LONG-TERM EFFECTS OF FOREST FERTILIZATION ON SITE ORGANIC-MATTER AND NUTRIENTS

The long-term effects of time-of-planting fertilization on the accumulation and distribution of above- and belowground organic matter and nutrients are largely unknown for intensively managed southern pine (Pinus spp.) stands in the U.S. lower Coastal Plain. These effects were investigated using a 25-yr-old slash pine (P. elliottii Engelm. var. elliottii) plantation in north Florida. The experiment was conducted on a poorly drained, P-deficient Rutlege soil (sandy, siliceous, thermic Typic Humaquept) using a randomized complete block design. The experimental treatments included: (i) control, (ii) NPK (112, 39, and 45 kg ha-1 using ordinary superphosphate [OSP] + N and K) and (iii) P (314 kg P ha-1 using ground rock phosphate [GRP]). Fertilization significantly increased total aboveground organic matter accumulation, with levels for the OSP+NK and GRP treatments being 2.5 and 1.8 times greater than the control, respectively. Levels of soil organic matter measured to a depth of 91 cm did not vary, however. Treatment effects were found for P, K, and Ca levels in the fertilized slash pine biomass components and surface soil. Long-term differences in extractable soil P were most pronounced for the GRP treatment, with concentrations in the surface 15 cm being 2.6 times greater than the control; only the high P treatment sustained foliar P levels within the published critical range for slash pine. While field trials are required to confirm actual fertilizer carryover effects, results from this experiment suggest that sites previously fertilized with operational P rates (40410 kg ha-1) will again require treatment when establishing the next pine rotation.