The relation of various types of vegetative cover to soil drift

A 47,000-acre demonstration project for the control of wind erosion was established by the Soil Conservation Service, U.S. Dept. of Agriculture, in 1934 in the vicinity of Dalhart, Texas. In 1936, a research station, consisting of 912 acres, was established near Dalhart to study the causes of wind erosion and to develop methods for its control. At both of these locations studies were made of the change in elevation of ground surface of certain types of land from year to year. This change in elevation was caused largely by wind action and was found to vary considerably with different types of vegetative cover. About 16,000 10-foot readings were taken on the demonstration project and several thousand other similar readings were taken at the Sand Dune Research Station. These were made during the years 1937 to 1940, inclusive, all of which were years of below normal rainfall. It was found that: 1. The amount of soil blowing from idle or abandoned lands showed a closer correlation to the precipitation that occurred during the previous years than did crop lands. 2. Milo which was harvested with a combine or header type machine suffered much less from erosion by blowing than did milo which was hand headed. 3. Certain crops, such as broomcorn, cane, and sudan, did not lose soil because of the fact that they are usually planted thickly. Crops such as hegari, milo, kafir, and corn lost a considerable amount of soil, apparently because these crops are usually planted rather far apart in order to produce a grain crop. When the spacing of sorghum crops was controlled, differences such as this were not so apparent. 4. Wheat was variable in its ability to control wind erosion, depending entirely upon the kind of stand obtained. 5. The removal of soil from rows which ran parallel to the direction of the prevailing wind was somewhat greater than from rows which were at right angles to the prevailing wind. This difference, however, was slight in comparison to the differences caused by other factors. 6. It is indicated that terraces without vegetation on their surface do not have much effect in preventing wind erosion. When the vegetation on the terrace was heavier than it was in the intervals between terraces, however, there was a definite tendency for terraces to collect most of the soil lost from the intervals between. 7. Weeds were variable in their ability to collect soil and resist erosion. The effect of Russian thistles depended on their growth, small thick stands accumulating soil during most of the blowing season, while large thistles broke away from their roots and left the ground bare. Silver leaf nightshade which is becoming a serious pest in the Dalhart vicinity was generally an exceedingly poor cover crop, often being no better than bare ground. Other weeds had a consistent tendency to accumulate soil during the blowing season. 8. Since winds of high velocity may occur in any month of the year, either removal or accumulation of soil may occur continually throughout the year. Whether a given field loses or accumulates soil, depends upon its vegetative cover at the time of each high wind.