Comparison of 6 extractants for determining available phosphorus in soils from tonga

Mcgaveston, D.A.; Widdowson, J.P.

Tropical Agriculture 55(2): 141-148


ISSN/ISBN: 0041-3216
Accession: 005004534

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Six different extractants were evaluated ad indices of the available P of topsoil and subsoil samples of 9 Tongan soils. Regression and correlation analysis between percentage yield of green panic (Panicum maximum var. Trichoglume) and P extracted by various methods showed that the Bondorff extracts (0.1 M H2SO4) and 0.5 M H2SO4 provided good indices of available P. For all Tongan soils the P extracted by the Bondorff method gave the best correlation with percentage yield (Y = 2.19 (Bondorff P) -0.37 where Y = percentage yield of dry matter and P = mg P extracted from 100 g of soil, r = 0.80). For soils derived from andesitic ash both extractants gave good correlations with plant yield (Y = 2.25 (Bondorff P) -1.22, r = 0.81 and Y = 0.61 (0.5 M H2SO4 P) -3.80, r = 0.83). The Bondorff reagent and 0.5 M H2SO4 extract different proportions of plant available P from the Fe phosphate fraction of the andesitic soils and 0.5 M H2SO4 also extracts P from Ca phosphates in soils derived from coralline sand.