Effects of different C/N ratios on greenhouse gases emissions and carbon and nitrogen conversion during composting of cultural materials of A.bisporus

Abstract: In fermentation process of culture materials of A. bisporus, there are problems such as low conversion efficiency of organic matter, and a lot of greenhouse gas emissions, which not only influence the quality of composting products, but also cause the pollution in the surrounding environment. Therefore, greenhouse gas emissions have become an important issue in the production processes of A. bisporus. In recent years, most researches have focused on the conversion efficiency of organic matter and dynamic changes of microbial community during the composting, while the regularity of greenhouse gas emissions is still poorly understood. To understand the regularity of the greenhouse gas emissions and to explore the relationship between greenhouse gas emissions and the conversion of organic matter, an experiment was conducted to quantify the greenhouse gase emissions (including CO2, CH4 and N2O), and meanwhile to determine the total carbon and nitrogen contents during the composting with different ratios of C/N. The fermentation experiment was conducted in a reaction chamber, and the rice straw and cow dung were used as raw materials. There were 4 treatments with the C/N ratios of 28:1, 33:1, 38:1 and 43:1, and each treatment had 3 replications. Fermentation lasted for 18 d, and the turning was done on the 7th and 14th day during the composting. The results showed that during the composting with the C/N ratios of 28, 33, 38 and 43, the average emission rates of CO2 were 489.47, 400.70, 362.31 and 357.22 mg/(kg?h), the average emission rates of CH4 were relatively lower and ranged from 0.02 to 0.06 mg/(kg?h), and the average emission rates of N2O were 0.03, 0.02, 0.01 and 0.01 mg/(kg?h). The cumulative amount of CO2 emissions was the largest, while the cumulative amounts of CH4, N2O and NH3 emissions were relatively lower during the composting with different C/N ratios. The cumulative amounts of CO2, N2O and NH3 emissions were increased with the increasing of the ratio of C/N. The lost carbon amounts in forms of gases were 46.16, 37.44, 33.04 and 31.76 g/kg and the lost nitrogen amounts in forms of gases were 4.72, 3.49, 1.76 and 1.65 mg/kg with the C/N ratios of 28, 33, 38 and 43, respectively. In addition, the degradation rate of organic matter with the C/N ratio of 33 was the highest among all treatments. At the end of composting, the lost carbon amounts were 36.55%, 45.5%, 37.22% and 32.71%, and the lost nitrogen amounts were 5.41%, 13.84%, 7.59% and 16.33% respectively with the C/N ratios of 28, 33, 38 and 43. The relative nitrogen content was concentrated with organic matter degradation, and continuously increased during the composting process. The C/N ratios of 33 and 38 had the highest fruit body yield and absolute biological efficiency of A.bisporus, and there were no significant difference between these 2 treatments. Considering both greenhouse gas emissions and culture materials quality, C/N = 38 was the better treatment, which not only had the high quality, but also could reduce the emissions of greenhouse gases. Besides, greenhouse gas emissions mainly occurred in high temperature periods, and turning timely could also reduce the emissions of greenhouse gases. The results can provide a theoretical basis to further explore how to reduce the greenhouse gas emissions during the fermentation process of cultivated material of A.bisporus.