Importance of weed control, fertilization, irrigation, and genetics in slash and loblolly pine early growth on poorly drained spodosols

Abstract

Research reported here has evaluated interactions of factors limiting the biological potential of slash pine ( Pinus elliottii var. elliottii Engelm.) and loblolly pine ( P. Taeda L.). Water and nutrients were manipulated by irrigation, weed control, and intensive fertilization. Genetic factors were incorporated as (1) improved loblolly seedlings from a commercial clonal seed orchard and (2) slash seedlings from four fast-growing, open-pollinated seed-orchard clones. Three replications of a 2 × 2 × 2 factorial experiment were established on a Typic Haplaquod soil in northern Florida using four cultural treatments: no treatment (F0H0); weed control (F0H1); fertilizer (F1F0); and combination of weed control and fertilizer (F1H1) for each species. During the first year there were large, sustained responses to all cultural practices. Loblolly and slash pine showed similar growth responses and had a lengthened growing season (60–100 days). Slash pine growth was superior to that of loblolly. Growth responses observed during the first year continued. After 4 years, irrigation had no measurable effect on tree growth. Both pine species responded equally to F1H0 and F0H1, but slash retained a slight edge. Extra nutrients]available via fertilizer, reduced competition, or additional rooting space, increased slash-pine volume index from an average of 2.0 m 3 ha −1 (F0H0) to 11.90 and 13.59 m 3 ha −1 (F0H1 and F1H0, respectively). The F1H1 treatment produced the largest slash-pine response, diameter at breast height ( D bh) averaged 9.84 cm, height reached 5.02 m, and volume index rose to about 22.94 m 3 ha −1. With teh F1H1 treatment, average loblolly-pine height and volume exceeded that of the average slash pine. At age 4, the growth response due to increased nutrient supply was 13–29 times that of the best genetic response within F0H0 trees of the four slash-pine progenies. The best-growing slash-pine family (6–56) exceeded loblolly-pine growth under all four treatments and approximated the vigor shown by slash pine in the southern hemisphere.