Abstract: 【Objective】The difference between HA (raw humic acid) and PHA (humic acid which extracted from humic acid enhanced phosphate fertilizers (HAP)) on fertilizer-phosphorus migration, Ca²⁺ and phosphate adsorption characteristics was systematacially compared to provide the theoretical basis for the study on high-efficiency mechanism of humic acid enhanced phosphate fertilizer.【Method】In this study, HA, HAP, and conventional phosphate fertilizer were prepared in the laboratory, and PHA was extracted by adjusting the pH of HAP’s solution based on the method of alkali-extraction acid-precipitation. Effects of HA and PHA applicated with phosphate fertilizer on the migration of fertilizer-phosphorus in soil was investigated. The addition of HA or PHA accounted for 0.5% and 5% of the application amount of phosphate fertilizer, and marked with 0.5HA+P, 0.5PHA+P, 5HA+P, and 5PHA+P, respectively. Only phosphate fertilizer application (P) and no fertilizer application (CK) were arranged at the same time. In addition, the adsorption characteristics of HA or PHA on Ca²⁺ and phosphate were studied to reveal the mechanism that HA and PHA showed different performance on phosphorus migration. 【Result】Both HA and PHA could promote the migration of fertilizer-phosphorus. Phosphorus could migrate to 42 mm vertical distance from the fertilizer layer under the treatment of P, while it could reach 46 mm and 50 mm away from the fertilizer layer, respectively, when phosphate fertilizers application combined with HA and PHA. This result resulted from the fact that HA or PHA had a higher adsorption capacity on soil Ca²⁺, and the application of HA or PHA reduced phosphorus fixation. The cumulative percentage of soil available P in total P application tended to be stable after 42 mm away from the fertilizer layer, and 0.5 HA+P ≈ 5PHA+P > 5HA+P > 0.5PHA + P > P. The promotion effect of PHA on fertilizer-phosphorus migration would be enhanced with the addition of PHA increase, while HA was the opposite. Which might be related to the stronger mobility and the weaker phosphate adsorption of PHA than that of HA. The adsorption of Ca²⁺ by HA and PHA was the result of membrane diffusion and intra-particle diffusion. However, the difficulty of Ca²⁺ diffusion to the surface of PHA particles was lower than that of HA, and the difficulty of Ca²⁺ diffusion in the interior of PHA particles was higher than that of HA. Langmuir isothermal adsorption model could well fit the isothermal adsorption curves of HA or PHA on Ca²⁺, and the theoretical maximum adsorption capacity of HA on Ca²⁺ was higher than that of PHA, but the adsorption of PHA on Ca²⁺ was mainly chemical adsorption.【Conclusion】Both raw humic acid (HA) and humic acid extracted from humic acid enhanced phosphate fertilizers (PHA) have certain ability to adsorb Ca²⁺, so they can promote the migration of fertilizer-phosphorus in the soil. However, the migration distance of fertilizer-phosphorus of PHA was longer than that of HA, when phosphate application was combined with HA or PHA. This may be one reason why PHA can improve the use efficiency of phosphate fertilizer.

Key words: humic acid enhanced phosphate fertilizer, humic acid, fertilizer-phosphorus migration, calcium ion, adsorption