Organic Acid Promoted Dissolution of Phosphate in Mineral Mixtures: Implications for Phosphorus Bioavailability and Soil Fertility.

Secretion of low molecular weight organic acids by plants and

microbes in response to phosphorus deficiency has been hypothesized to

be a primary biochemical process for nutrient (Fe, P) bioavailability

and amelioration of Al toxicity in soils; yet, critical gaps in

molecular scale characterization of this primary biochemical process

remain. In particular, the effect of sorption of organic acids and the

role of phosphate solid state speciation on dissolution efficacy of

organic acids is not well understood. We formulated binary and ternary

mineral-mixtures pertinent to mineral-P sorbents in acid and alkaline

soils and characterized phosphate sorption and organic acid P

dissolution at pH's relevant to soils. An integrated P K-XANES and

EXAFS and transmission electron microscopy approach was used. Lab

scale studies suggest that regardless of organic acid sorption on

mineral-phases, organic acids are effective in releasing P at acid and

alkaline pH's; this mechanism should be harnessed for improving soil

fertility rather than addition of inorganic P fertilizers that can

degrade soil quality. citric acid is most effective in releasing P

from mineral sorbents.