The Nutrition of Loblolly Pine Seedlings Exhibits Both Positive (Soil) and Negative (Foliage) Correlations with Seedling Mass

Sulfur and lime experiments at a sandy nursery in Texas detected no significant rate effect on height, root-collar diameter, or seedling mass of 1-0 loblolly pine (Pinus taeda L.) seedlings. Location of replications, however, had a large effect (P < 0.001) on seedling growth, which was related to nutrient levels in the soil. Positive correlations occurred between seedling height and the level of four macronutrients and three micronutrients in the soil. In contrast, due to carbohydrate dilution, negative correlations occurred between seedling mass and concentrations of nutrients (e.g., nitrogen and phosphorus) in needles. Height of seedlings at time of lifting was negatively related to foliar levels of aluminum and five other nutrients. In this study, low levels of organic matter (0.5 to 0.8 percent) and low levels of cation exchange capacity (0.9 to 1.9 meq 100 g–1) were not correlated with seedling morphology. It appears that applied fertilizers and inherent levels of soil nutrients affect seedling growth more than soil pH (3.6 to 6.3) or small changes in organic matter. Introduction Bareroot loblolly pine (Pinus taeda L.) seedlings are produced in nurseries with soils that vary in texture (South and Davey 1983). Coarse-textured soils with high sand content have advantages when it comes to sowing seed and lifting seedlings (South et al. 2016). As a result, most loblolly pine nurseries established after 1990 were established on soils with more than 85 percent sand. These soils typically retain fewer nutrients than fine-textured soils typical of nurseries established before 1960. Because coarse-textured soils typically have low cation exchange capacity (CEC), they require more fertilizer to achieve target seedling growth. Even so, Wakeley (1935: p. 37) said, “Fairly sandy soils frequently meet all forest nursery requirements if they are underlain by less pervious soils. The cost of enriching such soils with various fertilizers is offset by greater ease of working, and most pine species develop better root systems in light than heavy soils.” Although we have gained knowledge about seedling fertilization during the past century, much remains to be learned about nutrition of pine seedlings on sandy soils. Trials at a nursery in Texas revealed that applying sulfur or dolomitic lime had no significant effect on shoot or root growth of fertilized loblolly pine seedlings (South et al. 2017). Soil properties, however, varied greatly due to location of plots in the seedbed resulting in large seedling growth differences. We asked the question, if adding calcium, magnesium, or sulfur does not increase seedling mass, might differences in other nutrients account for observed differences in seedling size? The objectives of this investigation were to document the degree of soil nutrient variability in bareroot seedbeds and to compare seedling morphology with soil and foliar nutrition at time of lifting. Materials and Methods Two studies were established at the Richard O. Barham SuperTree Nursery (Bullard, TX). In March 2016, the soil was fumigated with a combination of chloropicrin and 1,3-dichloropropene. The trials were established on separate beds in the same field on a loamy sand soil (83:1:16 sand:silt:clay) with a CEC < 2.0 meq 100g–1. Stratified loblolly pine seed (half-sib family) were machine sown on April 16. The sulfur (S) trial was established on bed 7 and the lime trial was established on bed 3 (figure 1). On April 9, elemental S treatments (0, 813, 1,626 and 2,439 kg/ha) and pelletized dolomitic lime (90 percent passing 100 mesh sieve) treatments