Impact of weed control and fertilization on growth of four species of pine in the Virginia Piedmont

During 1999, a mixed stand of Virginia pine and hardwoods in the Piedmont of Virginia was clearcut and site prepared by burning. Three replications, containing strips of loblolly pine, shortleaf pine, Virginia pine, and Eastern white pine, were planted at a 3 m x 1.5 m spacing during February to June, 2000. The strips were subsequently split to accommodate four different silvicultural treatments: (1) check - no treatment; (2) weed control; (3) fertilization; and (4) weed control plus fertilization. Herbicides were applied in 2000 (broadcast Oust®), 2001 (directed spray of Garlon® plus Roundup®), and 2003 (directed spray of Roundup®) to control both herbaceous and woody competition. Fertilizers containing N, P, and K were applied in 2001, N only in 2002. Crop tree survival was highest for loblolly pine, followed by Virginia pine, shortleaf pine and, lastly, Eastern white pine. There was a significant species x silvicultural treatment interaction at this site. Total height after 4 years followed the pattern loblolly pine>Virginia pine=shortleaf pine>white pine. In loblolly pine, weed control and fertilization increased growth compared to the check. In white pine, there was no significant difference between weed control and weed control plus fertilization compared to the check. However, hite pines in the fertilized only plots were shortest due to increased hardwood competition that overtopped the pines.