Tomato plants ‘Campbell 1327’ grown in peat with NH 4 nutrition had no visible symptoms of NH 4 toxicity, while severe symptoms of NH 4 toxicity were displayed in solution or sand culture. Growth of plants was much better with NO 3 -N than NH 4 -N in sand, vermiculite, or solution culture; but in peat, growth of NH 4 -treated plants equalled or exceeded that of NO 3 -treated plants in sand, vermiculite, and peat. The total dry weight of NH 4 -treated plants grown in peat was 2, 2.5, and 3.4 times higher than plants grown in vermiculite, sand, and solution culture, respectively. Content of uncomplexed ASHS.109.3.406 in NH 4 -treated plants grown in peat was reduced markedly compared with other media. NH 4 -treated plants grown in sand, vermiculite, and solution culture, displaying NH 4 toxicity symptoms, had a total amino acid:free NH 4 + molar ratio < 2, compared to 6-8 with NO 3 . For NH 4 -treated plants grown in peat the ratio was similar to that of NO 3 -treated plants. Asparagine and glutamine in NH 4 -treated plants grown in peat were 3.5 and 11.3 times higher than with NO 3 -N, indicating a high efficiency in detoxification of NH 4 through incorporation into these amino acids. The medium on which a plant is grown can have a marked influence on the plant response to N form.
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Magalhães et al. (1984) studied this question.