style="margin-top: 7em">CHAPTER III

DRY-FARM AREAS—RAINFALL

The annual precipitation of rain and snow determines primarily the location of dry-farm areas. As the rainfall varies, the methods of dry-farming must be varied accordingly. Rainfall, alone, does not, however, furnish a complete index of the crop-producing possibilities of a country.

The distribution of the rainfall, the amount of snow, the water-holding power of the soil, and the various moisture-dissipating causes, such as winds, high temperature, abundant sunshine, and low humidity frequently combine to offset the benefits of a large annual precipitation. Nevertheless, no one climatic feature represents, on the average, so correctly dry-farming possibilities as does the annual rainfall. Experience has already demonstrated that wherever the annual precipitation is above 15 inches, there is no need of crop failures, if the soils are suitable and the methods of dry-farming are correctly employed. With an annual precipitation of 10 to 15 inches, there need be very few failures, if proper cultural precautions are taken. With our present methods, the areas that receive less than 10 inches of atmospheric precipitation per year are not safe for dry-farm purposes. What the future will show in the reclamation of these deserts, without irrigation, is yet conjectural.

Arid, semiarid, and sub-humid

Before proceeding to an examination of the areas in the United States subject to the methods of dry-farming it may be well to define somewhat more clearly the terms ordinarily used in the description of the great territory involved in the discussion.

The states lying west of the 100th meridian are loosely spoken of as arid, semiarid, or sub-humid states. For commercial purposes no state wants to be classed as arid and to suffer under the handicap of advertised aridity. The annual rainfall of these states ranges from about 3 to over 30 inches.

In order to arrive at greater definiteness, it may be well to assign definite rainfall values to the ordinarily used descriptive terms of the region in question. It is proposed, therefore, that districts receiving less than 10 inches of atmospheric precipitation annually, be designated arid; those receiving between 10 and 20 inches, semiarid; those receiving between 20 and 30 inches, sub-humid, and those receiving over 30 inches, humid. It is admitted that even such a classification is arbitrary, since aridity does not alone depend upon the rainfall, and even under such a classification there is an unavoidable overlapping. However, no one factor so fully represents varying degrees of aridity as the annual precipitation, and there is a great need for concise definitions of the terms used in describing the parts of the country that come under dry-farming discussions. In this volume, the terms "arid," "semiarid," "sub-humid" and "humid" are used as above defined.

Precipitation over the dry-farm territory

Nearly one half of the United States receives 20 inches or less rainfall annually; and that when the strip receiving between 20 and 30 inches is added, the whole area directly subject to reclamation by irrigation or dry-farming is considerably more than one half (63 per cent) of the whole area of the United States.

Eighteen states are included in this area of low rainfall. The areas of these, as given by the Census of 1900, grouped according to the annual precipitation received, are shown below:—

Arid to Semi-arid Group
Total Area Land Surface (Sq. Miles)

Arizona 112,920
California 156,172
Colorado 103,645
Idaho 84,290
Nevada 109,740
Utah 82,190
Wyoming 97,545
TOTAL 746,532

Semiarid to Sub-Humid Group

Montana 145,310
Nebraska 76,840
New Mexico 112,460
North Dakota 70,195
Oregon 94,560
South Dakota 76,850
Washington 66,880
TOTAL 653,095

Sub-Humid to Humid Group

Kansas 81,700
Minnesota 79,205
Oklahoma 38,830
Texas 262,290
TOTAL 462,025

GRAND TOTAL 1,861,652

The territory directly interested in the development of the methods of dry-farming forms 63 per cent of the whole of the continental United States, not including Alaska, and covers an area of 1,861,652 square miles, or 1,191,457,280 acres. If any excuse were needed for the lively interest taken in the subject of dry-farming, it is amply furnished by these figures showing the vast extent of the country interested in the reclamation of land by the methods of dry-farming. As will be shown below, nearly every other large country possesses similar immense areas under limited rainfall.

Of the one billion, one hundred and ninety-one million, four hundred and fifty-seven thousand, two hundred and eighty acres (1,191,457,280) representing the dry-farm territory of the United States, about 22 per cent, or a little more than one fifth, is sub-humid and receives between 20 and 30 inches of rainfall, annually; 61 per cent, or a little more than three fifths, is semiarid and receives between 10 and 20 inches, annually, and about 17 per cent, or a little less than one fifth, is arid and receives less than 10 inches of rainfall, annually.

These calculations are based upon the published average rainfall maps of the United States Weather Bureau. In the far West, and especially over the so-called "desert" regions, with their sparse population, meteorological stations are not numerous, nor is it easy to secure accurate data from them. It is strongly probable that as more stations are established, it will be found that the area receiving less than 10 inches of rainfall annually is considerably smaller than above estimated. In fact, the United States Reclamation Service states that there are only 70,000,000 acres of desert-like land; that is, land which does not naturally support plants suitable for forage. This area is about one third of the lands which, so far as known, at present receive less than 10 inches of rainfall, or only about 6 per cent of the total dry-farming territory.

In any case, the semiarid area is at present most vitally interested in dry-farming. The sub-humid area need seldom suffer from drouth, if ordinary well-known methods are employed; the arid area, receiving less than 10 inches of rainfall, in all probability, can be reclaimed without irrigation only by the development of more suitable. methods than are known to-day. The semiarid area, which is the special consideration of present-day dry-farming represents an area of over 725,000,000 acres of land. Moreover, it must be remarked that the full certainty of crops in the sub-humid regions will come only with the adoption of dry-farming methods; and that results already obtained on the edge of the "deserts" lead to the belief that a large portion of the area receiving less than 10 inches of rainfall, annually, will ultimately be reclaimed without irrigation.

Naturally, not the whole of the vast area just discussed could be brought under cultivation, even under the most favorable conditions of rainfall. A very large portion of the territory in question is mountainous and often of so rugged a nature that to farm it would be an impossibility. It must not be forgotten, however, that some of the best dry-farm lands of the West are found in the small mountain valleys, which usually are pockets of most fertile soil, under a good supply of rainfall. The foothills of the mountains are almost invariably excellent dry-farm lands. Newell estimates that 195,000,000 acres of land in the arid to sub-humid sections are