I. Early loblolly pine stand response to tillage on the Piedmont and Upper Coastal Plain of Georgia: Mortality, stand uniformity, and second and third year growth

Abstract

The effects of machine planting, disking, bedding, and bedding + subsoiling on growth of loblolly pine (Pinus taeda L.) were assessed after two and three growing seasons for seven contrasting sites on the Piedmont and Upper Coastal Plain of Georgia. Heights and groundline diameters of half the trees (50 trees) per plot, percent mortality, individual tree volume index (D2H), stand uniformity, and per hectare volume index were compared across sites and treatments. Average tree size of the treatments were ranked (from largest to smallest) bed, bed + subsoil, disk, machine, and no-till. At the end of the third growing season, the trees in the bed only treatment had a mean height, groundline diameter, and volume index of 2.3 m ± 0.06 SE, 59 mm ± 1.7 SE, and 0.0094 m3 ± 0.00066 SE, respectively. The trees of the no-till treatment had a mean height, groundline diameter, and volume index of 2.1 m ± 0.07 SE, 50 mm ± 1.6 SE, and 0. 0063 m3 ± 0.00056 SE, respectively. Overall, the disk, bed, and bed + subsoil treatment plots had significantly greater absolute volume growth during the third growing season than the no-till and machine plots. Most of the tree mortality within all treatments occurred during the first growing season with the disk treatment having the least mortality (13.6%) and the no-till treatment the most (24.9%). Stand height and diameter uniformity, examined using the within plot coefficient of variation, was not significantly different among treatments. Per hectare volume index was significantly greater for the bed (7.0 m3/ha) and bed + subsoil treatments (7.1 m3/ha) than for the no-till (4.5 m3/ha) and machine (5.2 m3/ha) treatments. Significant differences occurred between sites for tree size parameters, ranging between 2.7 m mean height and 64 mm mean groundline diameter for a site on a Cowarts soil series to 1.8 m mean height and 45 mm mean groundline diameter for trees growing on a Pacolet soil series. Significant interactions between tillage treatments and sites occurred for some tree size parameters at age 2, but not age 3, and for average plot mortality rate. The results of this study indicate that some early gains in tree growth can be achieved through soil tillage on upland sites. Bedding provided the most consistent, positive response, but adding subsoiling to bedding provided no benefit. Overall, the gains were relatively small and site dependent. Tillage on these Piedmont and Upper Coastal Plain soils should best be considered as part of a complete management program that includes to weed control and fertilization. South. J. Appl. For. 26(4).