CHAPTER IV
DRY-FARM AREAS.--GENERAL CLIMATIC FEATURES


THE dry-farm territory of the United States stretchesfrom the Pacific seaboard to the 96th parallel of longitude, and from the Canadianto the Mexican boundary, making a total area of nearly 1,800,000 square miles. Thisimmense territory is far from being a vast level plain. On the extreme east is theGreat Plains region of the Mississippi Valley which is a comparatively uniform countryof rolling hills, but no mountains. At a point about one third of the whole distancewestward the whole land is lifted skyward by the Rocky Mountains, which cross thecountry from south to northwest. Here are innumerable peaks, canons, high table-lands,roaring torrents, and quiet mountain valleys. West of the Rockies is the great depressionknown as the Great Basin, which has no outlet to the ocean. It is essentially a giganticlevel lake floor traversed in many directions by mountain ranges that are offshootsfrom the backbone of the Rockies. South of the Great Basin are the high plateaus,into which many great chasms are cut, the best known and largest of which is thegreat Canon of the Colorado. North and east of the Great Basin is the Columbia RiverBasin characterized by basaltic rolling plains and broken mountain country. To thewest, the floor of the Great Basin is lifted up into the region of eternal snow bythe Sierra Nevada Mountains, which north of Nevada are known as the Cascades. Onthe west, the Sierra Nevadas slope gently, through intervening valleys and minormountain ranges, into the Pacific Ocean. It would be difficult to imagine a morediversified topography than is possessed by the dry-farm territory of the UnitedStates.

Uniform climatic conditions are not to be expectedover such a broken country. The chief determining factors of climate--latitude, relativedistribution of land and water, elevation, prevailing winds-- swing between suchlarge extremes that of necessity the climatic conditions of different sections arewidely divergent. Dry-farming is so intimately related to climate that the typicalclimatic variations must be pointed out.

The total annual precipitation is directly influencedby the land topography, especially by the great mountain ranges. On the east of theRocky Mountains is the sub-humid district, which receives from 20 to 30 inches ofrainfall annually; over the Rockies themselves, semiarid conditions prevail; in theGreat 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 precipitationis the chief factor in determining the success of dry-farming. However, the distributionof the rainfall throughout the year is also of great importance, and should be knownby the farmer. A small rainfall, coming at the most desirable season, will have greatercrop-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 wintermust be considerably different from those used where the bulk of the precipitationcomes 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 heintends to dry-farm before he can safely choose his cultural methods.

With reference to the monthly distribution ofthe precipitation over the dry-farm territory of the United States, Henry of theUnited 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 isfound in all of the territory west of the Cascade and Sierra Nevada ranges, and alsoobtains in a fringe of country to the eastward of the mountain summits. The distinguishingcharacteristic 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 Oregonand Washington. About half of the yearly precipitation comes in the months of December,January, and February, the remaining half being distributed throughout the sevenmonths --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 similarto 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 theapproach 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, prevailsover Arizona, New Mexico, and a small portion of eastern Utah and Nevada. This typediffers from all others in the fact that about 35 per cent of the rain falls in Julyand August. May and June are generally the months of least rainfall."

"The Northern Rocky Mountain and EasternFoothills 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; inMontana, in May and June."

"The Plains Type.--This type embracesthe 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 characterizedby a scant winter precipitation over the northern states and moderately heavy rainsduring the growing season. The. bulk of the rains comes in May, June, and July."

This classification emphasizes the great variationin distribution of rainfall over the dry-farm territory of the country. West of theRocky Mountains the precipitation comes chiefly in winter and spring, leaving thesummers rainless; while east of the Rockies, the winters are somewhat rainless andthe precipitation comes chiefly in spring and summer. The Arizona type stands midwaybetween these types. This variation in the distribution of the rainfall requiresthat different methods be employed in storing and conserving the rainfall for cropproduction. The adaptation of cultural methods to the seasonal distribution of rainfallwill be discussed hereafter.


Snowfall

Closely related to the distribution of the rainfalland the average annual temperature is the snowfall. Wherever a relatively large winterprecipitation 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 lowerand 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 andthe 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 districtswhere the average annual temperature is high. The heaviest snowfall is in the intermountaindistrict, 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 uponlocal 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 territoryof the United States ranges from 40° to 55° F. The average is not far from45° 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 partsof California and Arizona as warm. The range in temperature from the highest in summerto the lowest in winter is considerable, but not widely different from other similarparts of the United States. The range is greatest in the interior mountainous districts,and lowest along the seacoast. The daily range of the highest and lowest temperaturesfor any one day is generally higher over dry-farm sections than over humid districts.In the Plateau regions of the semiarid country the average daily variation is from30 to 35° F., while east of the Mississippi it is only about 20° F. Thisgreater daily range is chiefly due to the clear skies and scant vegetation whichfacilitate excessive warming by day and cooling by night.

The important temperature question for the dry-farmeris whether the growing season is sufficiently warm and long to permit the maturingof crops. There are few places, even at high altitudes in the region considered,where the summer temperature is so low as to retard the growth of plants. Likewise,the first and last killing frosts are ordinarily so far apart as to allow an amplegrowing season. It must be remembered that frosts are governed very largely by localtopographic features, and must be known from a local point of view. It is a generallaw that frosts are more likely to occur in valleys than on hillsides, owing to thedownward drainage of the cooled air. Further, the danger of frost increases withthe altitude. In general, the last killing frost in spring over the dry-farm territoryvaries from March 15 to May 29, and the first killing frost in autumn from September15 to November 15. These limits permit of the maturing of all ordinary farm crops,especially the grain crops.


Relative humidity

At a definite temperature, the atmosphere canhold only a certain amount of water vapor. When the air can hold no more, it is saidto be saturated. When it is not saturated, the amount of water vapor actually heldby the air is expressed in percentages of the quantity required for saturation. Arelative humidity of 100 per cent means that the air is saturated; of 50 per cent,that it is only one half saturated. The drier the air is, the more rapidly does thewater evaporate into it. To the dry-farmer, therefore, the relative humidity or degreeof dryness of the air is of very great importance. According to Professor Henry,the chief characteristics of the geographic distribution of relative humidity inthe United States are as follows:--

(1) Along the coasts there is a belt of highhumidity at all seasons, the percentage of saturation ranging from 75 to 80 per cent.

(2) Inland, from about the 70th meridian eastwardto the Atlantic coast, the amount varies between 70 and 75 per cent.

(3) The dry region is in the Southwest, wherethe average annual value is not over 50 per cent. In this region are included Arizona,New Mexico, western Colorado, and the greater portion of both Utah and Nevada. Theamount of annual relative humidity in the remaining portion of the elevated district,between the 100th meridian on the east to the Sierra Nevada and the Cascades on thewest, varies between 55 and 65 per cent. In July, August, and September, the meanvalues in the Southwest sink as low as 20 to 30 per cent, while along the Pacificcoast districts they continue about 80 per cent the year round. In the Atlantic coastdistricts, and generally east from the Mississippi River, the variation from monthto month is not great. April is probably the driest month of the year.

The air of the dry-farm territory, therefore,on the whole, contains considerably less than two thirds the amount of moisture carriedby the air of the humid states. This means that evaporation from plant leaves andsoil surfaces will go on more rapidly in semiarid than in humid regions. Againstthis danger, which cannot he controlled, the dry-farmer must take special precautions.


Sunshine

The amount of sunshine in a dry-farm sectionis also of importance. Direct sunshine promotes plant growth, but at the same timeit accelerates the evaporation of water from the soil. The whole dry-farm territoryreceives more sunshine than do the humid sections. In fact, the amount of sunshinemay roughly be said to increase as the annual rainfall decreases. Over the largerpart of the arid and semiarid sections the sun shines over 70 per cent of the time.


Winds

The winds of any locality, owing to their moisture-dissipating power play an important part in the success of dry-farming. A persistentwind will offset much of the benefit of a heavy rainfall and careful cultivation.While great general laws have been formulated regarding the movements of the atmosphere,they are of minor value in judging the effect of wind on any farming district. Localobservations, however, may enable the farmer to estimate the probable effect of thewinds and thus to formulate proper cultural means of protection. In general, thoseliving in a district are able to describe it without special observations as windyor quiet. In the dry-farm territory of the United States the one great region ofrelatively high and persistent winds is the Great Plains region east of the RockyMountains. Dry-farmers in that section will of necessity be obliged to adopt culturalmethods that will prevent the excessive evaporation naturally induced by the unhinderedwind, and the possible blowing of well-tilled fallow land.


Summary

The dry-farm territory is characterized by alow rainfall, averaging between 10 and 20 inches, the distribution of which fallsinto two distinct types: a heavy winter and spring with a light summer precipitation,and a heavy spring and summer with a light winter precipitation. Snow falls overmost of the territory, but does not lie long outside of the mountain states. Thewhole dry-farm territory may be classed as temperate to cold; relatively high andpersistent winds blow only over the Great Plains, though local conditions cause strongregular winds in many other places; the air is dry and the sunshine is very abundant.In brief, little water falls upon the dry-farm territory, and the climatic factorsare of a nature to cause rapid evaporation.

In view of this knowledge, it is not surprisingthat thousands of farmers, employing, often carelessly agricultural methods developedin humid sections, have found only hardships and poverty on the present dry-farmempire of the United States.


Drouth

Drouth is said to be the arch enemy of the dry-farmer,but few agree upon its meaning. For the purposes of this volume, drouth may be definedas a condition under which crops fail to mature because of an insufficient supplyof water. Providence has generally been charged with causing drouths, but under theabove definition, man is usually the cause. Occasionally, relatively dry years occur,but they are seldom dry enough to cause crop failures if proper methods of farminghave been practiced. There are four chief causes of drouth: (1) Improper or carelesspreparation of the soil; (2) failure to store the natural precipitation in the soil;(3) failure to apply proper cultural methods for keeping the moisture in the soiluntil needed by plants, and (4) sowing too much seed for the available soil-moisture.

Crop failures due to untimely frosts, blizzards,cyclones, tornadoes, or hail may perhaps be charged to Providence, but the dry-farmermust accept the responsibility for any crop injury resulting from drouth. A fairlyaccurate knowledge of the climatic conditions of the district, a good understandingof the principles of agriculture without irrigation under a low rainfall, and a vigorousapplication of these principles as adapted to the local climatic conditions willmake dry-farm failures a rarity.