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Kinetics of Phosphate Rock Dissolution in Acidic Soil Amended with Liming Materials and Cellulose

Dep. of Land Use and Applied Chemistry, Zhejiang Agric. Univ., Hangzhou, China

V. C. Baligar^* and K. D. Ritchey

USDA-ARS-ASWCRL, Beckley, WV 25802-0867

D. C. Martens

Dep. of Crops and Soil Environmental Sciences, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061-0404

W. D. Kemper

NPS-USDA-ARS, Beltsville, MD 20705-2350

*Corresponding author.

ABSTRACT

Phosphate rock (PR), coal combustion by-product (CCBP), lime-stone, and organic materials are promising amendments for low P, acid soils, and two or more of the amendments are commonly applied to improve crop yields in acid soil. However, the interactions between these amendments in acid soil are not fully understood. The effects of CCBP, limestone, and cellulose application on dissolution of North Carolina phosphate rock (NCPR) in an acid Lily loam (fine-loamy, siliceous, mesicTypic Hapludult) from West Virginia were examined in an incubation study. Based on the P-NaOH estimation method, 30% of the added NCPR was dissolved after 60 d of incubation. The NCPR dissolution decreased drastically with increasing rate of CCBP, particularly when it was applied together with limestone, whereas cellulose addition tended to enhance NCPR dissolution. Dissolution of NCPR was well described by first-order, Elovich, and Langmuir kinetic equations. The average r² values between the experimental data of NCPR dissolution and the three models were 0.829*, 0.851**, and 0.930**, respectively, for 17 soil samples with and without amendments. Half-life (t_1/2) from the first-order reaction could be employed as a simple measure of the NCPR dissolution rate. Constants A and b derived from the Elovich equation were related to the initial and average dissolution rate of NCPR. The potential maximum dissolution of PR from the Langmuir equation provided an estimate of the dissolution extent of NCPR. All four kinetic parameters, particularly t_1/2 and A, were closely correlated with CCBP application rates. These parameters appeared useful in evaluating the effects of CCBP application on NCPR dissolution in the acid soil and might also be applicable to predicting PR dissolution for a wide range of soils with different properties.

Received for publication December 1, 1994.