Abstract:
In many areas of the United States, soil erosion has
become a serious agricultural problem and the State of Iowa
is no exception. People attribute this to several causes
but increased production of row crops is the principal cause.
For example, Moldenhauer and Amemiya (196g) estimated that
in the deep loess soils of western Iowa, a corn-corn-soybean
rotation without erosion control can result in soil losses
as great as 42 tons per acre annually from 9% slopes 300 feet
long, or 27 tons annually from 6% slopes 400 feet long. This
means that in only 20 to 30 years six inches of the top soil
can be lost from soils that have an allowable loss of only
0.03 inch annually.
With millions of acres of land susceptible to water and
wind erosion, methods to overcome these losses are very
vital. Therefore, much research has gone into solving this
problem but much of this has been devoted to studying the
measures that affect run-off with its subsequent nutrient
and soil losses. These measures include level terracing,
contour surface planting, contour listing, and more recently,
mulch tillage methods. Unfortunately, not much has been
done to relate erosion control measures to crop yields.
It must also be strongly emphasized that complex interrelationships
among factors and interactions of factors determine
crop yields. Any yield prediction model which does
not incorporate factors other than the one being studied
is inadequate and incomplete.
Though erosion control is possible through the manipulation
of land cover, slope length, and degree of slope, the
effects of these factors on soil losses depend on other controlled
and uncontrolled factors such as management, environment,
weather, and soil properties. In most of the erosion
control studies, however, these other yield-influencing
factors were either held constant or disregarded.
