Phosphorus availability in savannah soils of western nigeria

Ayodele, O.J.

Tropical Agriculture 63(4): 297-338


ISSN/ISBN: 0041-3216
Accession: 006106639

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Total P was found to be low in 60 surface soils of western Nigeria savannah formed on igneous and metamorphic rocks; 41% was organic P. Average mobile P fractions were 4.1, 9.2, 19.6 and 10.0 mg kg-1 for saloid-bound, Al-, Fe- and Ca-P, respectively. All P forms except non-extractable P correlated significantly with organic matter and P uptake. Measures of active inorganic P were more related to P uptake than measures of organic P, and correlations indicated an order of P utilisation as saloid-bound P > Al-P > Ca-P > Fe-P. Six extractants were evaluated for assessing P availability; 0.05 N ADHDF (pH 7.0) which extracted least P had least correlation with P forms and P uptake. New Mehlich, Bray's P1 and 0.1 N AHDF extractants had high correlations with P uptake and inorganic P forms and are good indices of P availability in the soils. Lower correlations show that these extractants do not extract organic P and that mineralization of organic P, especially in soils with high organic matter content, affects P availability in tropical soils.