Comparison of Different Phosphorus Extractants in Soils of the Western State of Nigeria1
- Bernard F. D. Oko and
- Akinola A. Agboola2
Researchers in Western Nigeria have a problem in choosing a universally accepted extractant for soil test correlations. Many P extractants that are in use today have been adopted without sufficient investigation.
In the present study, 8 different P extractants were used in extracting P from 90 surface soil samples taken from 2 different ecological zones of the Western State of Nigeria. Soil P values for the different extractants before the first crop of rice (Oryxa saliva var. ‘OS6’ upland rice) were correlated with P uptake of the first crop, cumulative P uptake (P uptake for two croppings of 8 weeks each), and with cumulative yield (dry matter for two croppings). Soil P values after first crop were correlated with P uptake of the second crop.
Results suggested that different ecological zones may require different extractants, viz. Bray No. 2 (0.03 N NH4F + 0.1 N HC1) (r = 0.433*) for the swamp soils; Bray No. 4 (0.5 N NH4F + 0.1 N HC1) (r = 0.491**) for the Ikenne soils, and Bray No. 1 (0.03 N NH4F + 0.025 N HC1) (r = 0.383*) for the Ilora soils, but the general purpose extractant for rice in soils of the Western State was Bray No. 1 (r = 0.372***).
With the swamp soils, there was a negative correlation when soil P after first crop was correlated with second P uptake. The North Carolina extractant (0.05 N HC1 + 0.025 N H2SO4) (r = 0.462**) gave the best reliability for Ikenne soil. The Bray Nos. 1 and 2 were equally useful in both correlations for the above, as well as initial soil P with first P uptake although there was a slight preference in the former for the Bray No. 2 (r = 0.513**) over Bray No. 1 (r = 0.396*). For the 90 soil samples, Bray No. 2 (r = 0.279**) gave better correlation between soil P after first planting with second P uptake.
Correlation of initial soil P with one cropping of 8 weeks was better for swamp soils, whereas in Ikenne soils more confidence could be placed on correlations with second cropping and cumulative P uptake. For the Ilora soils and with a combined group (consisting of 90 soil samples) there was little or no significant difference in using either.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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