Nitrogen Form and Solution pH Influence Growth and Nutrition of Two Vaccinium Clones

The effects of pH and N form on growth and nutrition of blueberry (Vaccinium corymbosum L. × V. angustifolium Ait. cv . Northblue) and cranberry (V. macrocarpon Ait. cv . Searles) were tested in separate greenhouse hydroponic experiments. A factorial treatment arrangement of two pH levels (4.5 and 6.5) and three N forms (NO 3 -N, NH 4 -N, and NH 4 -N/NO 3 -N) was used for each clone. Blueberry shoot growth and final dry weight were greatest at pH 4.5, regardless of N form. In contrast, cranberry fresh weight accumulation and final dry weight were higher with NH 4 -N/NO 3 -N or NH 4 -N than with NO 3 -N alone. Cranberry plants receiving NO 3 -N alone accumulated low levels of tissue N and grew relatively poorly at both pH levels. Differences in N response by these two species may be due partially to the environments in which they were selected. Soil from the site where `Northblue' blueberry was selected contained relatively high NO 3 -N and low NH 4 -N levels; soil from commercial `Searles' cranberry bogs had relatively low NO 3 -N and high NH 4 -N levels. Both species accumulated relatively high levels of root Fe, regardless of pH or N form. Levels of Fe in the root were as much as 100 times higher than in the shoot. Based on X-ray microanalysis of cranberry roots, most of the Fe appeared to be precipitated on the root surface as iron phosphate. Concentrations of Mn in shoots and roots depended on N form and pH. In general, root Mn was highest at pH 6.5 and apparently was precipitated with Fe.