_Prevention of Injury to Cultivated Lands from excessive Runoff._—The fundamental remedy for the injurious effects of excessive runoff from the land surface is, of course, to facilitate its absorption into the soil to the utmost extent possible, by deep tillage; or in cases where this is undesirable (as when in rainy climates excessive leaching of the land is feared), to so direct and control the surface drainage that its flow shall nowhere be so rapid as to carry with it any large amounts of earth, or to wash out the furrows. To this end its fall must be diminished by “circling,” _i. e._, plowing nearly at right angles to the slope instead of up-and-down, and on steep slopes especially also by maintaining open furrows or ditches having a gentle fall only, into which the water can shed and flow off quietly in case the furrows, left in plowing, prove insufficient to retain and shed gradually the water they cannot hold permanently. The early adoption of this simple expedient would have wholly prevented the enormous waste of fine agricultural lands referred to above. The underdraining of lands liable to washing is a costly but highly effective means of preventing denudation; and the laying of underdrains in gullies already formed, to prevent farther deepening, is among the most obvious means of arresting farther damage. The beneficial effects of underdrainage in conserving moisture will be discussed farther on. ABSORPTION AND MOVEMENTS OF WATER IN SOILS. The phenomena and laws of capillary ascent of water in soils, as discussed in the preceding chapter, serve best to demonstrate the general behavior of liquid water within different soils and their several grain-sizes; because measurably independent of the physical changes that almost unavoidably accompany the percolation of water from above downward; whether such water comes in the form of rain, or irrigation, or even when applied with the utmost precautions in the laboratory. The “beating” of rains quickly compacts the surface to a certain extent, varying with the nature of the soil, its condition of more or less perfect tilth, and the degree of violence with which the rain strikes the surface. When the latter has been compacted by a previous rain and then dried, “baking” or incrusting the surface, the latter may almost wholly shed a rain of brief duration, which, had the surface been loose, would have been wholly absorbed, materially benefiting the crop. Such surface-crusting is, therefore, injurious in preventing the absorption of water from above; and in addition, it serves to waste, by evaporation, the moisture contained in the underlying soil and subsoil. For the crust being of a finer (single-grain) texture than the tilled portion beneath, it will forcibly abstract from the latter, by absorption, its capillary moisture, and evaporating it at the upper surface, continue to deplete the land, to the great injury of crop growth, until destroyed by cultivation.[84]