Composite design versus factorial experiments in forest fertilization trials

The applicability of the rotatable second-order central composite design in forest fertilization studies was tested. The results indicated that the quadratic response equation specified by the central composite design was inadequate in approximating the response surface of white spruce (Piceaglauca (Moench) Voss) seedlings to fertilization with N, P, and K. Conventional factorial experiments arc useful not only in testing hypotheses of various effects but also in deriving an equation that adequately approximates the true response surface. Using the derived regression equation, seedling growth response to various rates of fertilizer application can be predicted and an optimal fertilizer regime can be determined.