Critical calcium concentrations in radish grown under various regimes of nitrogen nutrition

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Abstract
Ammonium nutrition of radish plants (Raphanus sativus L.) suppresses their accumulation of Ca. The objective of this study was to determine the critical Ca concentration of radish in order to assess if NH4 + nutrition induces Ca deficiency in this crop. Cultivar Cherry Belle was grown in sand culture in a greenhouse. Nitrogen was provided as nitrate or ammonium salts, and Ca was varied from 1 to 200 mg/liter in solution. With N03’ nutrition, plant growth increased curvilinearly with increased Ca in solution. Calcium accumulation in shoots was a good index of relative root (edible radish) growth. The critical Ca concentration in shoots for optimum root growth was 2% of the dry matter. With NH4+ nutrition, plant growth declined linearly with increased Ca in solution and with Ca accumulation in the shoots. A critical Ca concentration could not be determined for plants grown with NH4 + nutrition. The antagonism between Ca and NH4 + nutrition could not be explained by deficiencies or toxicities of other elements.