FORAGE RESPONSE TO N-FERTILIZATION, P-FERTILIZATION, AND S-FERTILIZATION ON CLEAR-CUT LODGEPOLE PINE SITES

The response of selected plant species to a single application of fact orial combinations of nitrogen (N), phosphorus (P), and sulfur (S) on 2 lodgepole pine (Pinus contorta Dougl.) clearcut-logged sites in Brit ish Columbia was evaluated over 3 years. Increasing N rates typically resulted in higher forage standing crop on both sites, in all years, b ut standing crop at Fly Creek was nearly double that at Beaverdam Lake . On both sites, forage yields peaked at 400 kg N/ha in 1982 and carry -over of the fertilizer effect lasted for 3 years although yields decl ined annually. Addition of P to N applications enhanced (P<0.05) total standing crop, other grass standing crop, and pinegrass (Calamagrosti s rubescens Buckl.) standing crop at Beaverdam Lake and grass standing crop at Fly Creek, but had no effect (P>0.05) on other species and gr oups. Sulfur, added to N applications, enhanced total yields compared to control on both clearcuts although at Fly Creek this response nearl y doubled that produced at Beaverdam Lake. Nitrogen fertilization incr eased (P<0.05) pinegrass crude protein (CP) content, particularly in t he first year after fertilization. Acid detergent fiber (ADF) generall y increased in response to increasing N levels in 1982, but declined c ompared to control in 1983 and 1984. Elevated forage CP levels, litter N concentrations, and soil N levels in 1984 indicated that the carry- over response on these forest sites resulted directly from N remaining in the soil or again becoming available for plant growth.