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Yampracha, S.; Attanandana, T.; Sidibe´-Diarra, A.; Srivihok, A.; Yost, R. S.

doi: 10.1097/
Technical Articles

The dissolution of rock phosphate (RP) in soils, a reaction fundamental to the effectiveness of direct application of RP, depends on both the RP and soil properties. Four RP materials of varying solubility, namely, Gafsa RP, Tilemsi RP, Taiba RP, and a local RP, Kanchanaburi RP, were incubated with six flooded acid sulfate soils to quantify factors affecting the dissolution of RP. The differences between dilute NaOH-P extracted from soils treated with and without RP materials (ΔNaOH-P) were used to estimate the dissolution of RP materials. A nonlinear Mitscherlich equation was used to describe the changes in ΔNaOH-P over incubation time. The coefficients of the fitted Mitscherlich equation were then regressed on soil and RP properties to develop an RP model. Soil acidity measured by pH and KCl-extractable aluminum (Al) were the soil properties that most affected RP dissolution and thus were included in the RP model. RP solubility as assessed using the second extraction with 2% citric acid as a percentage of rock and the particle size of RP (< 100 mesh) were the RP properties found most important in predicting dissolution and were include in the model. The calcium carbonate content of the RP affected the changes of pH in six acid sulfate soils after mixing with RP materials.

University of Hawaii, Honolulu, HI 96822. Dr. R. S. Yost is corresponding author. E-mail:

1Department of Agriculture. 2004. Soil and fertilizer management (in Thai). Available at (verified May 11, 2004).

Received July 27, 2005; accepted Oct. 10, 2005

© 2006 Lippincott Williams & Wilkins, Inc.