WEED EFFECTS ON EARLY K-NUTRITION AND P-NUTRITION AND GROWTH OF SLASHPINE ON A SPODOSOL

Slash pine (Pinus elliottii Engelm. var. elliottii) seedlings were gro wn on a Spodosol with and without total weed control. During the 187 d ays after planting, shoots and roots of both trees and weeds were samp led four times to determine (1) the effects of weeds on early K and P nutrition and growth of slash pine, (2) the correlation between either above-ground weed biomass or live coverage and the root-length densit y of weeds, and (3) provide a data set to test a nutrient uptake model . During the initial 187 days, trees in the weed treatment lost half t heir initial K content, yet biomass and P content remained unchanged. Concentrations of K in needles from this treatment concurrently decrea sed from 7.7 to 2.5 mg K g-1. Even trees in the weed-free treatment lo st K for the first 116 days before taking up significant amounts of K and P and increasing four-fold in biomass by Day 187. Tree root growth rates were also reduced in the presence of weeds. Grass root-length d ensity was poorly correlated with above-ground biomass or live coverag e (r2 values 0.37 and 0.47, respectively). Hence, above-ground attribu tes of weeds were considered poor surrogates for root-length density.