柠檬酸对红壤磷的持续活化效应及其活化机理的探讨

采用不同浓度的柠檬酸对红壤进行磷的持续活化试验。结果表明：随着浸提次数的增加，磷的活化量逐渐降低，但仍有少量的磷释放出来，且活化强度随着柠檬酸浓度的增大而加强。浸提前后土壤样品的无机磷分级结果表明：被柠檬酸活化的磷主要来源于土壤中Al-P、Fe-P及Ca—P中的磷，也有部分来自于有机形态的磷，同时柠檬酸能够促进土壤中闭蓄态磷（Oc—P）的形成与积累。Al-P、Fe-P及Oc—P中磷的活化量，受柠檬酸浓度的影响较大。柠檬酸浓度在5mmolL^-1和10mmolL^-1时，其被活化的量大小依次为Ca—P〉Al-P〉Fe-P；而柠檬酸浓度在100mmolL^-1时，其被活化的量为Fe—P〉Al-P〉Ca—P。

PERSISTENT ACTIVATING EFFECT OF CITRIC ACID ON PHOSPHORUS IN RED SOIL AND ITS MECHANISM

An experiment was carried out of persistent activating effect of citric acid on phosphorus in red soil.Results show that amount of the phosphorus activated decreased gradually with the increase in frequency of extraction,but never down to nil,and the activation intensified with the increasing citric acid concentration.Fractionations of inorganic phosphorus in the soil samples before and after the extraction show that phosphorus was activated by citric acid mostly from the fractions of Al-P,Fe-P and Ca-P,and some from the fraction of organic phosphorus,and that citric acid accelerated formation and accumulation of Oc-P in red soil.Effect of concentration of citric acid on activattion of phosphorus from Al-P,Fe-P and Ca-P was very clear.When the concentration of citric acid was 5 mmol L-1 and 10 mmol L-1,the fractions were in the order of Ca-P>Al-P>Fe-P in terms of amount of phosphorus activated,but when it was 100 mmol L-1,the order was:Fe-P>Al-P>Ca-P.