Effects of early release on natural versus container loblolly pines 12 years after field establishment. II. Early loblolly pine stand response to tillage on the Piedmont and Upper Coastal Plain of Georgia: Tree allometry, foliar nitrogen concentration, soil bulk density, soil moisture, and soil nitrogen status

The effects of machine planting, disking, bedding, and bedding + subsoiling on the allometry and foliar nitrogen status of 3-yr-old loblolly pine trees (Pinus taeda L) and soil properties were assessed for a range of sites on the Piedmont and Upper Coastal Plain of Georgia. The objective of the study was to determine the effect of these soil tillage practices on the mechanisms that drive stand growth differences that result from site preparation. Although tillage increased growth, the tillage treatments studied did not appear to affect plant biomass partitioning between roots and shoots or foliar nitrogen concentration. Increased available soil N, measured from a one-time estimate of available N and laboratory incubation, was not related to the observed increase in tree growth. Extractable NH4 from the soil on the slowest growing, no-till treatment trees was significantly greater than those of the other treatments. No treatment differences were found for total soil N, extractable NO3, or total N mineralized. Bulk density and soil moisture were lower on the beds and in the disk plots, the treatments with the greatest growth. Therefore, soil N availability, foliar N concentrations, and biomass partitioning did not appear to drive the tillage mediated growth differences. Rather, improved soil physical conditions likely resulted in a greater volume of soil exploited and hence, larger trees.