变化的淹水条件对土壤磷素释放影响

Effect of of variable flooding conditions on soil phosphorus release

为了研究农业磷引起的水体富营养化机理,选择太湖流域宜兴稻麦轮作土,模拟了变化的淹水深度、水土比、不同酸度上覆淹水等,进行了淹水土壤磷释放研究。实验表明:土壤释磷量随淹水深度成比例增加,同一淹水深度土壤吸附/释放磷量出现周期性变化规律;实验得到一个临界水土比4:1,水土比小于4:1时,淹水中没有Fe2+溶出,且土壤磷释放缓慢,而水土比大于4:1时,磷释放强度增大,上覆淹水中开始出现Fe2+,且随水土比增大而增加;碱性淹水条件时土壤释磷量大于酸性淹水条件时的释磷量,其中上覆水pH9.78时土壤释磷量最大,而pH3.7时土壤总铁和Fe2+释放量最大,但此时释磷量很低,表明淹水中水—土体系Fe2+-Fe3+氧化物氢氧化物胶体一定程度上抑制土壤磷的释放。

Phosphorus released from flooded agricultural soils is a concern and it has been a leading cause of eutrophication of lakes and rivers. Phosphorus （P） released from agricultural soils in Taihu Lake watershed was simulated at variable flooding depths, water/soil ratios and pH values of flooding in flooded laboratory microcosms. The results show that P released from flooded soils increased with the increase of flooding depth, and the accumulative P content was highly correlated with flooding depth （R2=0.8451） . Moreover, P released-sported by soils was in periodic variation at the same flooding depth; The critical water/soil ratio 4：1 was obtained： less than 4：1 P release was lower and no Fe（ Ⅱ ） in flooding; more than 4：1 P release was greater and Fe（ Ⅱ） appeared, and it was in direct proportion to water/soil ratio. PH values of flooding significantly affected soil test Fe morphological transformation, and then controlled P release. P release was greater in alkali flooding condition than acid flooding condition, which was greatest in pH9.78 with the biggest content 3.4mg L-1. Ferrous iron and total iron release were greatest at pH3.70. While in this condition P content is lower. This indicates soil P release was greatly affected by Fe（ Ⅱ ）-Fe（Ⅲ）oxide-hydroxide colloidal matter in flooded soils.