Growth and Composition of Radish under Various Regimes of Nitrogen Nutrition

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Abstract
In greenhouse studies with radish (Raphanus sativus L.), KNO3, (NH4)2SO4, urea, dried sewage sludge, and dried cow manure were applied at 200, 400, and 800 mgN/1,200 g soil with 0 or 10 ppm of nitrapyrin. Soil analysis for pH, and indicated that nitrification was inhibited throughout the growth (38 days) of the plants. Nitrogen deficiency limited plant growth at the 2 low rates of application of organic fertilizers. With the ammoniacal fertilizers, toxicity restricted root and shoot growth at the highest rate of N and especially in the presence of nitrapyrin relative to the KNO3 regimes. An interaction of nitrapyrin with the organic fertilizers limited root growth. This restriction was attributed partially to toxicity. Some indication of nitrapyrin toxicity was suggested by plant foliar appearance with the organic fertilizers but not with the inorganic sources. Ca and Mg concentrations varied with treatment, with increased rate of N and nitrapyrin addition sharply restricting their accumulation, especially with the ammoniacal and organic fertilizers. Percentage of K in the plants changed in a reciprocal manner to that of Ca or Mg. Compositional changes suggested that toxicity was a major factor causing a limitation of growth with the combination of nitrapyrin with ammoniacal or organic fertilizers.

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