EVALUATION OF METHODS OF EXTRACTING SOIL CATIONS FOR FOREST PRODUCTIVITY STUDIES IN SOUTHWESTERN BRITISH COLUMBIA

Abstract

The NH₄OAc pH 7 method has been used traditionally to assess the availability of cations in soils for tree growth in coastal British Columbia but there have been no attempts to assess the validity of the method for this purpose. This objective was accomplished by determining the quantities of extractable cations (K, Mg, and Ca) in 42 forest soils in the Coastal Western Hemlock Biogeoclimatic Zone of British Columbia using four different extraction methods. The methods used were the NH₄OAc pH 7, NH₄OAc pH 4.8, 10% HCl, and 1% citric acid methods. A stepwise elimination multiple-regression technique was used to test the relationship of extracted cations to forest productivity. The amounts of cations extracted by the NH₄OAc method were well-correlated with those extracted by each of the other three methods. Of the cation quantities extracted, those of Ca were best, although still poorly correlated with productivity. Of the extraction methods, the NaOAc method yielded quantities most closely correlated with productivity and is recommended for use in assessing the cation status of forest soils in the Coastal Western Hemlock biogeoclimatic zone.