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Diagnosis and Recommendation Integrated System Modifications for Fraser Fir Christmas Trees

Dep. of Forestry, 228 Cheatham Hall, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061-0324

*Corresponding author.

ABSTRACT

The Diagnosis and Recommendation Integrated System (DRIS) has been used successfully to diagnose the nutrition of many crops. Some practioners, however, cite problems in applying DRIS to certain crops. Among the problems are: identifying a suitable expression of yield, maintaining symmetry in DRIS index equations, and dealing with extremely variable micronutrients. The purpose of this study was to resolve problems as they were encountered in applying DRIS to Fraser fir (Abies fraseri [Pursh] Poir.) Christmas trees. A total of 107 Fraser fir plantations were sampled for foliage, soil, and diameter measurements. Foliage was analyzed for N, P, K, Ca, Mg, Zn, Mn, Fe, Cu, and B. Age-adjusted diameter was used successfully as the growth-response variable. The DRIS symmetry was maintained by including nonsignificant ratios, but setting their standardization functions equal to zero. This reduced the influence of the nondiscriminating nutrient ratios on the DRIS analysis. Norm ranges, as opposed to discrete norms, were used successfully to correct for the influence of extremely variable micronutrient ratios on the DRIS analysis. This combination of adaptations and modifications of DRIS should greatly enhance its use for this tree crop.

Research sponsored by the H. Smith Richardson Trust.

Received for publication June 11, 1990.