Effects of N Forms on Plant Growth and Fractions of Leaf N in Rabbiteye Blueberries

Abstract

The effects of N forms on the growth and concentrations of N fractions in plant parts were studied in order to evaluate the assimilating capability of rabbiteye blueberry plants f or NH₄ and NO₃. One-year-old rooted cuttings were grown in sand culture at 3 levels of N and at 3 levels of pH with NH₄, NH₄NO₃ or NO₃ as N sources.
The dry weight of plant tops was reduced at 14ppm N supplied as any of 3 N forms. At 56ppm and 140ppm N, NH₄NO₃-fed plants grew better than NH₄- and NO₃-fed ones. At pH 4 and 5.5, there was no difference of growth between NH₄-fed and NO₃- fed plants, but at pH 7 NH₄-fed plants were larger than NO₃-fed ones.
NH₄-fed plants had higher concentrations of total N and soluble N than NO₃-fed ones. In NH₄-fed plants, free NH₄ concentrations in leaves increased much more than amide-N concentrations as N supply was increased. In NO₃-fed plants NO₃ accumulated scantly in leaves and roots even at 140ppm N. NO₂ was not detected in any part of a plant.
These results showed that blueberry plants did not assimilate NH₄ efficiently nor absorb NO₃ sufficient for sustaining growth, which is distinctly different from such NH₄-loving plants as rice and tea.