Effect Of Dicyandiamide On Process And Denitrification Functional Genes During Agricultural Waste Composting

Composting is one of the effective biotechnologies to dispose agricultural waste. Through the composting of rice straw to produce organic fertilizer is the effective means to solve the problem of excess straw. Nitrogen loss usually occurs during composting of wastes. Denitrification is one of the important reasons for the nitrogen loss in composting process. Compost additives are often used to control nitrogen loss during composting. Most researches about controlling nitrogen loss focus on its results,but seldom pay attention to the dynamic changes of the microbial nitrogen transformation. Thus revealing the microbiology mechanism of nitrogen transformation in composting process is important for developing new efficient technology. Nitrification inhibitors are compounds which are widely used in the soil to improve the utilization efficiency of nitrogen fertilizer because of regulation of nitrogen transformation. Recently researchers tried to use nitrification inhibitors in compost as a measure to regulate nitrogen transformation and reduce nitrogen loss. However, how the denitrifying communities and composting process are affected by the application of nitrification inhibitors is poorly understood.Static aerobic composts based on straw were added with nitrification inhibitor?Dicyandiamide?. Two tests with and without nitrification inhibitor were set up respectively. The variation trends in p H, NH+ 4-N,NO-3-N and WSC concentrations during composting were analyzed, and the abundance of the denitrification functional genes?nir K, nir S and nos Z? were investigated using the real-time polymerase chain reaction?real-time PCR?.The results showed that the addition of nitrification inhibitor had a significant effect on nitrogen transformation in composting. The p H, NH₄⁺-N, and NO-3-N were influenced by nitrification inhibitor significantly?p<0.001?, but it has no significant effect on the degradation of WSC during composting. Nitrification inhibitor had a most significant inhibition on nir K gene, it maintained at a low level throughout the composting process in DCD treatment and significantly lower than the control group. The nir S and nos Z genes in two samples reached a peak at different times and changed significantly over time. Redundancy analysis?RDA? suggested that DCD was the significant factor in effecting the nir K gene, WSC and NO₃^--N had the most impacts on the abundances of the three genes?p < 0.05?, and it indicated that characteristics of compost sample between two groups were the major cause for changes of denitrification genes nir S and nos Z abundance.