Abstract:
Composting is an environmentally friendly technology for treating livestock manure by transforming organic matter into more stable and nutritional fertilizer. However, composting is also a significant source of CH4, CO2, N2O and NH3 gases if proper composting methods are not used. The production of these gases not only reduces the agricultural value of the final compost but also aggravates some environmental problems such as global warming, which reduces the environmental benefits of composting. Four types of composting methods are used extensively, namely farmer compost (FC), covering compost (CC), covering-turning compost (CTC) and covering and aeration-turning compost (CATC). Concerns about climate change have increased the demand for strategies to minimize greenhouse gas and ammonia emissions. However, the greenhouse gas and ammonia emissions from the 4 composting methods during composting have received little attention. The purpose of this study was to analyze the greenhouse gas and ammonia emissions from the composting of dairy manure with these 4 types of composting methods. These results will assist the identification of better composting methods with the potential to mitigate greenhouse gas and ammonia emissions. The evolution of CH4, CO2, N2O and NH3 and maturity index were monitored in 4 composting mixtures in Dali Prefecture, Yunnan Province. Gas samples were taken at various stages of composting from December 2015 to February 2016, and the period was over 64 days. The results showed that the CATC resulted in the most desirable maturity, and effectively reduced CH4 and N2O emissions. However, this composting method did not reduce CO2 and NH3 emissions from the cumulative gaseous emissions. Under the CC conditions, CH4 emissions increased by 48.7% compared with the FC; however, N2O and NH3 emissions from the CC were similar to the FC, which resulted from covering with a plastic film. Although the CTC improved the maturity of the final compost, this method was also featured with the increased emissions of CH4, CO2, and NH3. Throughout the study period, the CATC released the lowest amount of total greenhouse gas (CH4 and N2O) (18.0 kg/t), followed by the FC (25.6 kg/t), CC (32.9 kg/t), and CTC (38.1 kg/t). The total greenhouse gas (CH4 and N2O) emissions of the CC and CTC were 1.8 and 2.1 times as high as that of CATC at the time of maturity, respectively. The greenhouse gas and ammonia emissions varied substantially with time and were significantly correlated with temperature. The pH values of the compost could significantly affect the emissions of N2O and NH3, which indicated a potential way to mitigate greenhouse gas and ammonia emissions through proper compost management. Compared with other composting methods, the CATC showed the greatest potential to mitigate the overall greenhouse effect, and a greater maturity than the other 3 composting methods. Moreover, the lower cost and operational convenience of CATC could allow this method to be easily put into practice. Among the 4 composting methods, covering and aeration-turning compost (CATC) is considered to be a superior composting method, which should be promoted among farmers.