Dry-Farming | Page 8

sub-humid district, which receives from 20 to
30 inches of rainfall annually; over the Rockies themselves, semiarid
conditions prevail; in the Great Basin, hemmed in by the Rockies on
the east and the Sierra Nevadas on the west, more arid conditions
predominate; to the west, over the Sierras and down to the seacoast,
semiarid to sub-humid conditions are again found.
Seasonal distribution of rainfall
It is doubtless true that the total annual precipitation is the chief factor
in determining the success of dry-farming. However, the distribution of
the rainfall throughout the year is also of great importance, and should
be known by the farmer. A small rainfall, coming at the most desirable
season, will have greater crop-producing power than a very much larger
rainfall poorly distributed. Moreover, the methods of tillage to be
employed where most of the precipitation comes in winter must be
considerably different from those used where the bulk of the
precipitation comes in the summer. The successful dry-farmer must
know the average annual precipitation, and also the average seasonal
distribution of the rainfall, over the land which he intends to dry-farm
before he can safely choose his cultural methods.
With reference to the monthly distribution of the precipitation over the
dry-farm territory of the United States, Henry of the United States
Weather Bureau recognizes five distinct types; namely: (1) Pacific, (2)
Sub-Pacific, (3) Arizona, (4) the Northern Rocky Mountain and Eastern
Foothills, and (5) the Plains Type:--
_"The Pacific Type.--_This type is found in all of the territory west of
the Cascade and Sierra Nevada ranges, and also obtains in a fringe of
country to the eastward of the mountain summits. The distinguishing
characteristic of the Pacific type is a wet season, extending from
October to March, and a practically rainless summer, except in northern
California and parts of Oregon and Washington. About half of the
yearly precipitation comes in the months of December, January, and
February, the remaining half being distributed throughout the seven
months--September, October, November, March, April, May, and
June."

_"Sub-Pacific Type.--_The term 'Sub-Pacific' has been given to that
type of rainfall which obtains over eastern Washington, Nevada, and
Utah. The influences that control the precipitation of this region are
much similar to those that prevail west of the Sierra Nevada and
Cascade ranges. There is not, however, as in the eastern type, a steady
diminution in the precipitation with the approach of spring, but rather a
culmination in the precipitation."
_"Arizona Type.--_The Arizona Type, so called because it is more fully
developed in that territory than elsewhere, prevails over Arizona, New
Mexico, and a small portion of eastern Utah and Nevada. This type
differs from all others in the fact that about 35 per cent of the rain falls
in July and August. May and June are generally the months of least
rainfall."
_"The Northern Rocky Mountain and Eastern Foothills Type.--_This
type is closely allied to that of the plains to the eastward, and the bulk
of the rain falls in the foothills of the region in April and May; in
Montana, in May and June."
_"The Plains Type.--_This type embraces the greater part of the
Dakotas, Nebraska, Kansas; Oklahoma, the Panhandle of Texas, and all
the great corn and wheat states of the interior valleys. This region is
characterized by a scant winter precipitation over the northern states
and moderately heavy rains during the growing season. The. bulk of the
rains comes in May, June, and July."
This classification emphasizes the great variation in distribution of
rainfall over the dry-farm territory of the country. West of the Rocky
Mountains the precipitation comes chiefly in winter and spring, leaving
the summers rainless; while east of the Rockies, the winters are
somewhat rainless and the precipitation comes chiefly in spring and
summer. The Arizona type stands midway between these types. This
variation in the distribution of the rainfall requires that different
methods be employed in storing and conserving the rainfall for crop
production. The adaptation of cultural methods to the seasonal
distribution of rainfall will be discussed hereafter.
Snowfall
Closely related to the distribution of the rainfall and the average annual
temperature is the snowfall. Wherever a relatively large winter
precipitation occurs, the dry-farmer is benefited if it comes in the form

of snow. The fall-planted seeds are better protected by the snow; the
evaporation is lower and it appears that the soil is improved by the
annual covering of snow. In any case, the methods of culture are in a
measure dependent upon the amount of snowfall and the length of time
that it lies upon the ground.
Snow falls over most of the dry-farm territory, excepting the lowlands
of California, the immediate Pacific coast, and other districts where the
average annual temperature is high. The heaviest snowfall is in the
intermountain district, from