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Furrow Irrigation of a California Orchard (Photo by courtesy office of Irrigation Investigation United States Department of Agriculture) parts of this country. King has shown that the yield of these crops can be greatly increased by supplementing the rainfall with irrigation. Two examples will suffice: An average of two crops of potatoes gave an increase of 105 bushels per acre due to irrigation. In 1894 he reports a crop of flint corn yielding 14.5 tons of dry matter per acre on an irrigated plot while the same corn yielded not more than 4 tons when receiving only the natural rainfall.

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Increased yield of potatoes as a result of irrigation in humid climate (Wisconsin).

The irrigated plots represented by the two piles on the right yielded 105 bushels more per acre than the unirrigated on the left. (Drawn from half tone).

It is more than probable that the future will see irrigation in extensive use east of the Mississippi, but at the present time it is only in the expermental stage, and it has yet to be demonstrated that it will be profitable with ordinary crops under practical conditions. It is to be hoped that experiments along this line will soon be made, but they should be undertaken only by men who have made a study of the subject, for in humid climates irrigation in untrained hands may produce more harm than good.

CHAPTER VIII

SUMMER FALLOWING

Origin of Fallowing.—The practice of fallowing or “resting” the land is a very old one, being mentioned in the twenty-fifth chapter of Leviticus, where the people are commanded to rest the land every seventh year. “The seventh year shall be a sabbath of rest unto the land.” It is not known if this law was introduced into the Jewish code from a knowledge of the effect of fallowing on the soil, or if it had more to do with the mystical meaning that seems to be associated with the number seven in the Hebrew religion.

A study of the history of agriculture leads one to believe that when the nomadic tribes first settled down to anything like systematic cultivation of the soil, they grew one crop (probably of the wheat family) continuously on the same field, until the soil became so impoverished that it could no longer be tilled with profit. They then moved to other sections where virgin soil was to be found, and repeated the process. In the course of time it was discovered that these lands which had been abandoned would again produce good crops after a period of “rest” as it was called. This led to the practice of cropping the land one year, and allowing it to lie idle the next. It was later discovered that if the soil was frequently stirred during its resting period the growth the following year would be much more luxuriant than if the ground was left undisturbed. From this beginning arose the practice of summer or bare fallowing as it is understood to-day. Later experimenters found that practically as good results could be obtained by the use of the so-called "fallow crops” in place of the year of rest. These are simply crops like Indian corn, turnips, potatoes, etc., which are intertilled and kept free from weeds during at least a part of their period of growth, and their introduction has practically done away with the use of the bare fallow in most localities.

It is now well understood that what was formerly called resting the land is in reality a method of bringing about ideal conditions for the transformation of potential food into forms available to the plant. This practice of fallowing the land has practically fallen into disuse, but is being so strongly advocated in some quarters at the present time that it seems proper briefly to discuss the subject here.

Fallowing adds nothing to the Soil.—The chief advantages claimed for summer fallowing are: (1) It makes plant food available, thus increasing the succeeding crop. (2) It enables one to rid the land of weeds. (3) It destroys large numbers of injurious insects. It is doubtful, however, if under good conditions of tillage and soil management, fallowing is ever necessary. It adds nothing to the soil, but merely presents conditions that are favorable to the conversion of potential plant food into available forms; and the increase in the crop following the fallow is seldom sufficient to recompense the farmer for the year of non-production. The crude methods of culti

vation in use in earlier times doubtless made fallows necessary, but the introduction of modern machinery,

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Diagram showing the construction of the lysimeter used at the New

York State Experiment Station to study the loss of nitrogen from the soil

by leaching and more rational methods of tillage, have for the most part removed this necessity.

There is no doubt of the efficiency of fallowing as a method of making plant food available, especially if the soil is frequently stirred. The conditions brought about by this treatment of the soil are just those

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