A simple model for predicting stand volume growth response to fertilizer application

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Abstract
The equation R = KTACZQ is used to predict cumulative stand volume growth response (R) to fertilizer application, where K is a constant and the last five (dimensionless) multipliers represent functions of time, amount of fertilizer applied, stand composition, stocking, and site quality, respectively. Site-specific input data requirements are stand composition expressed as percent responding species, stocking expressed as a percentage of normal stocking, and site index. The model was calibrated for Douglas-fir response to nitrogen by using data from Washington and Oregon. A preliminary test of the model and its calibration compares predicted responses to estimates of actual response derived from some fertilizer trials on Vancouver Island. Soil drainage class and foliar analysis data may help in qualitatively inferring whether the model's site quality function leads to overestimation of response. Future development of the model may include development and calibration of a predictively better site quality function which quantitatively uses site water regime and stand nutrient data.

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