Ayodele O.J, Omotoso S.O and Agboola A.A
Eight extractants: Bray’s P-1 (0.03N NH4F + 0.025N HCl), Bray’s P-1 + 0.01M EDTA, Bray’s P-1 + 0.005M DPTA, Bray’s P-1 + 0.01M EDTA, AHDF (0.1N NH4F.HF), AHDF + 0.005M DPTA, Modified Olsen’s 0.5M NaHCO3 + 0.01M EDTA, Modified Olsen’s 0.5M NaHCO3 + 0.005M DPTA and 1.0N NH4OAc (pH 7.0) were evaluated for predicting the availability of plant nutrients in thirty surface (0-15cm) soil samples collected from smallholder farmers’ plots in Ekiti State, Nigeria. The minus-one nutrient technique was used for maize grown in the greenhouse for 28 days and regression analyses carried out between amounts of nutrients determined with the extractants and uptake of respective nutrients. Correlation coefficients show that Bray’s P-1 and AHDF, with or without chelates, and modified 0.5MNaHCO3 can be used to assess available P and exchangeable K in the soils but not exchangeable Mg. The correlation coefficients of Bray’s P-1 + DPTA and 0.5MNaHCO3 + 0.01MEDTA with P, K, Mg, Cu, Zn and Mn uptake were significant and so meet one of the criteria for selecting them multipurpose extractants. The need to remove the dark colour from extracts would make the alkaline 0.5MNaHCO3 extractant less suitable for a rapid routine analytical procedure.
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