Effect And Mechanisms Of Mineral Amendment On Carbon And Nitrogen Transformation During Livestock Manure Composting

Aerobic composting is widely accepted as a way to recycle organic waste harmlessly.While some disadvantages like greenhouse gas emission,nitrogen loss and low humification occur during the traditional composting,which restrict the development of composting technology.Therefore,it is essential to find a practical way to optimize composting process.Among of all methods,adding mineral additives has caused more attention due to their wide distribution and high availability.However,there is limited information about the role of mineral amendment in composting,so it is a prosperous field to search more mineral additives and explore their influence mechanism on aerobic compost.Based on these issues,different dosages of mineral additive[Tertiary-amine modified bentonite（TAMB）,Diatomite（DM）and Black tourmaline（TM）]were added into mixture of livestock manure and bulking agent for composting.The objectives of this manuscript were that:（1）to investigate the effect of TAMB,DM and TM on the greenhouse gas reduction,nitrogen conservation increasement and humification improvement;（2）to explore the mineral amendment with the greatest application potential in large-scale composting;and（3）to reveal the biological influence mechanism of mineral amendment on composting process,and verify its role on plant growth by pot experiment.And the details were as followed:（1）The application of TAMB,TM and DM into composting were beneficial for accelerating the O₂ diffusion in compost,and thus reduced the CH₄ emission by12.14%-32.78%,7.64%-43.95%and 14.92%-23.61%as well as N₂O by 35.23%-58.77%,69.79%-87.47%and 14.35%-73.23%.Meanwhile,TM played a key role in GHGs reduction by comparison with TAMB and DM,which was attributed to the different structure of these three mineral amendments.Besides,compared with the control,TAMB,TM and DM reduced the greenhouse gas equivalent value by 11.12%-39.32%,58.47%-76.13%and21.10%-72.31%,and thus reduced potential risks to ecological environment.（2）Compared with the control,adding TAMB,TM and DM into composting reduced the NH₃ emission by 5.63%-33.11%,22.88%-34.76%and 8.63%-35.29%,respectively.Through path analysis and the total effect of organic nitrogen components on the formation process of NH₄⁺-N,it found out that the degradation of amino acid nitrogen led to the accumulation of NH₄⁺-N during composting,while TM and DM promoted the transformation from NH₄⁺-N to ammonium nitrogen,amino acid nitrogen and hydrolysis undefined nitrogen,and thus reduced NH₃ emission.（3）The natural characteristics of TAMB,TM and DM including huge specific area and porosity could provide more oxygen and sites for degradation of degradable organic substances and the formation of humic substances.Compared with the control,the humic acid was improved by 11.71%-27.08%,5.71%-9.76%and 9.00%-18.42%,respectively.Besides,the UV-vis,Emission wavelength,Synchronous fluorescence spectrum,Fourier transform infrared spectroscopy and related parameters provided evidence for humification increasement in turn.（4）The mineral additives（TAMB,TM and DM）were regarded as effective additives to optimize the micro-environment of compost,thereby reducing greenhouse gas emissions,increasing nitrogen conservation and improving humification of compost.TM had the obvious effect on reducing greenhouse gas emission,TAMB significantly improved humification,while DM played a role in reducing ammonia emission.Furthermore,based on the comprehensive analysis of specific surface area,porosity,emission reduction and price,the maximum value in comprehensive score was DM,followed by TAMB and TM.These results indicated that DM had a prosperous field in composting technology among of three additives,and 10%DM was suggested.（5）Compared with the control,the DM amendment facilitated the relative abundance of Proteobacteria and Bacteroidetes.Besides,the addition of DM increased the abundance of carbohydrate metabolism and amino acid metabolism compared with the control,indicating that the addition of DM was conducive to promote the degradation of cellulose and hemicellulose as well as the synthesis of humic acid.Additionally,the higher methane metabolism abundance mainly occurred in the initial phase of the control,which was consistent with the profile of CH₄ emission.Furthermore,adding DM was favor for reducing the abundance of denitrifying genes（nar G,nos Z,nir S and nir K）,thus reduced N₂O emission.Combined with the pot experiments,it revealed that the application of compost into barren soil promoted the growth of lettuce（biomass,plant height and chlorophyll）,and the DM had no significant inhibitory effect on the growth of lettuce.In conclusion,the porous structure of mineral amendment could accelerate the oxygen diffusion,inhibit the activity of methanogens and decrease the abundance of denitrification genes,thereby reducing greenhouse gas emissions.Meanwhile,the negative charge on the surface of mineral amendment is beneficial for adsorbing NH₄⁺-N and promoting the transformation from NH₄⁺-N to amino acid nitrogen and hydrolyzed undefined nitrogen,and thus reduce NH₃ volatilization.Moreover,the large specific surface area of mineral amendment could provide more sites for microbial metabolisms,which is beneficial for improving the bacterial community succession and metabolic pathways,and thus promote the organic matter degradation and humification.Furthermore,compared to the TAMB and TM,DM has the greatest potential application in aerobic composting.