THE annual precipitation of rain and snow determinesprimarily the location of dry-farm areas. As the rainfall varies, the methods ofdry-farming must be varied accordingly. Rainfall, alone, does not, however, furnisha complete index of the crop-producing possibilities of a country.
The distribution of the rainfall, the amountof snow, the water-holding power of the soil, and the various moisture-dissipatingcauses, such as winds, high temperature, abundant sunshine, and low humidity frequentlycombine to offset the benefits of a large annual precipitation. Nevertheless, noone climatic feature represents, on the average, so correctly dry-farming possibilitiesas does the annual rainfall. Experience has already demonstrated that wherever theannual precipitation is above 15 inches, there is no need of crop failures, if thesoils are suitable and the methods of dry-farming are correctly employed. With anannual precipitation of 10 to 15 inches, there need be very few failures, if propercultural precautions are taken. With our present methods, the areas that receiveless than 10 inches of atmospheric precipitation per year are not safe for dry-farmpurposes. What the future will show in the reclamation of these deserts, withoutirrigation, is yet conjectural.
Arid, semiarid, and sub-humid
Before proceeding to an examination of the areasin the United States subject to the methods of dry-farming it may be well to definesomewhat more clearly the terms ordinarily used in the description of the great territoryinvolved in the discussion.
The states lying west of the 100th meridian areloosely spoken of as arid, semiarid, or sub-humid states. For commercial purposesno state wants to be classed as arid and to suffer under the handicap of advertisedaridity. The annual rainfall of these states ranges from about 3 to over 30 inches.
In order to arrive at greater definiteness, itmay be well to assign definite rainfall values to the ordinarily used descriptiveterms of the region in question. It is proposed, therefore, that districts receivingless than 10 inches of atmospheric precipitation annually, be designated arid; thosereceiving 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 sucha 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 describingthe 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 receives20 inches or less rainfall annually; and that when the strip receiving between 20and 30 inches is added, the whole area directly subject to reclamation by irrigationor dry-farming is considerably more than one half (63 per cent) of the whole areaof the United States.
Eighteen states are included in this area oflow rainfall. The areas of these, as given by the Census of 1900, grouped accordingto the annual precipitation received, are shown below:-
Arid to Semi-arid Group
Total Area Land Surface (Sq. Miles)
Semiarid to Sub-Humid Group
Sub-Humid to Humid Group
The territory directly interested in the developmentof the methods of dry-farming forms 63 per cent of the whole of the continental UnitedStates, not including Alaska, and covers an area of 1,861,652 square miles, or 1,191,457,280acres. If any excuse were needed for the lively interest taken in the subject ofdry-farming, it is amply furnished by these figures showing the vast extent of thecountry interested in the reclamation of land by the methods of dry-farming. As willbe shown below, nearly every other large country possesses similar immense areasunder limited rainfall.
Of the one billion, one hundred and ninety-onemillion, 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 alittle more than one fifth, is sub-humid and receives between 20 and 30 inches ofrainfall, annually; 61 per cent, or a little more than three fifths, is semiaridand receives between 10 and 20 inches, annually, and about 17 per cent, or a littleless than one fifth, is arid and receives less than 10 inches of rainfall, annually.
These calculations are based upon the publishedaverage rainfall maps of the United States Weather Bureau. In the far West, and especiallyover the so-called "desert" regions, with their sparse population, meteorologicalstations are not numerous, nor is it easy to secure accurate data from them. It isstrongly probable that as more stations are established, it will be found that thearea receiving less than 10 inches of rainfall annually is considerably smaller thanabove estimated. In fact, the United States Reclamation Service states that thereare only 70,000,000 acres of desert-like land; that is, land which does not naturallysupport 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 about6 per cent of the total dry-farming territory.
In any case, the semiarid area is at presentmost vitally interested in dry-farming. The sub-humid area need seldom suffer fromdrouth, if ordinary well-known methods are employed; the arid area, receiving lessthan 10 inches of rainfall, in all probability, can be reclaimed without irrigationonly by the development of more suitable. methods than are known to-day. The semiaridarea, which is the special consideration of present-day dry-farming represents anarea of over 725,000,000 acres of land. Moreover, it must be remarked that the fullcertainty of crops in the sub-humid regions will come only with the adoption of dry-farmingmethods; 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 inchesof rainfall, annually, will ultimately be reclaimed without irrigation.
Naturally, not the whole of the vast area justdiscussed could be brought under cultivation, even under the most favorable conditionsof rainfall. A very large portion of the territory in question is mountainous andoften of so rugged a nature that to farm it would be an impossibility. It must notbe forgotten, however, that some of the best dry-farm lands of the West are foundin the small mountain valleys, which usually are pockets of most fertile soil, undera good supply of rainfall. The foothills of the mountains are almost invariably excellentdry-farm lands. Newell estimates that 195,000,000 acres of land in the arid to sub-humidsections are covered with a more or less dense growth of timber. This timbered arearoughly represents the mountainous and therefore the nonarable portions of land.The same authority estimates that the desert-like lands cover an area of 70,000,000acres. Making the most liberal estimates for mountainous and desert-like lands, atleast one half of the whole area, or about 600,000,000 acres, is arable land whichby proper methods may be reclaimed for agricultural purposes. Irrigation when fullydeveloped may reclaim not to exceed 5 per cent of this area. From any point of view,therefore, the possibilities involved in dry-farming in the United States are immense.
Dry-farm area of the world
Dry-farming is a world problem. Aridity is acondition met and to be overcome upon every continent. McColl estimates that in Australia,which is somewhat larger than the continental United States of America, only onethird of the whole surface receives above 20 inches of rainfall annually; one thirdreceives from 10 to 20 inches, and one third receives less than l O inches. Thatis, about 1,267,000,000 acres in Australia are subject to reclamation by dry-farmingmethods. This condition is not far from that which prevails in the United States,and is representative of every continent of the world. The following table givesthe proportions of the earth's land surface under various degrees of annual precipitations:--
|Annual Precipitation ||Proportion of Earth's Land Surface |
|Under 10 inches ||25.0 per cent |
|From 10 to 20 inches ||30.0 per cent |
|From 20 to 40 inches ||20.0 per cent |
|From 40 to 60 inches ||11.0 per cent |
|From 60 to 80 inches ||9.0 per cent |
|From 100 to 120 inches ||4.0 per cent |
|From 120 to 160 inches ||0.5 per cent |
|Above 160 inches ||0.5 per cent |
|100 per cent |
Fifty-five per cent, or more than one half ofthe total land surface of the earth, receives an annual precipitation of less than20 inches, and must be reclaimed, if at all, by dry-farming. At least 10 per centmore receives from 20 to 30 inches under conditions that make dry-farming methodsnecessary. A total of about 65 per cent of the earth's land surface is, therefore,directly interested in dry-farming. With the future perfected development of irrigationsystems and practices, not more than 10 per cent will be reclaimed by irrigation.Dry-farming is truly a problem to challenge the attention of the race.