Optimization Of The Potential And Evaluation Of The Effect Of Synthetic Humic Acid To Activate Insoluble Inorganic Phosphorus Sources In Soils

Most of the inorganic phosphorus in soil exists in the form of insoluble minerals with poor effectiveness,which is a potential source of effective phosphorus in soil,and stimulating the activity of this part of phosphorus is of great importance to enhance soil phosphorus utilization.Exogenous application of phosphorus activators to improve soil inorganic phosphorus effectiveness has been a hot topic of academic research.Among many soil phosphorus activators,humic acid（HA）has received a lot of attention from scholars because of its functions of improving soil physical and chemical properties,carbon sequestration and promoting plant growth.Numerous studies have shown that HA activates soil ineffective phosphorus mainly through some interfacial behaviors in contact between the acidic functional groups in its structure and cations on the surface of soil colloids or minerals.However,the structural properties of humic acids in nature are limited by their sources and are extremely uncontrollable,which to some extent limits the function of humic acids in activating soil phosphorus.The structural properties of synthetic humic acids（SHLAs）can be controlled by changing the humification reaction conditions,thus optimizing their structure and function in a targeted manner.Compared with commercial humic acids（CHA）,SHLAs have greater potential for activation of soil phosphorus as well as promising applications.In view of this,this study optimized the acidic functional group content of synthetic humic acid materials using abiotic humification technology,explored the activation effect of SHLAs on insoluble inorganic soil phosphors,and evaluated their practical application potential.The study not only developed and verified the ecological and environmental functions of SHLAs,but also provided new ideas to improve soil phosphorus utilization and reduce the risk of environmental phosphorus pollution.The main research findings of the paper are as follows:（1）The concentration ratio（w/v）between the precursor（dissolved organic carbon）and the catalyst of the humic acid reaction significantly influenced the yield,darkness,average molecular weight and acidic functional groups of the synthetic humic acid;when the input ratio was 1:1,the carboxyl group and the total acidity content of the synthetic humic acid were the highest,5.08±0.11（mmol/g）and 11.53±0.08（mmol/g）,which were 2.9 and 2.8 times higher than the carboxyl group and total acidity in CHA,and their yields met the requirements of practical applications,so this reaction condition was chosen as the best solution to enhance the activation potential of humic acid materials for soil inorganic phosphorus。（2）The optimized synthetic humic acid has certain activation ability for dicalcium phosphate（Ca₂-P）,octacalcium phosphate（Ca₈-P）,calcium phosphate(Ca₁₀-P)and aluminum phosphate（Al-P）;meanwhile,its activation ability for Ca₂-P,Ca₈-P and Al-P is significantly stronger than that of commercial humic acid,which verifies the feasibility of using abiotic humification technology to optimize the activation ability of humic acid-based materials for insoluble inorganic phosphorus sources.（3）The results of soil simulation experiments showed that the addition of synthetic humic acid enhanced the organic matter content of soil,and the medium（1.0%）and high（2.0%）concentrations（w/w）of synthetic humic acid significantly enhanced the content of soil effective phosphorus and loose easily exchangeable inorganic phosphorus;synthetic humic acid promoted the conversion of Ca₂-P,Ca₈-P and Al-P fractions to the effective form,and the activation effect increased with the concentration of synthetic humic acid The activation effect increased with the increase of synthetic humic acid concentration;the activation ability of synthetic humic acid to Fe-P and Ca₁₀-P fractions was limited;it proved that the activation ability of synthetic humic acid to insoluble inorganic phosphorus sources in soil was better than that of commercial humic acid.Therefore,synthetic humic acid has better research value and application prospect than commercial humic acid in enhancing the effectiveness of soil inorganic phosphorus.