Controlling loblolly pine seedling growth through carbon metabolism regulation rather than mechanical procedures
Nursery soils should be managed to maintain desirable ranges in essential plant nutrients, organic matter, and available water for the species being produced.In many cases, however, soil fertility and available water far exceed the amounts needed to produce loblolly pine seedlings of the size range required for artificial regeneration. Top clipping and root pruning or wrenching are typically used to restrict seedling development to target ranges. Clipping, however, significantly modifies seedling morphology and prevents quality estimation with Wakeley's morphological grades.Reducing baseline soil fertility and total top dressing did not consistently produce seedlings with reasonable height and root collar diameters.In almost all cases, seedling height and diameter exceeded planting restrictions.Research in carbon metabolism revealed that the seasonal growth patterns for loblolly pine seedling tops and roots are quite different. Top growth is active through summer and early fall whereas root growth dominates in fall and early winter.It is, therefore, possible to regulate either top or root development by the timing and amount of N and water application.In essence, we recommend controlling seedling development by regulating carbon metabolism. Our approach is cheaper than mechanical means and results in early and consistent bud development, and a more uniform and natural top/root ratio.In traditionally operated nurseries genetically noncompetitive seedlings have the chance to grow to a reasonable size, but these seedlings do not perform well after outplanting. With our protocols, these noncompetitive seedlings are easily identified at lifting.Our protocols reduce water use and the risk of ground and surface water contamination caused by excess fertilization, especially with nitrates.