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- Author or Editor: F. H. Sutherland x
Abstract
Bearing ‘Valencia’ orange trees growing in a commercial orchard adjacent to a known source of fluoride air pollution were sprayed periodically over a 3-year period with Ca(OH)2 and CaCl2 sprays. These materials in spray and dust forms have been used successfully in the Pacific Northwest to protect gladiolus and peaches from the harmful effects of fluoride-containing atmospheres. It has been postulated that calcium reacts with fluoride gases to produce insoluble and therefore nontoxic CaF2.
Results of these studies indicated that under conditions of high fluoride air pollution, application of lime sprays may improve citrus fruit production, but the mechanism of protection or improvement was not as simple as previously postulated. Immediately adjacent to the source where fluoride air pollution was at a maximum, applications of both Ca(OH)2 and CaCl2 were associated with increased internal fluoride accumulation by ‘Valencia’ orange foliage. With increased distance and therefore diminishing air pollution, an apparent reversal in effect was observed with the calcium sprays resulting in reduced internal accumulation of fluoride.
Although the effects of CaCl2 sprays on fluoride accumulation closely paralleled those obtained with Ca(OH)2, fruit production was not improved where CaCl2 sprays were applied, possibly as a result of induced chloride toxicity.
Abstract
‘Valencia’ orange trees subjected to a drenching shower twice a week or sprinkled daily with a fine water spray until their leaf surfaces were thoroughly wet were found to accumulate less fluoride than unsprayed trees when exposed to low concentrations of HF gas. In the early stages of leaf development the drenching shower and light sprinkling treatments were equally effective in reducing fluoride uptake. After the foliage was 3 or 4 months old, however, the daily sprinklings had little effect on fluoride uptake whereas the twice weekly 1 hr drenchings effectively prevented fluoride accumulation. Growth responses were inversely proportional to fluoride uptake with maximum growth suppression associated with maximum fluoride uptake. After 9 months of treatment, the drenchings had reduced fluoride uptake by 85% and growth suppression by approximately 87%. In the same period the daily sprinkling treatment had reduced fluoride uptake by 37% and growth suppression by 45%.