Growth response of longleaf pine (Pinus palustris Mill.) seedlings to fertilization and herbaceous weed control in an old field in southern USA

摘要

The resurgence of longleaf pine (Pinus palustris Mill.) planting in the past decade has fueled the need for better understanding of the adaptation of current silvicultural practices to pine species better. Use of herbicides and fertilizer to accelerate the emergence of longleaf pine seedlings out-of-the-grass stage has rapidly started to replace prescribed fire as the preferred management practice in plantations. The objective of this study was to measure the effects and interaction of weed control and fertilization on longleaf seedling growth and survival. A 2 x 2 factorial study, installed as a randomized complete block design was conducted over two growing seasons in Santa Rosa County, FL. Hexazinone (0.74 kg ad. ha(-1)) and Sulfometuron methyl (0.16 kg a.i. ha(-1)) were applied on an annual basis, while fertilizer (10-10-10) was applied at the rate of 560 kg ha(-1), 5 months after planting. Except for survival, the effects of fertilizer and weed control were not additive by the end of the second growing season. Longleaf pine survival was highest for the weed control (84%) and lowest for the fertilizer (53%) treatments. This pattern was repeated for root collar diameter (RCD) and height growth. Seedling height for weed control and control treatments were 33.4 and 13.4 cm, respectively, at the end of the second growing season. Regression analysis revealed that longleaf emergence from the grass stage was not dependent on an RCD threshold, but on the degree of neighboring competition. Herbaceous weed control during the early establishment phase appears to be critical in accelerating height growth of longleaf pine seedlings in old fields.