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

The excessive input of nitrogen (N) fertilizer and irrigation water to greenhouse vegetable production systems leads to N losses via nitrate (NO3--N) 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 NO3--N 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 Nha(-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 NO3--N, NH3 and N2O. The average NO3--N 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.