Evaluation of phosphorus sorption capacity and phosphorus extractants for assessing phosphorus requirements of maize in western nigeria savanna soils
Ayodele, O.J.; Agboola, A.; Sobulo, R.A.
Communications in Soil Science and Plant Analysis 13(4): 295-308
ISSN/ISBN: 0010-3624 Accession: 005400456
Most of the P extractants developed for soils in temperate countries have not been able to successfully predict P requirements of crops in the tropics. Some workers have, however, suggested the use of sorption capacity at standard equilibrium P concentration to estimate fertilizer P requirements. P sorption capacity (psc), determined at 0.2 and 2.0 .mu.g/ml equilibrium P concentrations, were evaluated by greenhouse and field fertilizer experiments on savannah soils of western Nigeria. Correlation coefficients between psc at 0.2 and 2.0 .mu.g/ml P and yield attributes were very low and not statistically significant. The sorption values were also not able to predict P requirement in these soils because psc, and therefore, buffer capacity were low, difficult to measure accurately and did not approximate values required for maximum crop yields. Field P rates usually exceeded P requirements obtained from psc measurements. However, extractants which were able to indicate P status and availability in the soils correlated significantly with yield. It is suggested, therefore, that soil tests with suitable P extractants in addition to fixation studies which would evaluate P needed to increase soil P to a given level would have to be investigated for meaningful fertilizer recommendations.