Dissolution of North Carolina Phosphate Rock in Acid Colombian Soils as Related to Soil Properties

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Abstract
Information on the dissolution of phosphate rock in soils as related to soil properties is needed in order to understand the solubility behavior of the phosphate rock in soils as related to crop response. This study was conducted to determine the relationships between the dissolution rate of North Carolina phosphate rock and selected chemical properties of 16 acid Colombian soils. A modified Elovich equation, Ct =Co − (1/β) ln (αβ) − (1/β) ln t, was used to describe the dissolution of phosphate rock in the soils. In the equation, Ct is the P concentration in water extract at time t, Co is the maximum P concentration in the water extract when t→0, α and β are constants. Of the various soil properties studied, the best correlations of reactive Al were a simple linear relationship with β and a log‐log relationship with α. Results from tests with two other acid soils from Colombia showed these relationships allow prediction of the dissolution rate of the phosphate rock in other soils from a single measurement of reactive Al content.Phosphorus sorption capacities of the 16 soils were correlated with amounts of reactive Al or active Al but not with amounts of free Fe2O3 and exchangeable Al in the soils. Amounts of water‐extractable P in the soils treated with concentrated superphosphate (CSP) or the phosphate rock decreased as P sorption capacity increased; however, the relative amounts of water‐extractable P of the phosphate rock with respect to CSP increased as P sorption capacity increased. This suggests that the relative agronomic effectiveness of phosphate rock compared with CSP would be highest on the strongly P‐fixing soils.

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