Although the percentage of surface irrigated land in
the United States is declining, it is still used on
43% of the irrigated land, and 51% of the surface
irrigated land is irrigated down furrows or rows
(USDA, 2004). Water flowing in irrigation furrows often detaches
and transports soil, reducing crop productivity and impairing
off-site water quality. Crop yields were at least 25%
less on fields eroded from over 80 years of furrow irrigation
in south-central Idaho (Carter et al., 1985). Measured soil
loss from furrow irrigated fields in this area varied from 1 to
141 Mg ha-1 annually (Berg and Carter, 1980) while the annual
average soil loss from the entire irrigated tract was 0.46 Mg
ha-1 in 1971 (Brown et al, 1974). This soil, and associated nutrients,
is transported with irrigation water as it returns to the
Snake River.
The Natural Resources Conservation Service (NRCS) and
other land planning agencies need a tool to predict furrow irrigation
erosion to assess the extent of the problem and to
compare conservation practices applied to irrigated land. An
evaluation of the Water Erosion Prediction Project (WEPP)
model indicated that it could not be used to predict furrow irrigation erosion without substantially adjusting erodibility
parameter values (Bjorneberg et al., 1999). The model also
over-predicted sediment transport capacity resulting in no
predicted sediment deposition on the lower end of fields, although
data and observations document much on-field deposition
(Bjorneberg et al., 1999).
The Idaho NRCS, in consultation with scientists and engineers
at the Northwest Irrigation and Soils Research Laboratory,
Kimberly, Idaho, developed a simple empirical model
for estimating annual irrigation-induced soil loss from furrow
irrigated fields. The SISL (surface irrigation soil loss)
model was developed in 1991 based on over 200 field-years
of data from southern Idaho. This model estimates soil loss
at the end of the furrow and does not account for deposition
or additional erosion that may occur in the drainage ditch at
the end of the field. The only published documentation of this
model is Idaho NRCS Agronomy Technical Note No. 32. Idaho
NRCS uses this model to assess benefits of conservation
practices, such as converting from furrow to sprinkler irrigation,
but this model has not been independently evaluated.
Therefore, the objective of this study was to compare the
SISL model with erosion data collected from furrow irrigated
fields near Kimberly, Idaho and Prosser, Washington
