FLUORINE TOXICITY IN TOMATO AS MODIFIED BY ALTERATIONS IN THE NITROGEN, CALCIUM, AND PHOSPHORUS NUTRITION OF THE PLANT

Abstract

The effects of varied N, Ca, and P nutrition on the susceptibility of tomato plants to injury from NaF applns. to the roots and HF fumigation of the tops of the plants are summarized as follows:[long dash]Typical symptoms of F toxicity consisting of tip and marginal scorching of the younger fuller expanded leaves were identical with either treatment. Medium levels of N, Ca, and P favored absorption and translocation of F in sufficient quantities to cause ties of F in plants fumigated at the higher F level. A deficient supply of N, Ca, and P reduced the absorption of F through the roots or leaves. Excessive amts. of N and Ca also prevented F injury. Where Ca was added to the substrate in concns. above 40 ppm., its tendency to precipitate F in the form of insoluble compounds within or around the roots further reduced injury to the foliage. Severe F toxicity of the leaves was associated with the highest F content of foliage in the root F treatment. This was not so marked in the fumigated series. Root injury occurred in the same plants which showed foliage injury in the root-treated series, but there was no indication of F injury to roots as a result of fumigation. Root injury was not associated with a high F content, many of the highest F values occurring within the healthiest root systems. When NaF was added to the substrate, although F was translocated to the leaves, the roots almost invariably showed a greater F accumulation than did the leaves. In contrast, fumigated plants showed a high accumulation of F in the leaves and a normal amt. in the roots, suggesting the absence of downward translocation of F from the leaves. The avg. F content of tomato leaves as a result of fumigation at 0.048 ppm. F was 40 ppm., whereas at the 0.47 ppm. F fumigation level the avg. was 477 ppm. with definite injury.