Farm and grazing lands throughout United States are damaged by sheet erosion far beyond common belief. The accumulating result of this process of gradually working off the topsoil is seriously reduced soil productivity over many millions of acres, including our best cropping and grazing lands. Every rainfall heavy enough to cause water to flow downhill takes toll of the surface soil, the richest part of the land. Soil particles, together with humus and plant food, are picked up and transported to lower positions or swept into the streams and thence on out to sea; or else these particles are deposited in stream channels, irrigation ditches, and reservoirs where they restrict flowage and storage capacity to the great detriment of the users of water. They also increase overflows by choking channels and thus damage crops on alluvial plains. Much material is washed out over rich valley lands where it is not needed and where it may reduce productivity or even ruin the land. It often happens that only the coarser particles are left, the finer richer material being carried away in suspension.

The direct damage from sheet erosion is incalculably vast. Gullying and sliding cause much damage to fields and overgrazed and over- burned watersheds and ranges. But this spectacular type of land impairment by unrestrained water is small in comparison with the never-ending process of soil wastage by sheets of rain water flowing down unprotected slopes. The process of planing off the surface is not conspicuous in most instances, because as a rule, only a thin layer is taken off at one time thus affecting broad areas more or less equally. Attention is not attracted to the situation until the less-productive subsoil or barren bedrock begins to appear in patches. By this time it is often too late for remedial action. At this stage the surface layer that we call "the soil” is gone and the farmer or stockman must use what is left, or abandon the depleted area.

Many farmers are cultivating the subsoil and many stockmen are being forced to reduce the number of animals carried on private and public ranges because of forage depletion directly due to the removal of the more fertile surface material.

When the topsoil or humus layer is washed off, stiffer material or else rock or gravel is usually left in its place. Always the exposed material contains less humus; hence the soil, if it may be called such, is less retentive of moisture. The exposed material over a large part of the eroded lands consists of raw clay, which bakes and loses its moisture rapidly in dry weather, contains less available plant food, is more difficult to till, sheds the rains quickly and fills the streams with flood water and silt. This exposed material, with the spongelike, absorbent humus removed, often washes faster than the soil that formerly covered it. Thus erosion goes on faster as the surface covering is removed, until bedrock, or soft, rotten rock, or gravel and loose sublayer material is reached. Such loose material often guilies so rapidly and deeply that it is impracticable for the individual farmer or stockman to carry out corrective measures.

FIGURE 209.—Prior fo August, 1928, this slope in southern Utah was good grazing land. One rain swept away the surface soil from 80 per cent of the area to a depth ranging from 2 to 12 inches. All the surface soil practically was lost like a sheet stripped from the area, save where sagebrush, cedar, and pine held back islandlike patches of the topsoil. It will be a long time before grass will come back on such land, especially if grazing is permitted within the next four years

FIGURE 210.—This steep slope of one-time excellent soil has gradually lost its entire surface layer by sheet erosion. The 1928 corn crop in this eroded field was not worth harvesting, although it was an excellent corn season for the locality, west central Wisconsin. This land should either be turned over to permanent grass or restocked with timber

There is need for a national awakening to the grave dangers attending sheet erosion. Soil-saving and water-saving terraces should be built in thousands of fields; much steep land and highly erosive soil used for clean-cultivated crops should be devoted to permanent pasture or timber; overgrazed ranges should be regulated in accordance with the carrying capacity; and fire prevention on watersheds should be pushed. If a half million acres can be terraced in one year in a single State, as was done in Texas in 1927, it is evident that terracing might be extended rapidly over enormous areas now suffering from excessive washing. If costly floods can be prevented by taking sheep off overgrazed, badly eroded watersheds from which the soil- holding plants have been stripped, as has been done in the drainage basin of Manti Canyon, Utah, numerous other ranges can be saved or restored by similar restriction or regulation of grazing. Orange groves can be protected from damage by the overwash of erosional débris, following fires in the neighboring hills, by keeping the natural brush growth safe from fires, as has been done by many growers in parts of southern California. Other areas in many other parts of the country can be similarly protected and the normally stored ground- water conserved for irrigation and urban consumption.

In the near future the nation will have to deal with the erosion problem, just as Japan and other countries have been forced to deal with it. Remedies can be applied much more effectively now than later. The sooner the problem is attacked the greater will be the saving in farm and ranch land and in farm and ranch solvency.