Abstract
IN the early post-bloom period it is common to spray apple trees with a 0.5 per cent urea solution which, when repeated several times, results in a clear increase of leaf chlorophyll and leaf total nitrogen in comparison with leaves of unsprayed trees1. Higher concentrations may cause leaf injury. It seems unlikely that this injury caused in the late autumn would reduce to any extent the total amount photosynthesized during the passing season. This would permit the use of comparatively concentrated spray solutions at that time. The absorption of nitrogen may be proportional to the concentration of the urea solution2.
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References
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OLAND, K. Nitrogen Feeding of Apple Trees by Post-Harvest Urea Sprays. Nature 185, 857 (1960). https://doi.org/10.1038/185857a0
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DOI: https://doi.org/10.1038/185857a0
