 44.74% ~ 62.78% of the N residue, and when DCD0.5%, NBPT0.25% significantly reduced the proportion of urea in the soil.4. Under lower fertilization conditions, nitrate leaching in DCD treatments could delay the peak time for 7 days throughout the trial period, and also reduce the peak value. Added NBPT alone, more likely to make nitrate leach in early time, and have the higher peak, but then decreased rapidly, and maintained low nitrate concentration in later time. DCD or NBPT added alone, could not significantly reduce the accumulation of nitrate leaching, but the mixed used was able to reduce the nitrate accumulation.5. In the higher fertilizer conditions, DCD throughout the monitoring period had a better effect to retard nitrogen leaching, and NBPT, DCD and NBPT combined application, had a good effect in later period. The three treatments could significantly reduce 13.73%, 11.61%, 17.15% of the cumulative amount of nitrate leaching.6. The single DCD or NBPT application in lower fertilization conditions, inorganic nitrogen content in leaching water increased by 13.72% and 1.87%, and had no reduction on inorganic nitrogen leaching losses, but DCD and NBPT mixed treatment, reduced 13.86%. In higher fertilization conditions, DCD, NBPT and co-application of DCD and NBPT, could reduce 7.49%, 13.24%, 19.53%, respectively.7. pH of leaching water had a negative correlation with the concentration of nitrate content, and showed a positive correlation with the concentration of ammonium nitrogen. Under the low and high fertilizer, the pH dropped by 0.07~0.19 units at the end. When nitrate concentrations reached the peak point under higher fertilizer, it could significantly descend pH by 0.39 units. DCD, NBPT, DCD and NBPT combined application could minimize changes on too low and too high pH under high fertilization.