[Illustration: FIG. 163.--Water cultures of buckwheat: 1, with all the
food elements; 2, without potash; 3, without nitrates.]
The quantity of fertilizer needed by the farmers of the world is
enormous, and the problem of securing the necessary substances in
quantities sufficient to satisfy the demand bids fair to be serious.
But modern chemistry is at work on the problem, and already it is
possible to make some nitrogen compounds on a commercial scale. When
nitrogen gas is in contact with heated calcium carbide, a reaction
takes place which results in the formation of calcium nitride, a
compound suitable for enriching the soil. There are other commercial
methods for obtaining nitrogen compounds which are suitable for
absorption by plant roots.
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