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STUDY ON THE PHOSPHATE RETENTION AND RELEASE IN SOME EAST PAKISTAN SOILS

D. H. KHAN and A. C. ROY
Plant and Soil
Vol. 21, No. 3 (December 1964), pp. 365-376
Published by: Springer
Stable URL: http://www.jstor.org/stable/42932080
Page Count: 12
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STUDY ON THE PHOSPHATE RETENTION AND RELEASE IN SOME EAST PAKISTAN SOILS
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Abstract

Four soils of different geo-morphological tracts of East Pakistan with prevalent subtropical humid climate were studied in relation to P-retention from native and added sources, and release of P induced by changes in soil chemical environment. A markedly high retention of P was observed in distinctly acidic Tejgaon clay and alkaline Ishurdi silty loam. Tejgaon clay has abundant ferruginous materials which would partly explain P-retention, and Ishurdi silty loam has appreciable CaCC₃ in the solum to account for marked P "unavailability". Moderate amount of P was retained in Tarabo silty loam and Rangpur silty loam which were lighter texture, near neutral in acid side, and contained inappreciable Fe₂O₃ and CaO. A considerable build up of P was observed in exchange positions on soil colloids from added P, irrespective of soil types. Considering the nature of adsorbed P-status and net increase in adsorbed P from added P, it was found that the calcareous Ishurdi silty loam had relatively lower value. Effect of Na-silicate and CaCO₃ on the release of phosphate, retained from added P, has been studied. A progressive release of phosphate with increase in concentration of Na-silicate up to 0.015 normality was observed in all the soils under study excepting Ishurdi silty loam. This has been taken to be due to the inactivation of Na-silicate in presence of free CaCO₃ in this soil. CaCO₃ treatment enhanced phosphate release in Tejgaon clay, whilst a negative effect was observed in Tarabo silty loam and Rangpur silty loam. Combined effect of CaCO₃ and Na-silicate showed some phosphate release, which was however less than that due to Na-silicate.

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