Geology Reference
In-Depth Information
400
350
300
Plotl-1
Plotl-2
Plotl-3
250
200
Fig. 7.1 Variations of soil
losses under continuous corn
as measured by the SCS on
three replicate plots between
1932 and 1943. Annual soil
losses range from 6 to
355 t ha −1 (data source:
National Soil Erosion
Research Laboratory USLE
data repository, Purdue).
150
100
50
0
30
35
40
45
Year
1.2
Clarinda
Geneva
Gurthrie
Hays
Lacrosse
Morris
Temple
1
0.8
0.6
Fig. 7.2 Coefficient of
variation of the mean as a
function of average annual
soil loss rates measured in
USDA-ARS research stations
under different land uses/crop
rotations. Measurement
periods ranged between 10
(Morris) and 27 years (Guthrie)
(data source: National Soil
Erosion Research Laboratory
USLE data repository, Purdue).
0.4
0.2
0
0
50
100
Average annual soil loss (t/ha)
150
200
time period: at least 10 years seems reasonable,
but Wischmeier and Smith (1978) considered
20-22 years to be desirable, as measurements
should cover a full solar cycle. Very often data are
not available for such a long time period. Plot
replication cannot entirely solve this issue, as
measuring for a shorter time period may imply
that the climatic and vegetation conditions dur-
ing the measurement period are not representa-
tive of the 'true mean'. Alternatively, integrative
techniques, assessing soil redistribution rates over
longer time spans through a single measurement,
 
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