Micronutrient Limitations in Intensively Managed Southern Pine Stands.

Fertilization is a cost effective tool used for increasing growth and shortening rotation lengths in southern pine stands. To date, however, most attention has focused on N and P fertilization and relatively little is known regarding the supply and adequacy of micronutrients for southern pines. Here we report results from two minus micronutrient x nitrogen addition experiments in slash and loblolly pine in Florida. Both experiments were established on Spodosols and each utilized a split-plot design. The whole plot treatments consisted of four levels of nitrogen fertilization and the subplots included the minus-element micronutrient treatments. Each replication was separated into four nitrogen treatments (0, 100, 200, and 300 lbs/ac), and each nitrogen loading treatment was split into eight plots of approximately 20 trees each, consisting of various micronutrient fertilization treatments. The eight treatments were: All—a blend of all micronutrients; Nil—no micronutrient fertilization; and -B, -Cu, -Zn, -Fe, -Mn, and -Mo—a mix of all micronutrients except the element of interest (i.e., the -B plots are fertilized with copper, zinc, iron, manganese, and molybdenum). At the slash pine site, nitrogen increased tree height in the second and third year, but the effect of micronutrients was not significant in any year. At the loblolly pine site, tree heights increased between 0 and 100 lbs N/acre in the second and third year, and in those same years tree heights in the –Cu treatment were significantly less than the other treatments. The different response of loblolly and slash pine could be indicative of inherent species differences in nutrient demands, or could reflect a difference in soil nutrient levels that was detected in a soil profile analysis. The latter result indicated that Florida Spodosols can vary substantially in their micronutrient availability.