Effective mitigation of nitrate leaching and nitrous oxide emissions in intensive vegetable production systems using a nitrification inhibitor, dicyandiamide

Vegetable production is one of the most intensive agricultural systems with high rates of nitrogen (N) fertilizer use and irrigation, conditions conducive for nitrate (NO (3) (-) ) leaching, and nitrous oxide (N2O) emissions. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO (3) (-) leaching and N2O emissions in vegetable production systems. Twenty-four undisturbed soil monolith lysimeters (610 mm in diameter; 700 mm in depth; surface area, 0.29 m(2)) with two different soils, Huangzongrang (alfisol) and Chaotu (fluvisols), were collected and installed in a field lysimeter facility in Central China under irrigated vegetable production conditions. Urea fertilizer was applied at 650 kg N ha(-1), and DCD was applied at 10 kg ha(-1) to the lysimeters planted with three kinds of vegetables (capsicum, Capsicum annuum L.; amaranth, Amaranthus mangostanus L.; radish, Raphanus sativus L.). The results showed that DCD reduced NO (3) (-) leaching by 58.5% and 36.2% and N2O emissions factor by 83.8% and 72.7% in the two soils. The average NO (3) (-) -N concentration in the drainage water was decreased from 4.9 mg N L-1 to 2.3 mg N L-1 and from 4.4 mg N L-1 to 3.3 mg N L-1, in the Huangzongrang and Chaotu soils, respectively. In addition to the environmental benefits, the use of DCD also increased the yields of capsicum and radish in alfisol soil significantly (P < 0.01); only the amaranth yield in fluvisol soil was declined (P < 0.01), and the other vegetables yields were not affected. Total N concentrations of the three vegetables were increased significantly (P < 0.01) with the application of DCD with urea compared with urea alone. These results showed that the nitrification inhibitor DCD has the potential to significantly reduce NO (3) (-) leaching and N2O emissions and to make vegetable farming more environmentally friendly. These results demonstrated that the use of the nitrification inhibitor DCD can significantly reduce NO (3) (-) leaching, N2O emissions, and the average NO (3) (-) -N concentration in the drainage water, while increasing the fertilizer N efficiency in the vegetable production system.