Abstract:
Calcium deficiency in tomatoes was induced by adding ammonia nitrogen to the rooting medium. Ammonia was found to inhibit the absorption of calcium by the plant. When total soil nutrient concentration was varied, but the ratio of calcium to other ions held constant, blossom-end rot incidence was inversely related to the calcium level in fruits but was not necessarily associated with low calcium levels in leaves or whole plants. In the presence of high total salts, the incidence of the disorder could not be explained by a reduction in calcium content of whole plants and factors affecting distribution of the calcium within the plant were involved. The physiological disorder pith rot is described and evidence presented suggesting it is caused by a deficiency of calcium. Ammonia increased the incidence of the disorder but was not essential for its occurrence. In field trials on a red loam soil, ammonium sulphate reduced the pH values from 6.0 to 4.7, which prevented nitrification and induced pith rot and blossom-end rot through an accumulation of ammonia nitrogen. Calcium foliar sprays were able to offset yield reductions that were induced by moderate fertilizing with ammonium sulphate even where blossom-end rot did not occur. High total plant calcium was associated with reduced fruit yields.