A Comparison of Various Means of Testing the Effectiveness of Foliar Sprays for Correcting Zinc Deficiencies in Citrus Trees

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Abstract
Four zinc compounds were applied as foliar sprays for correcting zinc deficiency in a young Shamouti orange orchard. The effectiveness of the various treatments was tested by assessing visual deficiency symptoms, by determining zinc in the leaves and by carbonic anhydrase assay both in the sprayed leaves and in the new, unsprayed flush. Zinc determinations showed high levels of zinc in the sprayed leaves and deficient levels in the new flush. The zinc values were, nevertheless, related to visual symptoms towards the end of the observation period. Carbonic anhydrase activity in the sprayed leaves was closely related to the course of visual recovery of the trees. The enzyme activity in the sprayed leaves did not reach normal levels and thus showed less difference between the sprayed and unsprayed leaves than did the zinc determinations. The merits of carbonic anhydrase assays for evaluating the effectiveness of zinc foliar sprays are discussed in the light of these results.

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