The protein shows
the greatest variation. As the irrigation water is increased, the
percentage of protein decreases. In the case of wheat the variation
was over 9 per cent. The percentage of fat and nitrogen-free
extract, on the other hand, becomes larger as the water increases.
That is, crops grown with little water, as in dry-farming, are rich
in the important flesh-and blood-forming substance protein, and
comparatively poor in fat, sugar, stareh, and other of the more
abundant heat and fat-producing substances. This difference is of
tremendous importance in placing dry-farming products on the food
markets of the world. Not only seeds, tubers, and roots show this
variation, but the stems and leaves of plants grown with little
water are found to contain a higher percentage of protein than those
grown in more humid climates.
The direct effect of water upon the composition of plants has been
observed by many students. For instance, Mayer, working in Holland,
found that, in a soil containing throughout the season 10 per cent
of water, oats was produced containing 10.6 per cent of protein; in
soil containing 30 per cent of water, the protein percentage was
only 5.
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