Mechanism of fulvic acid- and organic manure-mediated phosphorus mobilization in black soil at low temperature

Microcosm experiments were conducted to study the effects of fulvic acid (FA) and organic manure (OM) on soil phosphorus availability and acidic phosphatase activity in black soil at 10℃. The results showed that both FA and OM could enhance the availability of the soil P. Compared with the control, addition of FA and OM increased Olsen-P content by 54.5% and 111.5%, respectively. The phosphorus activation coefficients of FA and OM were 40.6% and 70.9%, respectively. During the period of incubation, soil organic phosphorus content reduced progressively in both FA and OM treatments. However, compared with the control (CK), soil organic phosphorus content in FA and OM treatments was increased by 20.8% and 42.3%, respectively. Moreover, treatment with both FA and OF was found to enhance acidic phosphatase activity, and soil organic carbon and dissolved organic carbon contents. Compared with CK, acidic phosphatase activity in FA and OM treatments was increased by 35.8%, 50.9%, and soil organic carbon content was increased by 42% and 35%, and dissolved organic carbon by 70.2% and 63.7%, respectively. The positive correlation was found either between acidic phosphatase activity and soil available phosphorus (r=0.925, p 0.01) or between DOC and soil available phosphorus (r=0.765, p 0.01) Fulvic acid- and organic manure-mediated phosphorus mobilization in the black soil tested may be attributed mainly to the enhancement of DOC content and acidic phosphatase activity caused by FA and OM.