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Experiments on the effects of phosphate applied to a Buganda soil: III. A chemical study of the soil phosphate, the fate of fertilizer phosphate and the relationship with iron and aluminium

Published online by Cambridge University Press:  27 March 2009

P. H. Le Mare
P. H. Le Mare
Affiliation:
Cotton Research Corporation, Cotton Research Station, Namulonge, Uganda*
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Summary

Solubility products (pKsp) for iron and aluminium hydroxides and phosphates have been determined in a Buganda acid clay loam. Significantly greater values, i.e. lower solubility products occurred when determined at a soil:solution ratio of 0·4 than at 0–8. In the most acid soils, pH 4·8–5·0, values of pKsp) were consistent with the possibility that iron and aluminium concentrations were controlled by goethite and gibbsite. Above pH 5 the data indicated that these minerals were not effective. The maximum pKsp) value for iron phosphate was too small to be consistent with that for strengite, indicating that this mineral did not affect phosphate concentration in the soil; the maximum value for aluminium phosphate was consistent with that for variscite but the occurrence of this mineral cannot be deduced from the data. Triple superphosphate applied at 8 cwt per acre or less was converted within 2 years to a very insoluble form, having a solubility similar to that of variscite; with 16 cwt per acre the phosphate concentration was much greater than with the smaller dressings after this period and the soils appeared supersaturated with variscite.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 70 , Issue 3 , June 1968 , pp. 281 - 285
Copyright
Copyright © Cambridge University Press 1968

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References

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