| Kind of Crop. | Kind of Soil. | Condition of Crop. | Per cent Moisture in four feet. | |||
|---|---|---|---|---|---|---|
| Total. | Hygroscopic. | Free. | Tons per acre. | |||
| Wheat | Very sandy | Poor | 2.6 | 1.9 | .7 | 56 |
| “ | Sandy loam | Good | 12.8 | 5.6 | 7.2 | 576 |
| “ | Clay | Dead | 14.1 | 10.5 | 3.6 | 288 |
| Maize | Clay adobe | Very good | 12.9 | 8.8 | 4.1 | 328 |
| “ | Sandy loam | Fair | 6.1 | 2.3 | 3.8 | 304 |
| Barley | Black adobe | Wilting | 10.7 | 8.8 | 1.9 | 152 |
| Sugar Beets | Black loam | Good | 12.4 | 5.6 | 6.8 | 544 |
| Vines | Loam | Good | 8.5 | 5.0 | 3.5 | 280 |
| “ | Sandy loam | Poor | 1.9 | 1.5 | .4 | 32 |
| Almonds | Loam | Good | 8.5 | 6.6 | 1.9 | 178 |
| “ | Same field | Suffering | 7.9 | 6.9 | 1.0 | 80 |
| Apples | Loam | Excellent | 8.3 | 5.5 | 2.8 | 224 |
| “ | Clay | Poor | 12.3 | 10.8 | 1.5 | 120 |
| Apricots | Loam | Excellent | 6.3 | 3.3 | 3.0 | 240 |
| “ | Gravelly loam | Poor | 6.9 | 5.0 | 1.9 | 152 |
| Figs | Red loam | Good | 5.2 | 3.8 | 1.4 | 112 |
| “ | Heavy loam | Wilting | 8.6 | 8.6 | 0 | 0 |
| Olives | Red loam | Good | 5.2 | 3.8 | 1.4 | 112 |
| “ | Sandy loam | Suffering | 1.9 | 1.9 | 0 | 0 |
| Peaches | Red loam | Good | 8.2 | 5.0 | 3.2 | 256 |
| “ | “ | Poor | 6.8 | 5.0 | 1.8 | 144 |
| Prunes | Gray loam | Excellent | 11.2 | 9.0 | 2.2 | 176 |
| “ | “ | Poor | 6.4 | 5.4 | 1.0 | 80 |
| Citrus fruits | Sandy loam | Good | 6.3 | 3.1 | 3.2 | 256 |
| ““ | Sandy soil | Leafless | 3.1 | 2.4 | .7 | 56 |
TABLE SHOWING DROUGHT-ENDURANCE OF
VARIOUS CROPS IN ARID REGION.
| Free water in four feet of soil. | Crops that did well in lowest amount of moisture mentioned in first column. | Crops that suffered in highest amount of moisture mentioned in first column. | |
|---|---|---|---|
| Per cent. | Tons per acre. | ||
| 0 to 1.0 | 80 | Apricots, Olives, Grapes, | Citrus, Pears, Plums, Acacia. |
| Peaches, Soy-bean. | |||
| 1.0 to 1.5 | 120 | Citrus, Figs. | Almonds, Apples. |
| 1.5 to 2. | 160 | Almonds, Plums, Saltbush. | Barley. |
| 2 to 2.5 | 176 | Prunes. | Prunes. |
| 200 | Walnuts, Eucalyptus. | ||
| 2.5 to 3 | 224 | Apples. | |
| 3 to 3.5 | 288 | Pears. | |
| 3 to 4 | 322 | Hairy Vetch. | Wheat. |
| 4 to 5 | 400 | Wheat, Maize. | |
| 5 to 6 | 480 | Sugar beets, Sorghum. | Sugar beets. |
CHAPTER XII.
THE WATER OF SOILS.—Continued.
SURFACE, HYDROSTATIC AND GROUND WATER;
PERCOLATION.
Since all the water of soils and plants is directly or indirectly derived from the rainfall (including therein snow and hail), some general points regarding this factor require first consideration. While it is not the object of this work to discuss climatology in detail, yet the times of the year and the manner in which precipitation comes, acts upon and is disposed of in the soil under different climatic conditions, must of necessity form an essential part of its subject matter.
Amount of rainfall.—The rain falling in the course of a year is usually stated in the form of “inches” (or centimeters), implying the height of the water column that would be shown at the end of the year had it all been allowed to accumulate; or, the sum of all the successive rains (including snow) observed during the year. Since this amount ranges all the way from nothing, or a mere fraction of an inch (as in portions of the Andes, and of the great African and Asian deserts) to as much as 600 inches or fifty feet (Cherapundji in eastern India), the adaptation of agricultural practice to the maintenance of the proper moisture-supply to crops is largely a local question, oftentimes of not inconsiderable difficulty. This is especially the case where torrential rains, yielding several inches of rain in a few hours, alternate with light, soaking rainfall, as is very commonly the case in the interior of continents, and more especially in the United States east of the Rocky Mountains. Westward of the same the rainfall decreases so rapidly that at or about the one-hundredth meridian (the longitude of Bismark and Pierre, Dakota, and Dodge City, Kansas) we already reach the annual average of 20 inches, which is commonly assumed to be the limit below which crops cannot safely be grown without irrigation. The “cloudbursts” occasionally occurring within these limits are usually confined to mountainous regions, and the water they pour down on the dry soil is rarely of any direct benefit to agriculture; hence they cannot be properly counted in the general estimate of the effective rainfall. A region of high rainfall (up to 100 inches and over), however, extends along the Pacific coast from northern California through western Oregon and Washington across British Columbia to Alaska, to seaward of the Sierra Nevada, Cascade, and Alaskan coast ranges.
In the country east of the Mississippi river, the average annual rainfall ranges from 30 inches in the region of the Great Lakes, and 45 to 50 inches on the north Atlantic coast, to 60 inches in Louisiana and up to eighty in southern Florida. The average of the Mississippi Valley and Atlantic coast States is usually stated at about 45 inches, which is distributed more or less evenly throughout the year, excepting usually from six to eight weeks of more scanty precipitation in the latter part of August and in September—the “Indian summer” season; so that the winter is the season of greatest total rainfall.
Natural disposition of the Rain Water.—The rainfall is naturally first disposed of in two ways, viz., a portion which is absorbed by the soil, and another which is at once shed from the surface and constitutes the “surface runoff.” The portion absorbed into the soil is subsequently disposed of either by soakage downward into the subdrainage and through springs and seepage[81] into the streams and rivers; or by evaporation. The latter again occurs in two different ways, viz., from the soil-surface itself, or through the roots and leaves of plants. The importance of each of these modes is sufficiently great to entitle each to detailed consideration.
The Surface Runoff.—This portion of the disposal of rain may range all the way from nothing to almost totality, according to the nature of the soil and the condition of its surface.[82] Sandy soils, especially when coarse, may absorb instantly even a very heavy rainfall. Heavy clay soils when dry will at first also absorb quickly quite a heavy precipitation; but as the beating of the raindrops compacts the surface, the absorption quickly slows down, so that heavy downpours of brief duration, while wetting thoroughly into a plastic mass the first two or three inches of a clay soil, may leave all beneath dry, to be very gradually moistened by the slow downward percolation against the resistance of the air in the soil; while the greater part of the later portion of the shower will drain off the surface in muddy runlets. Certain soils classed as loams, having the property of crusting readily by rain followed by sunshine ([see chapter 7, p. 111]), in heavy showers behave hardly better than strong clay soils; shedding the water until the soaked crust gives way, and is carried off in muddy streamlets. Then begins the cutting-away of the soil that, in portions of the Cotton States, as well as north of the Ohio river, has been the cause of extensive devastation of once fruitful culture lands, the site of which is now marked by “red washes” and gullies but too familiar to the eye in many regions, especially of the southern United States.