Effects of dicyandiamide (DCD) on nitrate leaching, gaseous emissions of ammonia and nitrous oxide in a greenhouse vegetable production system in northern China

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Abstract
The excessive input of nitrogen (N) fertilizer and irrigation water to greenhouse vegetable production systems leads to N losses via nitrate ( ) leaching, ammonia (NH3) volatilization and nitrous oxide (N2O) emissions. Besides management of N fertilizer and irrigation inputs, the addition of the nitrification inhibitor dicyandiamide (DCD) has also been shown to mitigate N losses from soils. A greenhouse experiment was set up to identify the effects of combining DCD with recommended N and irrigation management on leaching, NH3 volatilization and N2O emissions under intensive vegetable production of tomatoes (Lycopersicon esculentum Mill.). The five treatments were: (A) control + TMI (traditional managed irrigation); (B) TN (traditional N rate applied at 410 kg N ha−1) + TMI; (C) RN (recommended N rate applied at 210 kg N ha−1) + DCD (21 kg ha−1) + OMI (optimum managed irrigation); (D) 80%RN (N rate applied at 80% of the recommended N rate, 168 kg N ha−1) + DCD (16.8 kg ha−1) + OMI; and (E) 120%RN (N rate applied at 120% of the recommend N rate, 252 kg N ha−1) + DCD (25.2 kg ha−1) + OMI. DCD was applied at the rate of 10% of the N application rate. The results showed that the recommended N rate and irrigation with the addition of DCD (RN + DCD + OMI, 80%RN + DCD + OMI, and 120%RN + DCD + OMI) can significantly reduce N loss as , NH3 and N2O. The average concentrations in the top soil depth were decreased by 49.34–55.54%, total NH3 volatilization were decreased by 20.61–41.51%, and N2O emission factors were reduced by 84.07–96.19%. In addition, the utilization efficiency of N was enhanced. However, there was no significant effect of the recommended N rate and DCD plus optimum managed irrigation on tomato yield. Overall, these results suggest that applying 80%RN + DCD + OMI may provide a practicable option for both mitigating N losses and improving utilization efficiency of N under intensive greenhouse vegetable production systems.

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