At present, researches about effects of nitrification inhibitors dicyandiamide on growth of vegetables and migration of soil nitrogen in greenhouse were little. According to the problems of resources waste and environmental pollution in greenhouse, including the low nitrogen use efficiency in vegetables production, the declining crop yield and quality, serious N loss (NO3--N leaching,N2O emissions and NH3 volatilization) and soil salinifization. With fruit vegetables-cucumber as the research object, this experiment used biological control method (application of nitrification inhibitors DCD) combining with the different water and nitrogen management measures to study the comprehensive effects on soil-vegetables-atmosphere system. It proved adding nitrification inhibitors DCD has beneficial effects on cucumber yield,quality and soil environment. This experiment monitored N losses from three main approaches in situ and defined the number features of nitrogen gas loss(N2O,NH3).It also explored and constructed the win-win economical and environmental“optimal water and nitrogen+biochemical regulation”technical measures,which has effective resistance control on N loss.The main results are as follows.(1)DCD in the optimal water and nitrogen management had a regulating effect on N uptake of cucumber in greenhouse. It increased the nitrogen fertilizer use efficiency in plant, improved the cucumber yield. It decreased nitrate content and improved quality of cucumber.Comparing with W1N1, the nitrogen use efficiency increased by 77.65%91.38%, nitrogen agricultural efficiency increased by 98.28%142.24%. The nitrate content of cucumber among treatments of DCD decreased by 29%.The content of Vc, soluble protein and soluble sugar improved in a certain degree.(2)DCD in the optimal water and nitrogen management had an effect on N migration and transformation in soil. DCD inhibited nitrogen nitrification in soil to maintain high level of NH4+-N, and effectively suppressed NO3--N accumulation and leaching. Because of nitrification inhibition of DCD, the NH4+-N content in 030 cm soil profile in filled cucumber growth period in treatments of DCD increased by 19.27%76.93%,when comparing with W1N1. Nitrate-nitrogen below 60 cm soil layer did not change significantly with cucumber growth. Compared with W1N1, nitrate accumulate in 0180cm soil profile in treatments of DCD was reduced by 32.20%37.65%. The surplus of nitrogen in optimal water and nitrogen management reduced by 39.67%56.77%, nitrogen losses reduced by 46.49%66.93%. The apparent loss in W2N4+DCD was the lowest with the value of 243.31 kg·hm-2,loss proportion of 64.71%.(3)DCD in the optimal water and nitrogen management improved soil environment quality in a certain degree. DCD can weaken depline of the soil pH value caused by nitrogen application, and had a buffer action on it.The soil CEC in DCD treatments were improved to a certain extent. There was no significant difference among them. The total salt content in the treatments of DCD was always lower than W1N1 in different growth stages,and had a little change after uprooting.(4)DCD in the optimal water and nitrogen management significantly influenced ammonia volatilization from soil. The ammonia emissions of the optimal water and nitrogen management with DCD last longer than the conventional water and nitrogen management. The peaks of ammonia volatilization in treatments of DCD were lower than W1N1 significantly.Compared with the conventional water and nitrogen management, the accumulative N loss by NH3 volatilization from the three treatments of DCD decreased 55.97%, 43.68% and 66.47%, respectively. The loss rate of NH3 volatilization from urea nitrogen in W2N2+DCD,W2N3+DCD and W2N4+DCD was 3.47%, 3.80% and 3.17%, respectively, and there was no significant difference among them. There were also no significant differences between W2N3+DCD and W1N1.(5)DCD in the optimal water and nitrogen management effectively reduced N loss as N2O emissions. The N2O flux in different treatments of water and nitrogen management got to their peaks after four days of fertilization and irrigation, and then continued to drop. The peak emission and accumulative emissions of N2O from three treatments of DCD(W2N2+DCD, W2N3+DCD and W2N4+DCD)were all less than that in W1N1 significantly in four top dressing stages. There was no significant difference among them. Compared with W1N1, the accumulative emissions of N2O from the three treatments of the optimal water and nitrogen management decreased by 63.32% 75.31%. The loss rate of N2O emission from urea nitrogen and the contribution rate of nitrogen on N2O loss in W2N4+DCD was the lowest, with the value was 0.34% and 69.41%, respectively.(6)In general,the optimal fertilization in greenhouse cucumber was 376 kg·hm-2 topdressing and 10% DCD of nitrogen.It had an effective resistance control on N loss,to achieve economic and environmental benefits. |