Effects Of Different Amendments On Greenhouse Gas Emissions And Nitrogen Transformation In Deer Manure Composting

Composting achieves biodegradation and recycling of organic waste,meanwhile emits greenhouse gases?GHGs,Greenhouse Gases?and ammonia into the environment,causing nitrogen losses and environmental problems such as global warming.The addition of composting amendments can alleviate the adverse effects,and the characteristics and mechanisms of interaction between different amendments and substrates are different.In order to clarify the specific influence of the amendments on the composting process and its mechanism,monitoring of the composting indicators under different conditions was carried out,which provided a reference for finding the most suitable amendment for deer manure-straw co-composting.Deer manure and corn stalks were used as composting substrate,biochar and zeolite were used as amendments with four treatment groups and performed with initial C/N ratio of 30,initial moisture content of 60%and total weight of 4 kg.Basic physical and chemical indicators,different forms of nitrogen contents,greenhouses gas emissions and ammonia emissions were continuously monitored.Dynamic changes of enzyme activities,detrended correspondence analysis,redundance analysis methodology,scanning electron microscope?SEM?and energy dispersive spectrometer?EDS?explain the mechanisms of greenhouse gas emissions and nitrogen transformation during composting.The results show that,the highest stack temperature?58.1°C?appears in the zeolite treatment group on 7^th day,and this group also meets the hygiene requirements of the U.S.EPA and Ministry of Health,PRC,zeolite has the best effect on the harmlessness of compost products;the ratio of C/N ratio to innitial C/N ration?T value?inbiochar-zeolite treatment group is 0.57 on the 29th day,which drops below 0.6 firstly,indicating that the biochar-zeolite amendment has the greatest promoting effect on compost maturity.Biochar-zeolite amendment increases the moisture from 43.64%to 63.75%,significantly promotes the water retention of deer manure-straw co-composting?t test,P=0.005<0.05?;biochar increases the TOC degradation rate by 35.55%,it has the best effect on promoting organic matter decomposition and comprehensive utilization of carbon and nitrogen nutrients.The results of gas emission characteristics show that,biochar-zeolite amendment reduces CH₄ emissions by 28.15%and 58.84%on 6^th day and 8^th day respectively,it has inhibitory effect on CH4 emissions at the beginning of heating period;biochar reduces the CO2 cumulative emissions by 25.10%,indicating that it has the best effect on CO2 emission reduction;while zeolite amendment reduces N2O cumulative emissions by 28.02%through inhibiting nitrification and denitrification processes during the cooling period.Moreover,zeolite and biochar reduce NH3 cumulative emissions due to their characteristics of reducing conductivity and improving oxygen supply.biochar amendment finally reduces global warming potential by8.17%,achieves the inhibition of global warming caused by straw-deer manure composting,and controlling CH₄ emission is the key to weakening the greenhouse effect.As for nitrogen transformation and nitrogen losses,the amount of NO₂^--N increase in biochar treatment group accounts for 60.93%of the total nitrogen increase,indicating that biochar makes this composting system change from ammoniation-dominated composting to nitrification-dominated composting;while the amount of total kjeldahl nitrogen increase in zeolite and biochar-zeolite treatment groups accounts for 57.53%and 74.60%of the total nitrogen increase respectively,suggesting that zeolite and biochar-zeolite amendment make ammoniation reaction to dominate composting;and these three amendments alternately play a role in controlling nitrogen loss during different composting stages,nitrogen loss from NH₃release accounts for 84.30%of the total nitrogen loss,which is the key factor to reduce nitrogen loss during deer-straw co-composting.There are differences in the mechanisms of controlling gas emissions and nitrogen losses by these amendments:biochar-zeolite amendment improves the urease activity?t test,P=0.028<0.05?,and its NH₃ emission mainly comes from the hydrolysis of urea,rather than the conversion of ammonia nitrogen.Scanning electron images show that biochar maintains a stable open pore structure;while zeolite has a strong adsorption capacity for compost products;the percentage of oxygen atoms in zeolite particles decreased from 66.02%to 46.71%after composting,and the denitrification reaction is still carried out inside the heap.The results of the redundancy analysis show that biochar has a certain contribution to the activity of urease;zeolite amendment enhances the effect of carbon on C/N ratio;biochar-zeolite amendment improves the carbon and nitrogen balance of the heap to a certain extent,and makes a relatively stable change process in the early stage of composting.On the whole,based on the good pore structure and adsorption capacity of biochar and zeolite,biochar-zeolite amendment advances the maturity process,and controls CH₄ emissions;and the single amendment of biochar and zeolite promote the detoxification of compost,reduce NH₃ and N₂O emissions,and controls nitrogen losses and global warming potential during deer-stalk co-composting.