Abstract:Low of available phosphorous is one of the major limitations to crop production. Mobilization of insoluble phosphates by root exudates plays an important role in improving P nutrition of crops. Three types of soils collected from Hubei province were tested to analyze the changes of inorganic phosphorus fractions and available phosphorous after incubated with addition of various organic acids and different phosphorus sources. The results indicated that P added as fertilizer increased available phosphorous in all soils. On soils of pH4.6 and pH6.8 the fertilized phosphorus was transformed into Fe-P and Al-P mainly. However, on soil of pH8.3 the fertilized phosphorus significant increased content of Ca-P. Organic acids had significant influence on available phosphorous except malic acid. Application of organic acids decreased the content of Al-P and increased the content of Ca-P in neutral soil, in the order of Oxalic acid > Citric acid > Malic acid. Phosphorus was activated by organic acid mostly from the fractions of Al-P and Fe-P in acid soil and neutral soil, but fractions of Ca-P in alkali soil, at the same time, organic acid accelerated formation and accumulation of O-P in the three soils.