PNW CONSERVATION
TILLAGE HANDBOOK SERIES
Chapter l -Erosion Impacts, No.3, December-January 1986
The dramatic reductions
in yield potential as a result of topsoil loss from years of soil erosion
is well known in the Northwest. However, little has been reported on the
impact of over-winter erosion on the yield of the current winter crop,
Besides reducing future yield potential, soil erosion also can have a
short-term impact on profit which should not be overlooked, particularly
with the current economic situation.
The loss of soil in small runoff-erosion channels, called rill erosion,
is a common type of over-winter soil erosion in the Northwest. The impact
of rill erosion on current winter wheat crop yield is being evaluated
in producer's fields near Pendleton, OR, by two STEEP researchers. Clyde
Douglas and Paul Rasmussen, USDA-ARS soil scientists at the Columbia Plateau
Conservation Research Center, have been involved in the study the past
2 years.
In the 1984 winter wheat crop, four field sites were studied where rills
ran parallel to the drill rows. Each site evaluated slope positions from
the summit to the toeslope (Fig. 1). Paired samples 24 x 48 inches
were taken on each slope position. One sample centered over a single rill
and the other sample was on a nonrilled area within 4 feet of the rill
sample.
Table 1 shows the impact that rill erosion had on winter wheat tiller
density and grain yield. As the rill size and soil loss increased downslope,
tiller density and grain yield decreased in the rill area. The toeslope
was an exception, possibly because of soil water accumulations from upslope
runoff, creating a more favorable environment for plant recovery. Most
of the yield reduction in the rilled area appeared to be related to a
decrease in tiller density, which in turn, was most likely related to
loss of stand in or adjacent to the rill.
The study shows that rill erosion can have a significant detrimental effect
on grain yield in the growing crop. Yield losses up to 46 percent were
measured in the rilled areas compared to nonrilled areas. Even shallow
rills appeared to cause a yield loss, apparently because of decreased
plant vigor and survival over the winter. The researchers estimated a
7 bushel per acre winter wheat yield loss where a rill occurred every
10 feet across the slope. Research on the current yield impact of rill
erosion will be repeated to compare 3 years of data.
Table 1. Impact
of over-winter rill erosion on tiller density and grain yield of winter
wheat in four field locations near Pendleton, OR, 1984(Oregon State University,
Ag. Experiment Station Special Report 738).
| Slope Position | Slope
|
Sample Area
(cubic feet) |
Rill area Nonrill
|
Rill area Nonrill area |
||
| Summit |
|
|
|
|
|
|
| Shoulder |
|
|
|
|
|
|
| Upper Back |
|
|
|
|
|
|
| Lower Back |
|
|
|
|
|
|
| Toeslope |
|
|
|
|
|
|
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