Effect of Biochar Application on the Efficacy of the Nitrification Inhibitor Dicyandiamide in Soils

A series of laboratory incubation experiments was conducted to evaluate the effect of biochar application on the efficacy of the nitrification inhibitor (NI) dicyandiamide (DCD) in Cambisol (pH 7.14) and Latosol (pH 4.83). The feedstocks (eucalyptus wood, coconut coir, and rice straw), pyrolysis temperatures (350, 500, and 650 ˚C), and application rates (0.5, 1.0, 2.5, and 5.0% of 200 g soil) were identified as influential factors. The results showed that biochar could significantly reduce the effectiveness of DCD on nitrification inhibition. Biochar produced from eucalyptus wood with a large surface area (426.4 m2 g−1) had the strongest ability to reduce the inhibitory effect of DCD in nearly neutral Cambisol, while biochar from rice straw with a high pH had the greatest influence on acidic Latosol. Increasing pyrolysis temperature and application rates can strengthen the ability of biochar to reduce the inhibitory effect of DCD. Generally, the decrease of the DCD nitrification inhibitory effect on nearly neutral soil was controlled by the surface area of the applied biochar; meanwhile, the rise of soil pH caused by biochar application was also an important influencing factor in acid soil.