Interaction of initial seedling diameter, fertilization and weed control on Douglas-fir growth over the first four years after planting

Abstract

Planting larger stock, fertilization and added years of weed control are often employed to increase growth rate of plantations. We evaluated these techniques using a replicated factorial study design repeated in two diverse locations in western Washington State, USA. Two different sizes of planting stock, fertilizing at planting and in the following year, and two or three years of weed control were tested. No significant interactions among the treatment levels were found with all treatments influencing Douglas-fir growth in an additive manner. Fourth year stem volume gains were greatest from planting larger initial stock: planting seedlings 2 mm larger in basal diameter resulted in fourth-year stem volume gains of 35% and 43%. The fertilization treatments used produced early gains, but they were short lived. The third-year weed-control treatment had no observable effect on fourth-year stem volume or on volume growth in years three or four.