The Effects And Mechanisms Of Of Organic Acids On Phosphorus Release Under Soil Column Leaching Conditions

As the continuously development of root micro ecological system, the ecological function of organicacid has been gradually concerns. To simulate plant roots secreting organic acid, and to investigate theactivation and mechanism of organic acid on phosphorus release in plant rhizosphere is still an importantresearch subject of plant nutrition and soil chemistry field. Although some related researches have alreadycarried out both at home and abroad, and made some progress, most of the results were came from themethods of batch experiments. The effect of organic acid on the activation process of P release,characteristics and vertical migration and transformation of soil P under the continuous leaching conditionsis still limited, and so that there is more space for discussing and developing.In this article, adopted the method of continuous leaching of soil column leaching, studied the effect ofseveral low molecular weight organic acid on constantly release characteristics of soil P in differentconditions, and the variation characteristics of organic acid, the solution pH value and Ca, Mg, Fe, Al in theleachates, analyzed the vertical distribution and the variation of different P fractions after the soft leaching,disscussed the mobilization of five different synthetic phosphate compounds by organic acids and itsactivation pathway. The main research conclusions of this article was shown as follows:1. In the continuous leaching condition, the continuous activation ability of different kinds of organicacid on soil P in the single saturated cationic state is different. In the condition of same concentration, theaccumulated activation ability of citric acid on soil P is the most powerful; the activation ability of oxalicacid can be quite with citric acid in high concentration, while it is will below citric acid and acetic acid inthe middle and low concentration; continuous activation ability of acetic acid on soil P is stronger.2. In the continuous leaching condition, the effect of organic acid concentration on continuousactivation ability of organic acid on soil P is not same. No matter high concentration or low concentration,citric acid always show a strong activation ability on soil P, activation ability of oxalic acid be quite withcitric acid only in high concentrations, while activation ability of acetic acid is relatively low in anyconcentration conditions. Elovich, weight function equation and parabolic diffusion equation can fittingrelease process of soil P very well. in the organic acid leaching conditions, the size order of the initialinstantaneous release rate of soil P leaching with each organic acid is: citric acid> oxalic acid> acetic acid,and the activation rate of organic acid on soil P decrease with the extension of time; all the three organicacids can increase the relative diffusion coefficient R of soil phosphorus and all of them promote thediffusion behavior of soil P.3. In continuous leaching process, acidity provide by organic acid （measured on hydrogen ion）, timeof organic acid reacted in soil （measure on leaching speed）, and microbial activity can influence continuousactivation ability of organic acid on soil at some degree. In the condition of low concentration organic acidcontinued leaching, acidity a provide by citric acid and acetic acid can promote the release of P, thepromoting function of acidity mainly embodied in the leaching middle and late, role of acidity provide bylow concentration oxalic acid is not significant due to the influence of calcium oxalate; In high velocitycontinued leaching condition, activation quantity of soil P made by citric acid and acetic acid increase, while oxalic acid treatment has not significant change; microbial slow the continuous activation function ofthree organic acid on soil p at certain degree, and its inhibitory on citric acid is most obvious.4. In continuous leaching function conditions, the concentration of organic acid forms in drench liquidare changing, but eventually be stable. In leaching process, the proportion of solution state organic acid indrench liquid account total organic acid increases accordingly, the proportion of decomposition state reduce,the proportion of sorption state organic acids change irregular. In the whole leaching process, theproportion of dissolve state organic acid is biggest, but between it with accumulation release quantity ofsoil phosphorus no significant correlation, while sorption state and decomposition state organic acid withaccumulation release quantity of soil p is significant and very significant correlation respectively.5. In continuous leaching process, Ca, Mg, Fe, Al in soil are constantly released with the activation ofsoil P. The higher concentration of organic acid, the more of Ca, Mg, Fe, Al ion pour out. The releaseability promote by citric acid with its activation ability on soil P have very good consistency. Releaseability on Fe, Al of Oxalic acid better than citric acid in general.6. Organic acid continued leaching can promote phosphorus to move down in soil, and highconcentration organic acid can accelerate the transfer of soil phosphorus. In the form of phosphorus, highconcentration organic acid leaching can significantly reduce the content of NaOH-Pi and HCl-P, and thisshow that high concentration organic acids is beneficial to the release of Fe, Al combination state phosphateand calcium bound phosphorus, but even if high concentration organic acid is also still hard to activate theResidual-P, influence of organic acid continued leaching on soil organic P is no specific order.7. In Five kinds of synthetic phosphate, Ca₂-P and Ca₈-P is most easily activated, followed by Al-P,Fe-P, and Ca₁₀-P is the most difficult activated. Activation function of low molecular weight organic acidon synthesis phosphate affect by the concentration of organic acid, in high concentration processingconditions, the sequence of activation ability of the five types of synthesis phosphate is oxalic acid≥citricacid> acetic acid; under the middle concentration condition, the sequence is citric acid≥oxalate quartile>acetic acid, but low concentration organic acid is hard to activate the synthetic phosphorus source. Agingfunction can reduce the effectiveness of the synthesis phosphate to certain extent, the effect of agingfunction on activation function of oxalic acid on synthesis of phosphorus source is smaller than effect oncitric acid and acetic acid.8. The activation mechanism of citric acid on Ca₂-P, Ca₈-P and Al-P in synthesis phosphate is thecommon function of protons and organic anion, the release of phosphorus in iron phosphate mainly comesfrom the activation organic acid radical, and the activation of Ca₁₀-P is almost entirely depends on protonrole. High molecular weight humic acid can also promote the release phosphorus in the five kind syntheticphosphates, and all the three calcium bound phosphate can be well activited by humic acid.