Christmas Tree Response to N Fertilization and the Development of Critical Foliar N Levels in New York
The effectiveness of fertilization as a tool to increase growth rate and quality of Christmas trees depends on the ability to identify trees that are limited by nutrition. Foliar analysis is one approach to identify nutrition-limited trees, but it requires pre-established diagnostic criteria for application. The objective of this study was to assess growth response of Christmas trees to N fertilizer, and to develop critical foliar N levels for species commonly grown in New York. We evaluated diameter growth and foliar N concentration response of balsam fir (Abies balsamea [L.] Mill.), Canaan fir (Abies balsamea var. phanerolepis [Fern.]), Fraser fir (Abies fraseri [Pursh] Poir.), concolor fir (Abies concolor [Gord. and Glend.] Lindl.), and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) midrotation Christmas trees to N fertilization on 11 sites distributed across central New York. Two fertilizer treatments were applied: 1 oz N tree−1 as ammonium nitrate (AN) and chicken manure compost (CMC) applied at 0.6 oz N tree−1. Current annual diameter increment (CAI) for Canaan fir, Fraser fir, and Douglas-fir increased in response to AN. Two-year CAI for AN-treated trees was greater than control trees for all species with the exception of Canaan fir. Application of CMC had no effect on CAI the first year after application but did increase 2-year CAI for concolor and Fraser fir. Vector analysis, which simultaneously displays foliar mass, N concentration, and N content, indicated that all species responded positively to AN in more than 50% of the cases (with the exception of Canaan fir). Foliar response to CMC was weak, exhibiting a positive response in only 38% of the cases. Based on the foliar response of trees to AN, the following critical foliar N concentrations are proposed for Christmas trees in New York: balsam fir, 1.65%; concolor fir, 1.75%; Canaan fir, 1.60%; Douglas-fir, 1.45%; and Fraser fir, 1.60%.
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