Effects of Exogenous Humic Acids on Forms of Organic Phosphorus in Three Contrasting Types of Soil

Abstract

A laboratory incubation study was conducted to examine the effects of exogenous humic acids on the forms of organic phosphorus (P) in three contrasting soil types: red soil, brown soil, and drab soil. Results indicated that the Olsen P concentration increased in all the three types of soil with addition of the humic acid extracts, with the magnitude of increment ranked in a sequence of brown soil > drab soil > red soil. For the soil organic P fractions, addition of the humic acid extracts increased the labile organic P and moderately labile organic P concentrations while reducing the moderately resistant organic P and highly resistant organic P concentrations, suggesting that the exogenous humic acids could enhance transformation of organic P from resistant forms to labile forms. The activation of organic P by addition of the humic acid extracts varied with soil type, and this variation was related to soil characteristics.

Keywords:

• Availability
• humic acids
• organic phosphorus fraction
• soil organic matter

Acknowledgment

This research was supported by the National Basic Research Program of China (2012CB416906) and the National Natural Science Foundation of China (31100466). We thank Jing He for assistance with the laboratory analyses. Constructive comments from Osbert J. Sun have helped greatly improve the article and are greatly appreciated.