Research Of Nitrogen Transformation And Greenhouse Gas Emissions In Erhai Basin During Dairy Manure Composting

Composting is an environmentally friendly technology for treating livestock manure by transforming organic matter into more stable and nutritional fertilizer.The composting method is an important factor influencing maturity,and nitrogen loss and conservation from the composting process while nitrogen loss may reduce the agronomic value and damage the ecosystems.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 contributes to environmental problems such as global warming,which reduces the environmental benefits of composting.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 four composting methods during composting have received little attention.Maturity indexes such as temperature and germination index were determined,leachate and compost and continuous measurements of gaseous emissions（N₂O and CH₄）were taken during the 64 d experiment.These results will assist in 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 indexes were monitored in four composting mixtures in Dali prefecture,Yunnan province.Gas samples were taken at various stages of composting from December 2015 to February 2016 over 64 days.Therefore,the purpose of this research was to investigate the effects of composting methods（farmer compost,anaerobic compost,mixed compost and aerobic compost）on maturity,nitrogen loss and conservation during dairy manure composting,and the greenhouse gas and ammonia emissions.The results are as follows:（1）Effects of composting methods on maturity during dairy manure compostingThe temperature of aerobic compost rose rapidly higher than 50℃,which has the longest thermophilic stage（>50℃）.The value of pH fluctuated between 7.5⁸.5 during composting,maximum pH occurred in aerobic compost,and mixed compost followed.The EC value became relatively stable at the end of composting.Mixed compost had the highest EC value,and aerobic compost lowest.Except for farmer compost（65.9%）,others reached the required maturity standard（>80%）.The results showed that the aerobic compost resulted in the most desirable maturity.（2）Effects of composting methods on nitrogen loss and conservation during dairy manure compostingThe results showed that nitrogen loss at 27.9%、27.0%、30.0%and 25.1%of initial nitrogen occurred in the farmer compost,anaerobic compost,mixed compost and aerobic compost,respectively.Compared with N₂O and leachate,NH₃ emission was the main contributor to nitrogen loss.Nitrogen loss of aerobic compost as NH₃ emission comprised 22.5%of initial nitrogen,mixed compost was lower（16.6%）,while 7.5%in anaerobic compost.Cumulative N loss via N₂O emissions varied depending on the composting methods,which accounted for 0.06%⁰.11%of initial nitrogen.Leachate was also an important way of nitrogen loss and about 1.5%¹2.0%of initial nitrogen was lost as it.Farmer compost effectively increased it for no covering.Nitrogen lost in other forms accounted for1.0%¹0.2%and aerobic compost caused lowest nitrogen loss in other forms,while anaerobic compost had the highest.These results clearly show that aerobic compost is effective for reducing nitrogen loss and promoting maturity.（3）Effects of composting methods on greenhouse gas emissions during dairy manure compostingThe results showed that the aerobic compost effectively reduced CH₄ and N₂O emissions.However,this composting method did not reduce CO₂ and NH₃ emissions from the cumulative gaseous emissions.Under covering composting conditions,CH₄ emissions increased by 48.7%,and NH₃ emissions decreased by 8.0%compared with the results for farmer compost;however,N₂O emissions from covering composting conditions were similar to those from farmer compost,which resulted from covering with a plastic film.Although the covering-turning compost improved the maturity of the final compost,this method also featured increased emissions of CH₄,CO₂,and NH₃.Throughout the study period,aerobic compost released the lowest amounts of total greenhouse gas（CH₄ and N₂O）emissions（18.0 kg CO₂-eq/t）,followed by farmer compost（25.6 kg CO₂-eq/t）,anaerobic compost（32.9 kg CO₂-eq/t）,and mixed compost（38.1 kg CO₂-eq/t）.The total greenhouse gas（CH₄ and N₂O）emissions of the anaerobic compost and mixed compost were 1.8 and 2.4 times as high as that of aerobic compost at time of maturity,respectively.The greenhouse gas and ammonia emissions varied substantially with time and 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,aerobic compost showed the greatest potential to mitigate the overall greenhouse effect and give greater maturity than the other three composting methods.Moreover,the lower cost and operational convenience of aerobic compost could allow these methods to be easily put into practice.Among the four composting methods,aerobic compost was considered to be a superior composting method,which should be promoted among farmers.（4）Effects of biochar addition on nitrogen loss and greenhouse gas emissions during dairy manure compostingBiochar in the composting process could prolong the period of high temperature,reduce CH₄ and NH₃ emissions,but did not reduce CO₂ and N₂O emissions.Compared with other compost,biochar compost could effectively reduce nitrogen loss（12%）,the total greenhouse gas effect（14.1 kg/t）were44.1%and 35.5%of anaerobic and aerobic compost.