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Abstract
Leaf nutrient analysis coupled with fertilizer applications are routinely used in commercial pecan production. Nitrogen can be applied in a range of formulations. However, definitive studies to establish nitrogen (N) uptake preference in pecan are lacking, as are definitive studies on the effects of N form on plant biomass production. In this study, we evaluated the effects of N form on plant growth and nutrient uptake in pecan (Carya illinoinensis Wangenh. K. Koch) using hydroponic cultures. Plants were grown under three N ratios of ammonium:nitrate (25 : 75, 50 : 50, and 75 : 25). Results from this study indicate that in-_creasing ammonium nutrition inhibited seedling growth. Plants grown with the 75 : 25 ratio (ammonium:nitrate) exhibited sig-_nificantly lower biomass, decreased root/shoot ratio, and lower specific leaf weight than observed in the other treatments. The highest root growth was observed in the 50 : 50 ratio treatment (ammonium:nitrate). Levels of calcium (Ca), magnesium (Mg), and manganese (Mn) in leaves were higher in plants grown under 25 : 75 (ammonium:nitrate) than in 75 : 25. Total N uptake on a dry weight basis was highest in the 75 : 25 ammonium:nitrate treatment. Plants exhibited preferential uptake of ammonium nitrogen under all nitrogen regimes. Ammonium nitrogen is generally applied in pecan orchard practices. This data suggest that further studies evaluating the effects of nitrogen form are warranted to determine if similar detrimental effects on pecan growth occur in the field. Such studies would be useful for optimizing current fertilization practices.