Fig. 40.—Erosion in Mississippi Table Lands,
causing destruction of agricultural value
both of Uplands and Valleys.
(McGee, 12th Ann. Rept. U. S., 1890-91.)
Washing-away and Gullying in the Cotton States.—Nowhere perhaps have these effects been so severely felt as in portions of northwestern and central Mississippi, and this case is so instructive as to deserve a more detailed description. In the regions in question the soil stratum consists of a yellow or brownish loam from three to seven feet in original thickness, constituting a very desirable class of gently rolling uplands, which at one time claimed to be the best cotton-growing portion of the State. It was originally covered with an open forest of oaks, with an abundant growth of grasses that afforded excellent pasture to deer and cattle; a natural park gay with flowers during most of the season.
When these lands were taken into cultivation little or no attention was paid to the direction of the furrows and rows of corn and cotton; most commonly the plowing was done “up-hill and down,” so that the “dead-furrow” afforded a ready opportunity for the formation of washes cutting into the subsoil, during the torrential rains sometimes falling during the summers. Even when filled with soil by plowing, these washes would frequently re-open during rains, shedding the soil in a muddy flood upon the lower lands. The washing-away of the surface soil, thus brought about, of course diminished the production of the higher lands, which were then commonly “turned out” and left without cultivation or care of any kind. The crusted surface shed the rain water into the old furrows, and the latter were quickly deepened and widened into gullies—“red washes”—whose presence rendered any resumption of cultivation difficult. In the course of a few years the soil-stratum of brown loam was penetrated into the loose or loosely cemented sand which underlies it almost everywhere, and is very readily washed away. Soon the water, gaining yearly in volume, undercut the loam stratum so as to cause it to “cave” into gullies in huge masses, which with the sand were carried into the valleys adjacent, filling the beds of the streams so as to cause their flow to disappear under the flood of sand. As the evil progressed, large areas of uplands were denuded completely of their loam or culture stratum, leaving nothing but bare, arid sand, wholly useless for cultivation; while the valleys were little better, the native vegetation having been destroyed and only hardy weeds finding nourishment on the sandy surface.
Fig. 40a.—Erosion in Mississippi Table Lands, causing
destruction of agricultural value both of Uplands and Valleys.
(McGee, 12th Ann. Rept. U. S. G. S., 1890-91.)
In this manner whole sections, and in some portions of the State whole townships of the best class of uplands have been transformed into sandy wastes, hardly reclaimable by any ordinary means, and wholly changing the industrial conditions of entire counties; whose county seats even in some instances had to be changed, the old town and site having, by the same destructive agencies, literally “gone down hill.” This destruction of lands was greatly aggravated by the civil war, during which, and for some time after, large areas of lands once under cultivation were left to the mercy of the elements.
Injury in the arid regions.—In the arid regions, where the rainfall frequently comes in heavy downpours or “cloudbursts,” immense damage to pasture lands has been brought about by overstocking, in Arizona and New Mexico; involving the destruction of the natural cover of vegetation and the loosening of the surface especially by sheep; after which a heavy rainfall will carry off the surface soil, the muddy water being gathered largely in the trails made by cattle going to water. Thus gradually gullies are formed, which enlarging more and more become ravines and cut up the pasture slopes into “bad lands,” useless equally for pasture and for agriculture.[83] California, eastern Oregon and Washington, and Montana, offer striking and lamentable examples of the same destructive agencies.
Deforestation.—The deforestation of hill and mountain lands has, the world over, led to similar results; causing not only the destruction of pasture and agricultural lands, but also the conversion of streams, flowing from springs and seepage all the year, into periodic torrents, flooding the lowlands during rains by the rapid running-off of the water from the bare and hard-baked mountain slopes, and then running dry within a short time, so as not even to afford drinking water to pasturing cattle in summer. Thus for half a century the unsolved problem of the “correction of the waters of the Jura mountains” was before the Swiss and French governments; and the great and costly public work involving re-forestation, deflection of torrents and filling-in of deep ravines and gullies, is not even yet nearly completed. In Spain, which in the time of the Roman occupation was largely a forest country with abundant rainfall, the same results are seen, notably in the South, in the wide, and mostly dry, sandy beds of streams once running deep and clear; and in the scarred hill-and mountain-sides, and scant vegetation of low shrubs (“chaparral”) that replace the once abundant tree growth, e. g., in Old and New Castile. Unfortunately the lessons taught by the bitter experience of the old world seem to require actual repetition in the new, before means of prevention are even thought of.
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.