cause the drains to run. It will thus be seen that it is simply the excess of water which is removed by underdraining, and not that part which is of most importance to the plant. Although the crop probably makes little direct use of the free water, one must not lose sight of the fact that it may be drawn into the upper layers of the soil by capillarity to replace that lost by evapora

tion, and for this reason the underdraining should not be so deep as to interfere seriously with capillary action.

Drainage Sometimes Beneficial on High Lands.Strangely enough, experience has shown that it is not merely low lying soils which are benefited by underdraining. In many cases heavy clay soils in elevated positions, especially if underlaid by rather impervious subsoils, are greatly improved in tilth by tiling. In such soils the percolation is so slow that practically the same effect is produced as would be expected if the general level of the ground water were near the surface. These soils are made more mellow by drain

age and respond more readily to early tillage. Clay soils are often puddled by the fine particles in the soilwater being deposited in the spaces between the soilgrains, thus cementing them together. The use of tile will often prevent this by causing the water to sink more rapidly through the soil. Tile-drained fields are not so likely to be injured by hauling heavy loads over them as are those not so treated.

Irrigation in Humid Climates in Experimental Stage. There are large areas in the western part of this country which, for lack of sufficient water, produce very scanty vegetation, although in many instances the soil is well supplied with the other materials essential to the plant. The results to be derived from irrigation on such soils is too well known to call for comment here. The work of investigators, notably that of King, in the so-called humid climates east of the Mississippi has shown that even here the total rainfall is seldom sufficient for a maximum yield of the staple crops, and the precipitation is distributed so unevenly throughout the season that a comparatively small part of it can be used by the plants.

Many market gardeners recognize the fact that some system of irrigation is necessary for the most profitable returns, and are in the habit of supplying water artificially to their more valuable crops. Marshall P. Wilder when asked to name the three things most essential to successful strawberry culture is said to have replied: "First, plenty of water; second, more water; third, still more water."

At the present time irrigation of the staple farm crops is not practiced to any large extent in the humid.

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.

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