To make an effective earth mulch the cultivation should be shallow and frequent, the aim being to make the layer as dry as possible. A rain, of course, will again compact the loose earth, and renew the capillarity, so that the cultivation should be repeated as soon as may be after a rain. Even in the absence of rain the mulch will sooner or later become compact of itself if left too

Soil which is badly in need of tillage. The cracks allow large amounts of water to be lost by evaporation

long without stirring. It is desirable to loosen the soil more frequently in the spring than is necessary later in the season. A mulch about three inches deep has been found to be most effective in conserving moisture, and it has also been shown that mulches produce relatively better results in sandy soils than in clay or loam.

Late Fall Plowing to Conserve Moisture.-Plowing the ground late in the fall tends to save the moisture, as the loose ground turned up by the plow prevents loss of water by evaporation. The broken uneven

An

surface also makes it possible for the soil to absorb more of the water from the winter rain and snow. experiment reported from Wisconsin shows that a plot plowed in the fall contained 1.15 acre inches more water than an adjacent plot not so plowed. It must be borne in mind, however, that fall plowing is not a practice

capable of universal application, for there are certain hard soils with a low humus content which may be badly puddled if fall plowed. Here, as everywhere in farming, good judgment is called for on the part of the farmer.

Early Spring Plowing to Conserve Moisture.Plowing the ground very early in the spring is a rational practice, for there is no other season when tillage is so effective in conserving the moisture of the soil. King reports one experiment where early plowed ground, seven days after plowing, contained an amount

of water equal to 1.75 inches in excess of an adjoining plot which was not plowed. Quiroga, in a thesis presented to the College of Agriculture, Ohio State University, reports that the moisture content of the early plowed plots was higher than the late plowed throughout the season. He found also that the available nitro

Weeds are objectionable because they remove large quantities of water and available plant food which are needed by the crop

gen was much higher, in the early plowed plots, and that the yield of corn was greater. All evidence indicates that the soil should be stirred as early in the spring as can be done without injury to its texture, either by plowing or by the use of some form of cultivator or harrow.

Tillage Destroys Weeds.-Lastly, tillage is useful in destroying weeds. Weeds should not be permitted to grow because they rob the crop of its moisture and plant food. During growth all plants pump up water by means of their roots, and give it off through the leaves. It has been shown that at the best the supply

of water in the ground is seldom sufficient for a maximum crop so that any withdrawal of water from the soil by the weeds works a positive injury to the desirable plants. While it is probable that the weeds do the greatest injury to the crop by depriving it of water, they also rob it of nitrogen and mineral food. Some farmers argue that if the weeds remain on the ground they are removing no fertility, but it must be remembered that they are using that portion of the plant food that could be used by the crop and that the weeds must decay before this food is again rendered available, so that so far as the present crop is concerned the food is as completely removed as it would be if taken from the field. The destruction of weeds was formerly regarded as the only reason for tillage after seeding. It is now known that stirring the soil has a distinct value in itself, and that the killing of the weeds is really secondary. In fact if the farmer so tills his farm as to reap the maximum benefits to be derived from this process he will have no need to worry about the weeds.

CHAPTER VII

DRAINAGE AND IRRIGATION

Film Moisture and Ground Water.-An important method for increasing the fertility of some classes of soils is that of underdraining by the use of tile or

other means. Water exists in the soil in two principal forms, viz: as the film or capillary moisture previously discussed, and in the form known indiscriminately as free water, ground water, or hydrostatic water. In the latter condition the water occupies the spaces between the soil grains, and is not held by the attraction of