| It is common that excessive nitrogen fertilizer is applicated in vegetable greenhouse,which has been resulting in serious nitrogen leaching, emissions of nitrous oxide and ammonia volatilization pollution. The report is less on nitrogen loss and the biological control of the pollution in tomato greenhouse. The methods of combining the field investigation and field plot experiment were used to investigate that soil physicochemical properties variation with the excessive fertilization in tomato greenhouse, to understand the effects of nitrogen fertilizer with Dicyandiamide(DCD) on nitrate accumulation in 0-100 cm soil profile, nitrate leaching, nitrous oxide emissions and ammonia volatilization in tomato greenhouse with excessive nitrogen application, which could reduce the application of nitrogen fertilizer for improving nitrogen efficiency and preventing and controlling fertilizer pollution. The main results and the characteristics of innovation are as follows:1. The soil physical and chemical properties of tomato greenhouse were surveyed in Yongqing County. The results showed that there were relationships between the main nutrient index and cultivating years. Moreover, organic matter and N, P and K nutrient elements in 0-20 cm soil accumulated with increasing planting years. During the age of greenhouse in 1-9 years, an average annual increase of organic matter, alkaline hydrolysis nitrogen, available phosphorus and available potassium respectively were 0.19%, 22.3mg/kg, 17.46 mg/kg and 167 mg/kg. The content of alkaline hydrolysis nitrogen was at range of 112-311 mg/kg. The content of available phosphorus ranged of 3.7-290 mg/kg in soil. The soil p H showed a trend of decreased first and then increased with the planting years prolonging, the average annual soil p H fell 0.17 during the age of greenhouse in 1-7years, down to 7.4, and the soil p H was the average annual increase of 0.07 during the age of greenhouse in 7-22 years, up to 8.5. The contents of available Fe, Mn, Cu, Zn in the soil showed the accumulation trend with increasing planting years, and the average concentrations of available Fe, Cu, Zn were 0.65, 3.3, 3.8 times higher than that of the higest levels of soil fertility index in greenhouse of Hebei Province.2. The survey of conventional fertilization and nitrate leaching was carried out in the region with tomato greenhouses. The results showed that the total application rates of nitrogen(N), phosphorus(P2O5) and potassium(K2O) were 900 kg/hm2, 1020 kg/hm2,1300 kg/hm2, respectively during the whole growth period. The partitions of chemical N, P and K to the total were 40.1%、25.2%、35.2%, respectively. The results also showed that the amounts of nitrate leaching in greenhouse ranged at 37.9-212 kg/hm2 and the average soil NO3--N leaching amount was 139 kg/hm2. The percentage of nitrate leaching highest amount to the total N application highest rate was up to 20% and the percentage of average amount of nitrate leaching to average application rate of N was about 15.4%。3. Results of the plot experiment showed that the NO3--N was predominant species in leaching soil solution, accounting for 96% of total N, which indicated the nitrate leaching mainly happened in tomotao greenhouses. The amounts of leaching nitrate in the treatments of N2 and N2+DCD were reduced by 1.49% and 44.3% compared with threatments of N1 and N1+DCD, respectively. Moreover, the amounts of leaching nitrate in the N2+DCD treatment was reduced by 47.8% compared with N1 threatment, which suggested that the recommondary N amount could reduce nitrate leaching from soil profile of tomoto greenhouses.The N accumulation in 0-100 cm soil profile was determined after tomoto harvest.Theresults showed that the amounts of N accumulation in N1+DCD and N2+DCD treatments were 14.1% and 15.8% less than those of N1 and N2 treatments, respectively. It indicated that DCD application at the rate of 15% total N might decrease the level of nitrate accumulation in soil. The amount of N accumulation in soil of N2+DCD was reduced by 37.6% compared with N1 treatment.For the treatments of N1+DCD and N2+DCD, the yields of tomoto were 20.2% and2.37% higher, ammonia volatilization amounts were 16.16% and 21.68% lower, the soil N2 O emission were 44.42% and 77.62 lower than those of N1 and N2 treatments,respectively.In conclusion, application of 50% N of conventional fertilization and replacing 15%N of DCD in the period of tomato growth could decrease soil N accumulation by 37.6%,reduce soil nitrate leaching by 47.8%, decrease soil N2 O emissions by 93.04% and ammonia volatilization by 47.32%, and increase income by 15400 yuan/hm2, compared with conventional N fertilization, which can achieve the win-win situation of economic and environmental benefits. |
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