STUDIES ON ACTIVATION OF PHOSPHORUS BY ORGANIC MANURE IN SOILS AND ITS MECHANISMS──Ⅱ. Organic acids from decomposition of organic manure (matter)and their effect on activation to different artificial phosphate

In this paper, the mechanism of the activation of organic manure to differentform of phosphorus in the soils was studied by detecting the variety and quantity oforganic acids from decomposition of organic manures in the soils under differentconditions and their effect on dissolution to different artificial phosphate. The resultsshowed that the contents of all dectected organic acids could be increased significantlyby addition of pig feces, rice straw and cellulose to the soi1s under both aerobic andanaerobic conditions. The effect of seven kinds of detected organic acids on Pdissolution varied with the form of phosphate. Majority of the organic acids showed agood effect on dissolution of AI-P. Both oxalic and acetic acids were strong in dissolvingall Ca phosphates while citric acids showed an extremely strong ability in dissolving Fe-P. Citric acid should play the largest role in activation of phosphorus in the soils byorganic manure although its content was lower than others. The contribution of Fe-P inthe soils to the P activated by organic manure should be the largest in that of all formsof phosphates.