Study On The Effect Of Low-molecular-weight Organic Acids/Salt On Phosphorus Release Of Southern Forest Red Soil

Phosphorus is necessary for plant growth nutrients, is also a non-renewable mineral resources, P is still the most important agriculture and forestry production constraints of our country and the world, including limited phosphorus on red soil deficiency is particularly serious. Low of available phosphorous is one of the major limitations to Plant. Some studies suggest that low molecular weight organic acids played a significant role on phosphorus release. Therefore, this article is to start from the perspective of low molecular weight organic acids, Wuyi Mountain, Fujian, for example, research on the southern red soil of the mechanism of phosphorus release.Usually, inorganic phosphorus is 50 to 80% in total phosphorus, while the largest component of inorganic phosphorus is insoluble phosphate. We use citric acid and oxalic acid to do the activation of insoluble phosphorus in simulation found that the two acids with the same concentration under the action of the release of phosphorus in soil A is only about 60% in soil B, while the oxalic acid activation is about 83% of citric acid activation. Acid with different concentrations under the action of the two acids found that the concentration of 0.5 ~ 1mmol.l-1 is the cut-off point of phosphorus activation. Below this concentration the capacity of the weak activation of phosphorus, and more than this concentration, the capacity of activated phosphate start linear growth; Insoluble phosphorus found in the low molecular weight organic acids dissolved out, also with the increase of the concentration of low molecular weight organic acid/salt activation.Different types and concentrations of low molecular weight organic acids in different color time there is the strength of the color of phosphorus, ranging from inhibition. The results showed that the higher concentration of acid inhibition on the phosphorus color more serious. Concentrations of less than 0.5mmol/l they have no effect on phosphorus coloration, and when large enough (5mmol/l or above), they had strong impacts on phosphorous standard solutions coloration. And exceeding the concentrations above, prolonging P coloration time is ineffective. the two number concentrations, prolonging coloration time will reduce availability of coloration.Extraction test is the most important test of this issue is divided into several one-time extraction and continuous extraction. One-time extraction calculated by the formula: P(ug/g)=CV/m ,The sequential extraction was repeated with the formula: Pn=[Cn(Vn+ Vn-1′)-Cn-1 Vn-1′]/m。The results showed that: citric acid on phosphorus release better than oxalic acid, citric acid salt of the phosphorus release was better than oxalate. Under the action of two kinds of acid and its salts, phosphorus release were reached a maximum in 5mmol.l-1; The same concentration of citric acid, citric acid salt of P release as oxalic acid, oxalate of 2 times. Mainly due to citric acid is a triple, while oxalic acid is a dicarboxylic acid, the complexing ability of citric acid stronger than oxalic acid. In other experiments, the low molecular weight organic acids on the activation of red phosphorus is a slow and continuous dynamic process, the phosphorus will be continued activation. Sequential extraction for 10 times,with the increase in the number of extraction, although the activation of phosphorus release decreased, but still part of the continuous release of phosphorus, Release is also different sizes, you can see rules of phosphorous release along different temporal gradients.