Transformation And Rugulation On Phosphorus Fractions During Livestock Manure Composting

Organic fertilizer replaces chemical fertilizer,is an important way to alleviate agricultural non-point pollution,and also an effective method to increase available phosphorus in arable soil.Therefore,how to convert non-available phosphorus in livestock manure into available phosphorus is an urgent matter to popularize organic fertilizer.Aiming at the serious problem associated with agricultural non-point pollution,we selected microorganisms,organic matter,heavy metals and antibiotic as primary influencing factors.According to the substantial principle of aerobic composting,we studied the redistribution characteristic on phosphorus fractions to increase available phosphorus during the composting process,screened out the specific microbial communities that affect the phosphorus availability,constructed the coupling correlation between the decomposition and humification process of organic matter as well as the transformation process among phosphorus fractions,and identified the potential microbial carries of phosphorus functional genes as well as the stability of carbon-phosphorus organic compounds.These results could provide theoretical direction for the ‘targeted’ research and development on the composting technology.Meanwhile,we took the dosage and particle-size of exogenous additives as the pointcut to explore the effectiveness and mechanism of biochar and medical stone in regulating phosphorus availability during the composting process,so as to optimize the composting scheme.The main conclusions are summarized as follows:(1)TP content in composting mixtures showed an increasing tendency,and ranged from 18569.91 mg/kg to 27619.46 mg/kg;while Ex-P decreased by 6.70%-15.69%.Org-P was the primary phosphorus fraction,which accounted for 48.62%-83.18% of TP content,followed by Ex-P(6.38%-28.97%)and Ca-P(12.95%-28.64%),while the content of Fe-P,Al-P and O-P was low.During the temperature-heating and thermophilic phases,Ca-P and Org-P were converted into Ex-P.Thus,it was a key period to increase the phosphorus availability during the composting process.During the temperature-colling and maturation phases,the transformation of Ex-P to Org-P reduced the phosphorus availability.(2)During the temperature-heating and thermophilic phases,Firmicutes was the primary bacterial phylum.During the temperature-cooling and maturation phases,Proteobacteria,Bacteroidota and Actinobacteria gradually replaced Firmicutes as the dominant bacteria phylum.Ascomycota,Basidiomycota and Neocallimastigomycota were abundant in the fungal community.During the composting process,Ascomycota and Neocallimastigomycota gradually decreased with the composting time,while Basidiomycota basically remained steady.Kurthia in genus-level,belonged to Firmicutes in phylum-level in bacterial communities,and Aspergillus,Phaeosphaeriaceae,Penicillium and Hypocreales in genus-level,affiliated to Ascomycota in phylum-level in fungal communities,were potential microbial carries of phosphorus functional genes.(3)During the composting process,unstable organic carbon,including sugars(OH)and aliphatic(C-H),gradually converted into stable organic carbon,such as aromatic(C=C),asymmetric(C-O)and carboxyl(C-O-H)substances.Tyrosine acid-like and tryptophan acid-like components in dissolved organic carbon were preferentially decomposed.Fulvic acid-like and soluble microbial product components in dissolved organic carbon were gradually converted into humic acid-like substances.Tyrosine acid-like and tryptophan-like substances could promote Ca-P dissolution.I-P was converted into Org-P during the formation process of humic acid-like substances.(4)Copper and tetracycline-amended treatments reduced the content of available phosphorus by 4.71%-9.19% and 7.75%-10.78%,respectively.Meanwhile,Copperamended treatments inhibited the transformation of Org-P to I-P.Both copper and tetracycline reduced phosphorus availability during the composting process,through decreasing the abundance in microbial phylum that carries phosphorus functional genes.When it came to bacteria,copper and tetracycline-amended treatments reduced the abundance in phosphorus functional genes,which were carried by Actinomadura,Weissella,Kurthia and Aerococcus in genus-level,affiliated to Firmicutes in phylumlevel,and Luteimonas in genus-level,affiliated to Proteobacteria in phylum-level,as well as Gulbibacter in genus-level,affiliated to Bacteroidota in phylum-level.With respect to fungi,copper and tetracycline-amended treatments reduced the abundance in phosphorus functional genes,which were carried by Debaryomyces and Cladosporium in genus-level,affiliated to Ascomycota in phylum-level,as well as Symmetrospora,Occultifur and Coprinopsis in genus-level,affiliated to Basidiomycota in phylum-level.(5)Compared to the control treatment without biochar and medical stone,5% and10% biochar-amended treatments increased phosphorus availability by 9.63% and10.18%,respectively.Medical stone-amended treatments with particle size of below0.1 mm and(3-5)mm,increased phosphorus availability by 8.32% and 6.35%,respectively.Biochar-amended treatments promoted the dissolution of nonvalent inorganic phosphorus and the mineralization of organic phosphorus,through improving the activity of phosphorus-solubilization microbial communities,thus,increased the phosphorus availability during the composting process.Medical stone-amended treatments accelerated the decomposition of unstable organic matter,by increasing the pore structure of composting materials,thereby increasing the phosphorus availability during the composting process.Biochar(10%)and medical stone(3-5 mm)showed the considerable composting quality and phosphorus availability.