Weed effects on early K and P nutrition and growth of slash pine on a Spodosol

Abstract

Slash pine ( Pinus elliottii Engelm. var. elliottii) seedlings were grown on s Spodosol and without total weed control. During the 187 days after planting, shoots and roots of both trees and weeds were sampled 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 density 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 their initial K content, yet biomass and P content remained unchanged. Concentrations of K in needles from this treatment concurrently decreased from 7.7 to 2.5 mg K g −1. Even trees in the weed-free treatment lost 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 density was poorly correlated with above-ground biomass or live coverage ( r 2 values 0.37 and 0.47, respectively). Hence, above-ground attributes of weeds were considered poor surrogates for root-length density.