Impacts of application of calcium cyanamide and the consequent increase in soil pH on N 2 O emissions and soil bacterial community compositions

Calcium cyanamide, a component of lime-N, is gradually hydrolyzed into urea in soil and generates dicyandiamide, a nitrification inhibitor. Calcium cyanamide also increases soil pH. In this study, we determined the effects of calcium cyanamide application and the consequent increase in soil pH on N2O emissions and soil bacterial community composition. Five fertilizers (i.e., urea (U), cyanamide (CN), calcium cyanamide (CaCN), calcium hydroxide (Ca), and urea plus calcium hydroxide (CaU)) were applied using two methods (i.e., whole mixing and local placement in the mid layer) in a soil microcosm experiment. The control (CT) was left unfertilized. Compared with the U treatment, the CN, CaCN, and CaU treatments significantly suppressed N2O emissions. Fertilizer placement had less of an effect on N2O emissions. On day 7 after fertilizer application, soil bacterial alpha diversity indices were reduced in the CaCN, CN, and CaU treatments, and Planococcaceae was the dominant bacterial family. Compared with the bacterial communities in the other treatments, those in the CaCN, CN, and CaU treatments were predicted to contain fewer nitrification and denitrification genes. The soil bacterial community composition gradually shifted from that in CT as the soil pH increased. Our results suggest that, apart from the nitrification inhibitor effect of cyanamide, shaping the bacterial community compositions by the increase in soil pH under high urea concentrations could play an essential role in suppressing N2O emissions from soil.