Phosphorus sorption capacity of low activity clay soils of South Western Nigeria and its usefulness in evaluating P requirement of rice
1996
Adetunji, M.T.
Field and laboratory experiments were conducted on 15 low activity clay soils in Ogun State of Nigeria to evaluate the relationships between P sorption capacity and some soil properties and the use of sorption indices in evaluating the P requirement of rice. Langmuir adsorption capacity (b) varied from 30.9 to 414.3 micrograms g-1. Although adsorption capacity was related significantly to a number of soil properties, citrate dithinonite bicarbonate (CDB) extractable Fe was the most important variable accounting for 99% of the variation in adsorption capacity. The solution P concentration (SPC) required to achieve 95% maximum grain yield of rice varied from 0.03 in a sandy clay soil to 0.19 micrograms ml-1 in a sandy soil, while the quantity of fertilizer P required to attain the solution P concentration (Standard Phosphate requirement, SPR) varied from 14.1 to 88.7 kg ha-1. Highly significant power function relationships were obtained between SPC and b (r = 0.93) and between SPR and b ( r = 0.93). The P buffering capacity (PBC) of the soils indicated that the soils are moderately buffered. However, SPR accounted best for the variation in grain yield of rice on the field (R2 = 0.90). The use of P sorption indices in estimating P needs of rice appears superior to the use of chemical extractants.
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