Effects Of Different Treatments On The Structure Of Humic Acids And Its Regulation On Nitrogen And Phosphorus

Humic acid could regulate the transformation and availability of nitrogen and phosphorus,while humic with different structures generates different regulatory effects.In this study,humic acid derived from weathered coal was processed with different methods（ultrasonic,H₂O₂,HNO₃,H₂O₂+HNO₃,sulfomethylation,H₂O₂+sulfonation,HNO₃+sulfonation,H₂O₂+HNO₃+sulfonation）to obtain the modified humic acids with different structure.Subsequently,the structure of humic acid and their corresponding regulation on nitrogen and phosphorus fertilizers were investigated to provide a theoretical basis for the development of high-efficiency humic acid materials.The main results were summarized as follows:（1）Nitric acid can significantly increase the nitrogen content of humic acid and enhance the stretching vibration of the carboxyl group C=O in humic acid.Sulfonation treatment can significantly increase the sulfur content of humic acid,enhance the stretching vibration of the C-O pair in humic acid,and introduce the sulfonic acid group into the humic acid structure.（2）When 6%hydrogen peroxide was used as the oxidant,the solution pH had a greater influence on the structure of humic acid than other reaction parameters（pH,temperature,liquid-solid ratio,time）.The change of temperature had a more significant effect on the structure of humic acid than liquid-solid ratio and time.（3）Humic acid can significantly retard the urea transformation.When humic acid was melted into urea with the addition ratio 2‰,5‰and 1%,humic acids treated with ultrasonic and oxidation showed a higher inhibition on urea transformation than the untreated humic acid.（4）Humic acid can reduced fixed rate of phosphorus.When added into phosphorus fertilizer with the ratio of 2%,humic acid with sulfonated treatments had a lower phosphorus fixated rate than the untreated one.（5）Compared with the common phosphate fertilizer,the phosphate fertilizer with sulfonated humic acid significantly increased the winter wheat yield and phosphorus use efficiency by an average of 14.1%and 12 percentage points,respectively.In 0-20 cm soil layer,the content of available phosphorus with sulfonated humic acid phosphate fertilizer treatment was higher than that with untreated humic acid by 17.4%.Among all treatments,sulfomathylated humic acid phosphate showed the best performance.