Soil testing for phosphorus availability to some conifers in British Columbia

Michael Patrick Curran
Two complementary investigations were conducted as a preliminary study to find an adequate method for estimating "available" phosphorus (P) in British Columbia forest soils. Eight soil materials provided a range of British Columbia forest soil properties, P forms and P levels. The 12 methods evaluated were H₂O-soluble P, Truog, modified Olsen (using polyacrylamide to remove coloured organic constituents), Bray P₁ and P₂, modified Bray P₁ and P₂ (longer extraction time), modified double-acid
more » ... ied double-acid (0.05 N HCl + 0.025 N H₂SO₄, using polyacrylamide), NH₄OA[sub c] (ammonium acetate) at pH 4.8, modified (using polyacrylamide) NH₄HCO₃-DTPA (diethylene triamine pentaacetic acid), 0.01 _N HC1, and new-Mehlich. The first study investigated relationships among 12 soil test methods for estimating soil available P and 4 chemical P fractions. The 4 chemical P fractions were obtained by a modified Chang and Jackson procedure. The second study evaluated the test methods as indices of "tree-available P" through a greenhouse pot trial with the 8 soil materials x 2 P treatment levels (P added and control) x 3 tree species (Douglas-fir, western hemlock, and lodgepole pine). The first study revealed that most methods extract the greatest amount of P from forest floor samples (apart from a P fertilized soil) and the least from Podzolic B horizon samples. Similar to the literature, P levels obtained by a number of the methods are significantly correlated with each other. Modified Olsen values are significantly correlated with values from the greatest number of other methods. The 4 Bray methods, modified double-acid and new-Mehlich methods yielded the next largest group of significant correlations. Water-soluble P and 0.01 HCl values were seldom significantly correlated, and NH₄OA[sub c] (pH 4.8) values were not correlated, with other method test values. Contrary to agricultural soils literature, only one significant correlation existed between the soil test values and P forms: NH₄OA[sub c] (pH 4.8) extraction with the Ca-P fraction. Corr [...]
doi:10.14288/1.0095986 fatcat:j6vfsmhrx5chpn552fzby7m5h4