Dry-Farming | Page 8

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 the west slope of the Sierra Nevadas to the east slope of the Rockies. The degree of snowfall on the agricultural lands is very variable and dependent upon local conditions. Snow falls upon all the high mountain ranges.
Temperature
With the exceptions of portions of California, Arizona, and Texas the average annual surface temperature of the dry-farm territory of the United States ranges from 40 deg to 55 deg F. The average is not far from 45 deg F. This places most of the dry-farm territory in the class of cold regions, though a small area on the extreme east border may be classed as temperate, and parts of California and Arizona as warm. The range in temperature from the