Abstract: A pot experiment with black soil was conducted to study the effects of low molecular weight organic acids (LMWOAs) citric acid, oxalic acid, malic acid, and their mixture on the P accumulation in soybean ( Glycine max  L.) and the inorganic P form transformation in soil. LMWOAs promoted the P adsorption and accumulation in soybean plants, but the effect differed with growth stage. Applying LMWOAs decreased the contents of soil total inorganic P and unavailable P (Ca₁₀-P, Fe-P, Al-P, and O-P), but increased the contents of soil available P (Ca₂-P and Ca₈-P), suggesting that LMWOAs promoted the transformation of soil unavailable P to available P. The effect of test LMWOAs was in the order of citric acid > oxalic acid > mixed acid > malic acid. Moreover, the exudates from soybean roots also promoted the transformation of soil unavailable P to available P, resulting in the decrease of soil total inorganic P and its fractions except Ca₂-P. The contribution of soil inorganic P fractions to the P uptake by soybean was O-P > Fe-P > Ca₁₀-P> Al-P > Ca₈-P >Ca₂-P.

Key words: Oryza sativa, Allelopathic potential, Bioassay method, Application