Evaluating Soil Nutrient Regime for Black Spruce in the Ontario Claybelt by Fertilization

Fertilization screening trials testing a standard NPK application were conducted in 29 mature black spruce stands growing on diverse Claybelt sites. The objective was to evaluate several methods of predicting soil nutrient regime, and validate a nutrient-related ordination axis of the regional Forest Ecosystem Classification (FEC) system. Diagnosis by vector analysis of current needle responses in dry weight and macronutrient concentration and content suggested that of all nutrients added N was most limiting for black spruce growth. Potential fertilizer response was measured by the change in unit needle N uptake (content) occurring in the first season after treatment. Significant increases (as high as 63% over the control) were detected in about half the trials suggesting that the stands were established on sites varying in soil fertility. Foliar N response was subsequently correlated against more rapid predictors of site productivity such as stand growth parameters site index, stem analysis, and chemical analysis of unfertilized soil and foliage. Of these only measures of fall-sampled, current needle N content correlated adequately (r = −0.72) with potential fertilizer response. This response factor was also significantly correlated (r = 0.71) with the coordinate values of the FEC-ordination diagram indicative of site nutrient regime, supporting evidence that the axis reflects a continuum of soil N availability. Key words: Nitrogen, foliar analysis, response prediction, site evaluation, forest fertilization, Picea mariana