Evaluating the nutritional status of Fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees using foliar analysis and DRIS application

Three studies were conducted with Fraser fir Christmas trees to determine the variation in foliar nitrogen (N) , phosphorus (P) , potassium (K), calcium (Ca), and magnesium (Mg) levels among plantation ages, sample locations within the crown, and effects due to seasonal changes. Extensive variation in nutrient concentrations existed with age of tissue collected, sample location with respect to aspect and vertical position, and normal seasonal fluctuation. Tree to tree nutrient variation indicated that greater sampling intensities are required for younger (under four years) plantations as opposed to older (over four years) plantations to achieve comparable confidence and precision levels. The data clearly illustrated that comparisons of foliar nutrient levels without regard to these sampling variables could cause erroneous diagnoses. Recommended foliar sampling practices involved sampling current-year's tissue from 2- or 3-year-old south-facing branches in October or November for routine foliar diagnoses.

Another study developed a DRIS application to evaluate N, P, K, Ca, and Mg nutrition on seventy-nine trees in a 3-year-old Fraser fir Christmas tree plantation. DRIS norms and index equations from premium grade Christmas tree were developed. In contrast to most crops where growth and yield are assessed, Fraser fir Christmas tree performance was evaluated by conventional grading procedures based on tree quality. A classification model utilizing several measured growth characteristics to predict Christmas tree grade was also investigated to objectively evaluate tree performance. Satisfactory grade-prediction results using a discriminant model were obtained yielding overall correct classification rates of 80 percent. Preliminary evaluation of DRIS performance suggested that assessments of nutritional balance, rather than examination of individual nutrient concentrations, may be more useful for prescribing fertilizer to improve Christmas tree quality.