The moisture content of dry-farm wheat, the chief dry-farm crop, is even more important. According to Wiley the average water content of wheat for the United States is 10.62 per cent, ranging from 15 to 7 per cent. Stewart and Greaves examined a large number of wheats grown on the dry-farms of Utah and found that the average per cent of water in the common bread varieties was 8.46 and in the durum varieties 8.89. This means that the Utah dry-farm wheats transported to ordinary humid conditions would take up enough water from the air to increase their weight one fortieth, or 2.2 per cent, before they reached the average water content of American wheats. In other words, 1,000,000 bushels of Utah dry-farm wheat contain as much nutritive matter as 1,025,000 bushels of wheat grown and kept under humid conditions. This difference should be and now is recognized in the prices paid. In fact, shrewd dealers, acquainted with the dryness of dry-farm wheat, have for some years bought wheat from the dry-farms at a slightly increased price, and trusted to the increase in weight due to water absorption in more humid climates for their profits. The time should be near at hand when grains and similar products should be purchased upon the basis of a moisture test.
While it is undoubtedly true that dry-farm crops are naturally drier than those of humid countries, yet it must also be kept in mind that the driest dry-farm crops are always obtained where the summers are hot and rainless. In sections where the precipitation comes chiefly in the spring and summer the difference would not be so great. Therefore, the crops raised on the Great Plains would not be so dry as those raised in California or in the Great Basin. Yet, wherever the annual rainfall is so small as to establish dry-farm conditions, whether it comes in the winter or summer, the cured crops are drier than those produced under conditions of a much higher rainfall, and dry farmers should insist that, so far as possible in the future, sales be based on dry matter.
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.
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 5.6 per cent, and in soil containing 70 per cent of water, it was only 5.2 per cent. Carleton, in a study of analyses of the same varieties of wheat grown in humid and semi-arid districts of the United States, found that the percentage of protein in wheat from the semiarid area was 14.4 per cent as against 11.94 per cent in the wheat from the humid area. The average protein content of the wheat of the United States is a little more than 12 per cent; Stewart and Greaves found an average of 16.76 per cent of protein in Utah dry-farm wheats of the common bread varieties and 17.14 per cent in the durum varieties. The experiments conducted at Rothamsted, England, as given by Hall, confirm these results. For example, during 1893, a very dry year, barley kernels contained 12.99 per cent of protein, while in 1894, a wet, though free-growing year, the barley contained only 9.81 per cent of protein. Quotations might be multiplied confirming the principle that crops grown with little water contain much protein and little heat-and fat-producing substances.
Climate and composition
The general climate, especially as regards the length of the growing season and naturally including the water supply, has a strong effect upon the composition of plants. Carleton observed that the same varieties of wheat grown at Nephi, Utah, contained 16.61 per cent protein; at Amarillo, Texas, 15.25 per cent; and at McPherson, Kansas, a humid station, 13.04 per cent. This variation is undoubtedly due in part to the varying annual precipitation but, also, and in large part, to the varying general climatic conditions at the three stations.