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
covered with a more or less dense growth of timber. This timbered
area roughly represents the mountainous and therefore the nonarable
portions of land. The same authority estimates that the desert-like
lands cover an area of 70,000,000 acres. Making the most liberal
estimates for mountainous and desert-like lands, at least one half
of the whole area, or about 600,000,000 acres, is arable land which
by proper methods may be reclaimed for agricultural purposes.
Irrigation when fully developed 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 a condition 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 one third of the whole surface receives above 20
inches of rainfall annually; one third receives from 10 to 20
inches, and one third receives less than lO inches. That is, about
1,267,000,000 acres in Australia are subject to reclamation by
dry-farming methods. 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 gives the 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
Total 100 per cent
Fifty-five per cent, or more than one half of the total land surface
of the earth, receives an annual precipitation of less than 20
inches, and must be reclaimed, if at all, by dry-farming. At least
10 per cent more receives from 20 to 30 inches under conditions that
make dry-farming methods necessary. 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 irrigation
systems 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.