Agronomy and Horticulture Department

 

Date of this Version

1935

Comments

Published in BULLETIN 11, (1935), 1-35

Abstract

Soil erosion resulting from runoff water has come to be recognized as a national menace. The determination and evaluation of all factors influencing runoff and erosion are studies of fundamental importance, especially insofar as they may be made to yield information upon methods of control over this insidious tendency of washing away the land.

"Fully 75 per cent of the crop-producing and grazing areas of the United States is sloping enough to set in motion, moderately or violently, these wasteful processes of accelerated soil-removal and excessive runoff. That 35 million acres of formerly cultivated land have been essentially ruined by erosion and that an additional area of about 125 million acres, still largely in cultivation, have lost all or most of the topsoil, with another 100 million acres of crop-land heading in this direction, should be sufficient evidence that the problem is one of profound economic importance. Especially must this be considered true since the wastage is now proceeding faster than ever, owing to the fact that considerable time was required to strip off the more absorptive surface-layer from millions of acres, and to the further fact that the subsoil is generally more erosive than the soil. The cost runs into hundreds of millions of dollars annually, in the way of direct depreciation and essential destruction of fields and pastures, the silting of reservoirs, stream-channels and ditches, damage to highway and railway fills and embankments, choking of culverts, covering of valuable valley-lands with relatively unproductive erosional debris, and pollution of former clear-water streams with excessive loads of silt and clay washed out of the hills" (Bennett, '34).

Much experimentation has been carried on and numerous papers have been written on the effects of a forest cover in promoting absorption of rainfall and controlling erosion. But a study of grass as a stabilizer of lands and a means of increasing absorption and diminishing runoff has just begun. It has resulted from the present physical crisis in land use within the United States and especially in the west. This crisis is a consequence of the period of exploitation resulting from the rapid occupation of the whole country by a civilized people. The story of American agriculture has been one of breaking new soil, farming it hard, and then, when yields began to fall off, moving west to repeat the cycle. The time has gone, however, when worn out lands can be abandoned for virgin soils, with their stored fertility, and undepleted ranges lying to the west. These changes have occurred rapidly. As stated by Lowdermilk ('35a ): "Soils which had been thoroughly protected through thousands of years of time by unbroken mantles of vegetation, and, for this reason, had weathered to fine textures with high organic contents so favorable to 'mellowness' and good fertility, were suddenly exposed to the dash of torrential rains characterizing the climate of extensive regions. . .. Topsoils have been literally washed away, leaving raw, comparatively unproductive, unabsorptive, intractible subsoil exposed at the surface ..... of the greater part of the crop and grazing areas of the West."

The natural cover of prairie vegetation has nearly all been removed by breaking, or sorely depleted by continued overgrazing. This effective preventive of erosion has been replaced by poorly sodded pastures and lands covered only temporarily with crops. Overgrazing on the one hand and cultural practices on the other have exposed much of the surface of both to the destructive action of rain and runoff waters.

With a widespread erosion control campaign going on throughout the United States with the object of the best type of soil conservation, it is peculiarly desirable to take full account of the influence of plant cover. Moreover, in examining the effects of disturbances wrought by man, his implements and machines, and his domestic animals, it is desirable to begin investigations with undisturbed natural condition of the land. Fortunately many limited areas of natural grassland, especially prairies kept for the production of hay, remain to facilitate such comparative studies.