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Evaluating Soil and Foliar Fertilization of Abies nordmanniana Under Container and Field Production

Abstract Considerable debates exist about the efficacy of foliar application of nutrients to Christmas trees, but little research has been conducted to determine whether this method of fertilization is beneficial. In this study, standard foliar and soil-applied fertilization products were applied to Nordmann fir Christmas trees under greenhouse and field-grown management regimes. On both sites, foliar nitrogen (N) and boron (B) concentrations, color, and normalized difference vegetation index (NDVI) were evaluated. Plant growth and needle chlorophyll/carotenoids were also monitored at the greenhouse site and sulfur (S) at the field site. At all sites, the soil-applied fertilizers were effective in increasing foliar N% compared to untreated and foliar applications. The foliar-applied products did not improve foliar N% compared to untreated trees. Foliar B concentrations were correlated with foliar fertilizer applications, indicating that B can be absorbed via foliar application. A second part of this study investigated alternate or complementary methods of assessing foliar N%. We addressed whether plant color, spectral reflectance, chlorophyll measures, or NDVI measurements could serve as surrogates for foliar N%. Color, chlorophyll/carotenoid, and foliar N% were closely correlated. However, NDVI evaluations showed no relationship with foliar N%, color, or chlorophyll/carotenoid levels.