The Phosphate Requirement of Barley at Different Periods of Growth

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Abstract
Experiments have been made in water cultures to test the effect of depriving barley plants of P after varying initial periods during which it had been supplied, and, contrariwise, of supplying P after initial periods of deprivation. The provision of phosphate for the first 6 weeks or longer permitted normal growth to be made, as was shown by the number of tillers, ears, and grains produced, the average number of grains per ear, and the dry weights. With shorter initial periods of phosphate supply, growth was seriously depressed in all these respects. If phosphate was withheld for the first 4 weeks, tiller production was not affected, but no ears were produced. With longer periods of initial deprivation growth was steadily depressed in all respects, and the type of growth gradually changed from a bushy succulent character to a thin, lanky, untillered plant bearing the travesty of an ear. The amount of phosphate absorbed by the plant increased steadily in more or less direct proportion to length of time phosphate was given at the beginning of growth, but sufficient was taken up in the first 6 weeks to enable the plant to make its maximum dry weight. The percentage of phosphate in dry matter rapidly increased from this time onwards. The absence of phosphate supply up to the first 6 weeks of growth caused an extremely rapid drop in the amount of phosphate ultimately taken up by the plant, after which a more gradual decrease occurred with lengthening periods of phosphate deprivation.

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