Effects of Dicyandiamide on Tomato Growth and Nitrogen Leaching from Soil in Intensive Greenhouse Under Different Irrigation and Nitrogen Managements

Effects of a nitrification inhibitor,dicyandiamide(DCD) on the tomato growth and nitrogen leaching from soil in intensive greenhouse under different irrigation and nitrogen managements were studied by using a field experiment.The results showed that the combination of recommended nitrogen and irrigation with the addition of DCD could significantly inhibit the decrease of the NH+4-N contents in the soil,and reduce nitrogen loss as NO-3-N.Comparing with the traditional management of nitrogen and irrigation,the combination of recommended nitrogen and irrigation with the addition of DCD(W2N2+DCD,W2N3+DCD and W2N4+DCD) could improve the average utilization efficiency of nitrogen from 13.84% to 22.45%.In addition,the average NO-3-N content in the top soil depth(0-10 cm) was decreased by 49.34%~55.54%,the NO-3-N contents in the 0-30 cm and 30-120 cm soil profiles were also reduced by 35.21%~64.88% and 61.08%~72.00%,respectively.Meanwhile,the combination of recommended nitrogen and irrigation with the addition of DCD could also significantly decrease the NO-3-N contents in tomato fruit,and improve the quality of tomato fruit.The NO-3-N content in tomato fruit was decreased by 51.94%~62.82%,but the yield of tomato were not significantly affected by the combination of recommended nitrogen and irrigation with the addition of DCD.During the tomato growth,the nitrogen input and amount of irrigation in W2N2+DCD treatment were decreased by 59.02% and 29.80% in comparison with the traditional management of nitrogen and irrigation.However,comparing with the traditional management of nitrogen and irrigation,W2N2+DCD could reduce the NO-3-N accumulation in the top soil depth(0-10 cm) by 54.01%,and reduce the NO-3-N accumulation in the 0-120 cm soil profiles by 58.32%,72.80%,63.23% and 52.60% during the early,middle,late fruit stage and after-harvest stage,respectively.Furthermore,the utilization efficiency of nitrogen was improved to 25.49%,and the NO-3-N content in tomato fruit was decreased by 59.81%.Overall,these results suggested that the W2N2+DCD could offer the best economic benefit and environmental benefit.