DRY-FARMING, as at present understood, is theprofitable production of useful crops, without irrigation, on lands that receiveannually a rainfall of 20 inches or less. In districts of torrential rains, highwinds, unfavorable distribution of the rainfall, or other water-dissipating factors,the term "dry-farming" is also properly applied to farming without irrigationunder an annual precipitation of 25 or even 30 inches. There is no sharp demarcationbetween dry- and humid-farming.
When the annual precipitation is under 20 inches,the methods of dry-farming are usually indispensable. When it is over 30 inches,the methods of humid-farming are employed; in places where the annual precipitationis between 20 and 30 inches, the methods to be used depend chiefly on local conditionsaffecting the conservation of soil moisture. Dry-farming, however, always impliesfarming under a comparatively small annual rainfall.
The term "dry-farming" is, of course,a misnomer. In reality it is farming under drier conditions than those prevailingin the countries in which scientific agriculture originated. Many suggestions fora better name have been made. "Scientific agriculture" has-been proposed,but all agriculture should be scientific, and agriculture without irrigation in anarid country has no right to lay sole claim to so general a title. "Dry-landagriculture," which has also been suggested, is no improvement over "dry-farming,"as it is longer and also carries with it the idea of dryness. Instead of the name"dry-farming" it would, perhaps, be better to use the names, "arid-farming.""semiarid-farming," "humid-farming," and "irrigation-farming,"according to the climatic conditions prevailing in various parts of the world. However,at the present time the name "dry-farming" is in such general use thatit would seem unwise to suggest any change. It should be used with the distinct understandingthat as far as the word "dry" is concerned it is a misnomer. When the twowords are hyphenated, however, a compound technical term--"dry-farming"--issecured which has a meaning of its own, such as we have just defined it to be; and"dry-farming," therefore, becomes an addition to the lexicon.
Dry- versus humid-farming
Dry-farming, as a distinct branch of agriculture,has for its purpose the reclamation, for the use of man, of the vast unirrigable"desert" or "semi-desert" areas of the world, which until recentlywere considered hopelessly barren. The great underlying principles of agricultureare the same the world over, yet the emphasis to be placed on the different agriculturaltheories and practices must be shifted in accordance with regional conditions. Theagricultural problem of first importance in humid regions is the maintenance of soilfertility; and since modern agriculture was developed almost wholly under humid conditions,the system of scientific agriculture has for its central idea the maintenance ofsoil fertility. In arid regions, on the other hand, the conservation of the naturalwater precipitation for crop production is the important problem; and a new systemof agriculture must therefore be constructed, on the basis of the old principles,but with the conservation of the natural precipitation as the central idea. The systemof dry-farming must marshal and organize all the established facts of science forthe better utilization, in plant growth, of a limited rainfall. The excellent teachingsof humid agriculture respecting the maintenance of soil fertility will be of highvalue in the development of dry-farming, and the firm establishment of right methodsof conserving and using the natural precipitation will undoubtedly have a beneficialeffect upon the practice of humid agriculture.
The problems of dry-farming
The dry-farmer, at the outset, should know withcomparative accuracy the annual rainfall over the area that he intends to cultivate.He must also have a good acquaintance with the nature of the soil, not only as regardsits plant-food content, but as to its power to receive and retain the water fromrain and snow. In fact, a knowledge of the soil is indispensable in successful dry-farming.Only by such knowledge of the rainfall and the soil is he able to adapt the principlesoutlined in this volume to his special needs.
Since, under dry-farm conditions, water is thelimiting factor of production, the primary problem of dry-farming is the most effectivestorage in the soil of the natural precipitation. Only the water, safely stored inthe soil within reach of the roots, can be used in crop production. Of nearly equalimportance is the problem of keeping the water in the soil until it is needed byplants. During the growing season, water may be lost from the soil by downward drainageor by evaporation from the surface. It becomes necessary, therefore, to determineunder what conditions the natural precipitation stored in the soil moves downwardand by what means surface evaporation may be prevented or regulated. The soil-water,of real use to plants, is that taken up by the roots and finally evaporated fromthe leaves. A large part of the water stored in the soil is thus used. The methodswhereby this direct draft of plants on the soil-moisture may be regulated are, naturally,of the utmost importance to the dry-farmer, and they constitute another vital problemof the science of dry-farming.
The relation of crops to the prevailing conditionsof arid lands offers another group of important dry-farm problems. Some plants usemuch less water than others. Some attain maturity quickly, and in that way becomedesirable for dry-farming. Still other crops, grown under humid conditions, may easilybe adapted to dry-farming conditions, if the correct methods are employed, and ina few seasons may be made valuable dry-farm crops. The individual characteristicsof each crop should be known as they relate themselves to a low rainfall and aridsoils.
After a crop has been chosen, skill and knowledgeare needed in the proper seeding, tillage, and harvesting of the crop. Failures frequentlyresult from the want of adapting the crop treatment to arid conditions.
After the crop has been gathered and stored,its proper use is another problem for the dry-farmer. The composition of dry-farmcrops is different from that of crops grown with an abundance of water. Usually,dry-farm crops are much more nutritious and therefore should command a higher pricein the markets, or should be fed to stock in corresponding proportions and combinations.
The fundamental problems of dry-farming are,then, the storage in the soil of a small annual rainfall; the retention in the soilof the moisture until it is needed by plants; the prevention of the direct evaporationof soil-moisture during; the growing season; the regulation of the amount of waterdrawn from the soil by plants; the choice of crops suitable for growth under aridconditions; the application of suitable crop treatments, and the disposal of dry-farmproducts, based upon the superior composition of plants grown with small amountsof water. Around these fundamental problems cluster a host of minor, though alsoimportant, problems. When the methods of dry-farming are understood and practiced,the practice is always successful; but it requires more intelligence, more implicitobedience to nature's laws, and greater vigilance, than farming in countries of abundantrainfall.
The chapters that follow will deal almost whollywith the problems above outlined as they present themselves in the construction ofa rational system of farming without irrigation in countries of limited rainfall.