Effect of Nitrogen Form and pH on Growth, NO3-N, NH4-N and Total N Content of Container-grown Doublefile Viburnum1

Doublefile viburnums ( Viburnum plicatum Miq. tomentosum Thunb.) were cultured at 2 pH ranges, 3 to 4 and 7 to 8, with 3 N treatments (NO 3 -N, NH 4 -N, or NO 3 -N plus NH 4 -N) supplied daily at a concentration of 1.5 meq N per pot. Fresh weights of shoots and roots from plants grown with NH 4 -N at pH 3 to 4 were significantly lower than from plants grown with other N treatments. Plants developed leaf necrosis and ultimately died when grown with NH 4 -N at pH 3 to 4. Limited leaf necrosis developed on other NH 4 -N treated plants. Leaf necrosis did not develop on leaves of plants grown with NO 3 -N at pH 3 to 4 or 7 to 8. Roots of all plants, except those grown with NH 4 -N at pH 3 to 4 appeared vigorous and healthy. Nitrate N was greatest in shoots of NO 3 -N treated plants. Shoot NH 4 -N levels were greatest in NH 4 -N treated plants and correlated with the severity of leaf necrosis. Total N concentration in shoots and roots were greatest in plants grown with NO 3 -N at pH 3 to 4 and NO 3 -N plus NH 4 -N at pH 3 to 4. In the growing medium, NO 3 -N predominated at the high pH range; NH 4 -N at the lower pH range. The N form and pH of the growing medium exerted marked effects on growth, and on N availability and utilization by viburnum.