MICRONUTRIENT DEFICIENCY IN SLASH PINE - RESPONSE AND PERSISTENCE OF ADDED MANGANESE

Micronutrient deficiencies are uncommon in slash pine (Pinus elliottii Engel. var. elliottii) and loblolly pine (Pinus taeda L.) stands. This study was conducted to determine the growth response of slash pine to individual micronutrient additions (Cu, Zn, Mn, Fe, B, and Mo) after uniform fertilization with N, P, and K at planting. The experiment was conducted on poorly drained Ultic Haplaquods in northeastern Florida using a randomized complete-block design with four replications. With the exception of Mn, micronutrient additions did not result in any significant volume growth responses. Beginning at age 7 yr and continuing through age 12 yr, the MnSO4-treated plots (26 kg Mn ha-1) averaged 2.2 m3 ha-1 yr-1 more stand growth than the control. Micronutrients (Mn, Zn, and Cu) were retained in the ecosystem at levels above background for the duration of the study. After 16 yr, approximately 14% of the added Mn was still present in the pine foliage, forest floor, and surface mineral soil. Results from this experiment, along with foliar-Mn data from 117 plantations on a wide range of lower Coastal Plain soils, suggest that Mn deficiency is unlikely to be widespread. Additional subacute micronutrient stress, however, will probably be found on poorly to moderately well-drained Spodosols, Ultisols, and Inceptisols when intensive silvicultural practices such as site preparation, macronutrient fertilization, and herbaceous weed control accelerate early stand growth.