The nutritive substances in crops

The dry matter of all plants and plant parts consists of three very distinct classes of substances:  First, ash or the mineral constituents.  Ash is used by the body in building bones and in supplying the blood with compounds essential to the various life processes.  Second, protein or the substances containing the element nitrogen.  Protein is used by the body in making blood, muscle, tendons, hair, and nails, and under certain conditions it is burned within the body for the production of heat.  Protein is perhaps the most important food constituent.  Third, non-nitrogenous substances, including fats, woody fiber, and nitrogen-free extract, a name given to the group of sugars, starehes, and related substances.  These substances are used by the body in the production of fat, and are also burned for the production of heat.  Of these valuable food constituents protein is probably the most important, first, because it forms the most important tissues of the body and, secondly, because it is less abundant than the fats, starches, and sugars.  Indeed, plants rich in protein nearly always command the highest prices.

The composition of any class of plants varies considerably in different localities and in different seasons.  This may be due to the nature of the soil, or to the fertilizer applied, though variations in plant composition resulting from soil conditions are comparatively small.  The greater variations are almost wholly the result of varying climate and water supply.  As far as it is now known the strongest single factor in changing the composition of plants is the amount of water available to the growing plant.

Variations due to varying water supply

The Utah station has conducted numerous experiments upon the effect of water upon plant composition.  The method in every case has been to apply different amounts of water throughout the growing season on contiguous plats of uniform land. [Lengthy table deleated from this edition.] Even a casual study of . . . [the results show] that the quantity of water used influenced the composition of the plant parts.  The ash and the fiber do not appear to be greatly influenced, but the other constituents vary with considerable regularity with the variations in the amount of irrigation water.  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.