Role of organic acids in phosphate mobilization from iron oxide

被引:173
作者
Johnson, SE [1 ]
Loeppert, RH [1 ]
机构
[1] Texas A&M Univ, Dept Soil & Crop Sci, College Stn, TX 77843 USA
关键词
D O I
10.2136/sssaj2005.0012
中图分类号
S15 [土壤学];
学科分类号
0903 ; 090301 ;
摘要
Phosphate deficiency often limits crop production in acid tropical soils because of the strong bonding of phosphate by Fe and Al oxides. Organic-acid exudation from roots is one reported plant adaptation to P deficiency. The objective of this study was to predict the efficacy of this P-deficiency stress response in different soil types by investigating the mechanism of organic-acid-induced P mobilization from different oxide minerals. Greater proportions of Fe and initially adsorbed P were released from ferribydrite when compared with goethite. More P was released and Fe dissolved at pH 4.0 than pH 5.5 or 7.0 from both oxides. For ferrihydrite, the order of effectiveness of the organic ligands for P release at pH 4 was citrate (19% of the total initially adsorbed P) > malate (14%) > tartrate (5%) >> oxalate = malonate = succinate (0.3-1.2%). For Fe release at pH 4, the order was oxalate (18% of total oxide suspension Fe dissolved) approximate to citrate (17%) > malonate (13%) > malate (8%) > tartrate (5%) >> succinate (0.02%). Faster phosphate readsorption in the case of oxalate than citrate probably accounted for the low apparent release of P by oxalate in spite of its greater Fe dissolution. At the smaller adsorbed-P concentration (1/4 of the adsorption maximum), the predominant mechanism of organic-acid induced P release was ligand-enhanced dissolution of the Fe oxide rather than ligand exchange. At 3/4 of the adsorption maximum., ligand exchange contributed to a greater extent to P release. Under low P-fertility conditions, organic-acid exudation would be more effective at increasing P availability in soils dominated by poorly crystalline than well-crystalline re oxides.
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页码:222 / 234
页数:13
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