=163. Porosity in Relation to Water Movement.=—The intimate relation which water movement in a soil bears to fertility makes highly important the analytical study of this feature of porosity. A soil deficient in plant food, in so far as chemical analysis is concerned, will produce far better crops when the flow of moisture is favorable than a highly fertile soil in which the water may be in deficiency or excess. Aside from the actual rain-fall the texture of the soil, in other words its porosity, is the most important factor in determining the proper supply of moisture to the rootlets of plants. Even where the rain-fall is little, a properly porous soil in contact with a moist subsoil will furnish the moisture necessary to plant growth. This fact is well illustrated by the beet fields in Chino Valley, California. In this locality most excellent crops of sugar beets are produced without irrigation and almost without rain. =164. Methods of Water Movement=—The translocation of soil water is occasioned in at least two ways; namely, 1. By changing the porosity of a given stratum of soil. 2. By changing the amount of water a given stratum contains. The following experiment by King[113] illustrates a convenient method of studying this movement of water: On a rich fallow ground of light clay soil, underlaid at a depth of eighteen inches by a medium-grained sand, water, to the amount of two pounds per square foot on an area of eight by eight feet, was slowly added with a sprinkler, samples of soil having been previously taken in six-inch sections down to a depth of three feet. The samples were taken along a diagonal of the square under experiment and one foot apart. The middle sample of the line being from the center of the area. The sampling and wetting occurred between one and three P. M., on July 22, and on the evening of the 23 a corresponding series of samples was taken along a line parallel to the first but eight inches distant. The changes in the percentages of water in the soil are given in the following table, showing the translocation of water in soil due to wetting the surface: PER CENT OF WATER. DIFFERENCE. Inches. Before After In per cent. In pounds per wetting. wetting. cu. ft. 0–6 14.00 22.23 +8.23 +2.873 6–12 15.14 15.71 +0.57 +0.199 12–18 16.23 15.75 –0.48 –0.213 18–24 17.70 16.92 –0.78 –0.347 24–30 16.76 14.41 –2.35 –1.032 30–36 15.51 15.21 –0.30 –0.132