Ammonium and nitrate concentrations as factors in tomato growth and nutrient uptake

Tomato plants were grown in sand culture with NH4 or NO3 at 14, 56, or 112 ppm N in solution. Plants supplied with NH4 at 112 ppm N developed ammonium toxicity symptoms and produced one‐third the dry weight of NO3 fed plants. In contrast, plants receiving NH4 at 14 ppm N appeared normal and had dry weight slightly higher than with NO3 at the same concentration. As NH4 concentration increased from 14 to 112 ppm N, plant growth, K, Ca, and Mg contents decreased while soluble NH4, in the tissue was greatly increased.