RELATIONSHIPS BETWEEN GROWING-SEASON SOIL WATER-DEFICIT, MINERALIZABLE SOIL-NITROGEN AND SITE INDEX OF COASTAL DOUGLAS-FIR

Relationships between measures of soil water availability, available soil macronutrients and site index of coastal Douglas fir were examined in 53 stands. Growing-season water-deficit was able to explain the most variation in site index of all soil water-balance measures examined (R2 = 0.42). Of all soil chemical properties examined, mineralizable N in the surface 30 cm of the mineral soil and in the forest floor accounted for the most variation in site index (R2 = 0.54). Multiple regression of the natural log of mineralizable N, and growing-season water-deficit on site index gave an R2 of 0.63. Use of mineralizable N as a measure of N availability is supported, and interactions between water-use efficiency and stand N status are suggested. © 1990.