低分子量有机酸对土壤磷活化影响的研究

研究两种低分子量有机酸（柠檬酸和苹果酸）对土壤磷活化影响，并用修正的Hedley法测定土壤磷活化前后磷组分的变化。结果表明，低分子量有机酸能持续活化土壤磷，活化强度随低分子量有机酸浓度的增大而增强，并且柠檬酸活化土壤磷的能力强于苹果酸。低分子量有机酸能促进作物有效态无机磷组分（H2O-P和NaHCO3-Pi）的释放；同时还促进有机磷组分（NaHCO3-Po和NaOH-Po）的矿化。在低分子量有机酸浓度达到0.5 mmol/L以上时，其对土壤磷组分的活化量的顺序为:NaOH-Pi HCl-P NaHCO3-Pi H2O-P，即铁铝结合态磷 钙结合态磷 作物有效态磷。低分子量有机酸活化土壤磷的过程中伴有大量铁、铝释放，且铁或铝的释放量与磷活化量之间显著正相关（P0.05）。说明铁、铝结合态磷是低分子量有机酸活化土壤磷的主要磷源，并且其活化机制可能与铁、铝结合态磷的螯合溶解有关。

Effects of low-molecular-weight organic acids on soil phosphorus release

Effects of low-molecular-weight organic acids, citric acid and malic acid on soil phosphorus release were studied by a series of batch experiments, and the sequential phosphorus fractionation was analyzed in the soils before and after the extraction of citric acid or malic acid. The results show that the release rate of phosphorus from soil is increased with the increase additions of citric acid or malic acid, and that results in continuous release of phosphorus. Phosphorus release amount by citric acid is larger than that of malic acid. Low-molecular-weight organic acids can promote the release of the inorganic phosphorus fractions (H₂O-P and NaHCO₃-P_i), and mineralization of the organic phosphorus fractions (NaHCO₃-P_o and NaOH-P_o). When citric acid and malic acid are at high concentrations (≧0.5 mmol/L), the releases of phosphorus fractions is in the order of Fe-oxide- and Al-oxide- associated (NaOH-P_i) > Ca-associated (HCl-P) > plant-available inorganic P (NaHCO₃-P_i > H₂O-P). Large amounts of soluble iron and aluminum are also released with the additions of the low-molecular-weight organic acids, and the amounts are significantly correlated with the phosphorus releases (P<0.05). It suggests that Fe-oxide- and Al-oxide- associated inorganic P (NaOH-P_i) plays an important role in phosphorus release.