The Influence Mechanism Of Different Additives On The Humification Of Aerobic Composting Of Sand Containing Cow Manure

In the western region of China,sand-based bedding is widely available and is the preferred bedding for dairy farming.However,due to the high sand content and low porosity,organic matter and nutrient content of cattle manure,there are problems such as difficulties in achieving harmlessness as well as low humification when aerobic composting is carried out,and additives such as conditioners and modifiers are needed for improvement.However,it is not clear about the efficient additives for aerobic composting of cattle manure containing sand and their mechanism of action on the effect of humification.Therefore,this article uses cow manure with different sand contents as the main raw material,corn straw,rice husk,grape branches,mushroom residue as conditioning agents,and bacterial agents,biochar,potato residue,soybean residue were added as modifiers,batch composting experiments were conducted in a static forced-air reactor to study the effects of these additives on the harmlessness index,organic matter,nutrient content,carbon and nitrogen conversion,extracellular enzymes and humification during aerobic composting of sand-containing cow manure.The main research conclusions are as follows:(1)Effect of different additives on the quality of aerobic composting of cattle manure with different sand content:it was difficult to warm up the manure with 77%sand content when composted alone or with the addition of bacterial agents,and although the addition of conditioning agents such as corn straw,rice husk and grape sticks all helped to warm up the pile,it was difficult to rise above 50℃ and lasted for a short time.At the end of composting,none of the groups reached harmlessness.The addition of corn straw,grape sticks and mushroom residue to the cow manure compost with 27%sand content could make the compost reach harmlessness,and the total nutrient content(3.9%)was significantly higher with the addition of corn straw than the remaining two groups,and the huminic acid content was elevated by 20.32%to 23.77%,but all groups needed to add more organic fertilizer returns to regulate the moisture content.In the combined compost of cow manure with 47%sand content and corn straw and mushroom residue,the addition of bacterial agents,biochar and soybean residue extended the duration of the high temperature period of composting by 4,6 and 3 days,respectively.At the end of composting,all groups reached harmless and total nutrient content higher than 4%except for the addition of potato residue.The total nutrient content and huminic acid content of added bacterial agents,biochar,and soybean residue increased by 38.46%,52.66%,87.77%,and 12.59%,13.98%,and 11.92%,respectively,and the reduction of fulvic acid content and HA/FA were significantly greater than the control,both of which favored the conversion of fulvic acid to huminic acid.The cow manure with 47%sand content was suitable for aerobic composting.(2)Effects of different modifiers on carbon and nitrogen conversion and humification process of aerobic compost containing sandy cow manure:On the basis of combined composting of cow manure with 47%sand content and corn straw and mushroom residue,carbon and nitrogen losses were reduced by 8.38%,13.62%and 44.84%,62.75%for the addition of bacterial agents and biochar,respectively,and carbon losses were reduced by 14.67%but increased by 67.10%for the addition of soybean residue.From the compost UV-Vis data,the humification rate of potato residue was reduced,and the humification effect of sand cow manure compost after adding bacterial agents,biochar and soybean residue was improved,and the values of SUVA254 and SUVA280 increased by 4.07%,10.16%,6.91%,2.84%,11.37%and 9.00%,respectively.At the end of composting,the E250/E365 value of the treatment group added with soybean residue was the lowest,the A240～400 value was the highest,and the DOM had the largest relative molecular weight and the highest degree of humification.It can be seen from the 3D-EEM spectral data of composting that at the end of composting,the PⅤ,n/PⅢ,n values of added bacterial agents,biochar and soybean residue were 4.04%,7.07%and 7.07%higher than those of the control,respectively.The addition of bacterial agents,biochar and soybean residue could improve the humification degree and humus amount of sand containing cattle manure compost.(3)Effect of different modifiers on the activity of extracellular enzymes in aerobic composting of cattle manure containing sand:On the basis of combined composting of cow manure with 47%sand content and corn straw and mushroom residue,the addition of soybean residue significantly increased the activity of LAP,the addition of biochar increased the activity of PPO,and the addition of potato residue and soybean residue significantly increased the activity of PER.On day 0,compared to the control,the addition of bacterial agents reduced the N and P limitations on microorganisms;The addition of biochar reduced the P restriction on microorganisms.On days 7-12,compared to the control group,the addition of bacterial agents,biochar,and soybean residue reduced the N and P restrictions on microorganisms,indicating that the environment of the composting system was improved and the nutrient acquisition ability of microorganisms was enhanced.The treatment group added with potato residue had more severe C and N restrictions on microorganisms,which persisted until the end of composting.The RDA results show that without the addition of exogenous precursor substances,BG:AP is the main factor affecting the changes in humic acid composition.Humic acid is mainly formed through the decomposition of lignocellulose,and when microorganisms in the pile are restricted by N and P,extracellular enzymes involved in the N and P cycle will also have a significant impact on humic acid production.When adding exogenous precursors,LAP,AP and PPO are the main factors affecting the formation of humic acid components.Humic acid is mainly formed through the condensation of protein like and lignocellulose like substances.TK,PPO,EC,MC,TP,PER,BG are the main factors affecting the changes in humic acid composition during the composting process of sandy cow manure.Humic acid formation in compost is driven by environmental factors,extracellular enzymes and nutrient content are important factors that promote humic acid formation.In conclusion,the composting of cow manure with 47%sand content with the least amount of additives added in the composting process can meet the standard requirements of organic matter content,total nutrient content,seed germination index,and heavy metal content in Organic Fertilizer(NY 525-2021).Corn straw is the best conditioner,and modifiers such as bacterial agents,biochar and soybean residue can promote the process of harmless and humification of aerobic compost containing sandy cow manure.Humic acid formation in compost is driven by environmental factors and promoted by a combination of microbial extracellular enzymes and nutrients.