Advancing Sustainable Agriculture in the Pacific Northwest

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PNW CONSERVATION TILLAGE HANDBOOK SERIES
Chapter l -Erosion Impacts, No.3, December-January 1986


Rill Erosion Reduces Current Crop Yields

Roger Veseth

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.

Fig. 1. Location of slope positions sampled in the study.

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

Erosion

(cubic feet)

Tiller Density

Rill area Nonrill

(heads/ft2)

Grain Yield

Rill area Nonrill area

Summit

1

0

51

51

109

109

Shoulder

6

0.7

38

57

94

108

Upper Back

8

1.1

34

54

73

113

Lower Back

10

1.9

27

51

63

117

Toeslope

6

2.3

32

58

85

113

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA (208)885-5971
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