- R.G. Kachanoski, M.H. Miller, R.D. Protz and D.A. Lobb, Department of
Land Resource Science, University of Guelph, Guelph, Ont., and E.G. Gregorich,
Agriculture Canada, Ottawa, Ont.
Evaluation Summary (Tech. Transfer Report Summaries)
View / Download Final Report [1959 KB pdf]
Associated SWEEP/LSP Research
Completed: January, 1992
soil erosion, soil loss, topography, shoulder slope, slope position,
soil management, Cesium 137
This report documents the rationale, objectives, and general methodology
of the SWEEP/TED Management of Farm Field Variability Project. In addition,
two specific aspects of that project are also documented.
In the first study the movement of soil in a complex three dimensional
landscape typical of southern Ontario is examined using 137Cs
as a soil tracer. The study made use of a previous study by L.S. Crosson
and R.D. Protz in the Department of Land Resource Science, University of
Guelph. They sampled 180 soil landscape positions in a 10 m by 10 m grid
in 1972 and stored the soil cores. The site was resampled in 1987 and through
the SWEEP/TED program the soil samples were analyzed for 137Cs.
The 137Cs in soil comes from atmospheric deposition (fall-out)
from above ground nuclear testing in early 1950's and 1960's. The 137Cs
does not naturally occur in soil, but when added to soil it binds tightly
and is not leached or taken up by plants to a significant extent. The
137Cs deposited by the atmospheric deposition was subsequently
mixed evenly in the plow layer by tillage. Thus, the movement (losses or
gains) of 137Cs in a landscape is caused by the movement of soil.
The 137Cs landscape study indicated that soil losses on shoulder
and crest slope landscape positions were greater than 100 t/ha/yr. This
confirms earlier observations by L.A. Battiston and M.H. Miller, Department
of Land Resource Science, University of Guelph, that these are areas of
severe erosion. Total field scale soil loss was negligible with concave
lower slope areas gaining all of the soil lost on the convex upper slope
areas. The major conclusion is that water erosion is not likely the major
process responsible for the soil loss. This suggests that the assumption
that crop productivity losses from erosion and the environmental effects
of erosion are linked, is not valid. Significant soil redistribution is
occurring within the complex topography of Ontario, which is not related
to the off field transport of sediment, phosphorus, and other chemicals.
In the second study summarized in this report, the processes responsible
for the severe erosion on upper slope landscape positions, specifically
shoulder slopes, are investigated. The study was carried out as part of
the M.Sc. thesis research of D.A. Lobb, Department of Land Resource Science,
University of Guelph. The hypothesis was that the soil being lost on these
slope positions is the result of the mechanical action of tillage equipment.
Tillage erosion, the net downslope translocation of soil by tillage,
was measured on eight shoulder slope landscape positions in two topographically
complex field sites typical of the upland regions of southwestern Ontario.
Cesium-137 was utilized as a labelling element to generate a tracer-pulse
for the measurement of soil translocation. Soil translocation was calculated
using the synthetic step response distribution synthesized from a succession
of convoluted 137Cs pulse response distributions. Paired plots
were utilized to compare soil translocation by upslope and downslope tillage.
A single sequence of conventional tillage operations, consisting of fall
moldboard plow, and spring tandem disc (double pass) and C-tine cultivator
(single pass), translocated upslope approximately 80 kg of soil per meter
slope width when tillage was conducted upslope, and translocated downslope
120 kg/m slope width when tillage was conducted downslope. Therefore, the
net downslope soil translocation of two tillage sequences, one upslope and
one downslope, was approximately 40 kg/m slope width. Assuming tillage operations
are conducted upslope and downslope equally as often, the rate of net downslope
soil translocation would be approximately 20 kg/m slope width per tillage
sequence. Assuming one sequence of tillage operations occurs per year, the
rate of net downslope soil translocation would be approximately 20 kg/m
slope width per year. The convex slope length between the crest and the
position of the plots was approximately 3 m. Assuming this distance was
the source length for the net downslope soil translocation, 20 kg/m slope
width per year represents the total annual soil loss from the 3 m slope
length. The average annual soil loss over this convex slope length would
be 6.7 kg/m2/yr, or 67 t/ha/yr, when tillage operations occur
upslope equally as often as downslope. Tillage erosion is a major cause
of the severe soil loss observed on shoulder slope landscape positions in
the complex topography typical of the upland regions of southwestern Ontario.
The significance of the conclusion that soil loss by tillage translocation
is an order of magnitude higher than soil loss by water cannot be overstated.
The implications are discussed in detail in this report. Briefly, soil loss
by tillage will be restricted to the upland regions of Ontario, but will
occur to some degree on all convex slope positions in all regions with complex
topography. The validity of all soil loss and erosion estimates using any
form of soil tracer such as 137Cs are questionable unless the
changes are known throughout the landscape. Predictive soil loss and crop
productivity models that do not include the process of soil loss by tillage
will not represent reality for cultivated land in complex topography and
will have little predictive value. Preventative and remedial managements
which do not control tillage soil loss will have little value in maintaining
or enhancing soil quality.
Recommendations are also discussed and include reducing the frequency
and intensities of tillage. In addition, the size of tillage implements
should be reduced. The possibility of varying tillage patterns within fields
is also discussed. Further research, on the amount of tillage soil loss
by secondary tillage implements and the amount of loss under different topographic
shapes and equipment speeds needs to be carried out.
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
The intent of the study was to examine the relationships between soil
loss, landscape configuration and slope position on Ontario croplands. Of
question to the investigators was the tenet that most soil loss on complex
landscapes in Ontario was caused by soil erosion by water and that the process
was directly linked to surface water contamination.
The study was divided into two parts:
to quantify in situ losses of soil from complex landscapes;
to examine the process of soil loss from these areas.
In the first study, Cesium 137 was used as a radioactive isotope tracer
to correlate with soil loss following calibration procedures. The field
site was first sampled on a grid pattern in 1971 for detailed soil and landscape
features. The soil material was stored and subsequently analyzed for Cesium
137 in 1986. The procedure was repeated in 1986. Changes in the surface
content of Cesium 137 were compared to the 1971 data. On the silty soils
found in the field site, marked drops in 137Cs content on crest
and shoulder slope positions were observed. Considerable increases were
observed in lower slope positions and depressional areas. Using calibration
procedures and mathematical models the rate of soil loss and gain was estimated.
The rates were up to 100 t/ha/yr from convex slope positions. This far exceeds
predictions from other models such as the Universal Soil Loss Equation (USLE).
The process of soil erosion on complex topographies with erodible materials
was examined in the second study. First, the processes of soil erosion were
explained and evaluated for the likelihood of explaining the relationships
observed in the first experiment. From the literature, this study and previous
work in Ontario, tillage erosion was identified as having a potential causal
relationship with extremely high erosion rates on complex topography. The
planing and displacement effects of tillage implements were examined. Cesium
137 was sampled before and after a variety of tillage passes on metre-wide
strips along the contours of slope positions. Upslope and downslope operations
were examined. If, on average, an operator plows up and down slope the same
number of times over any landscape position, the net loss could be up to
the equivalent of 67 t/ha/yr on shoulder slope positions.
The investigators concluded that wind and water erosion processes could
not explain soil losses of these extremes (USLE predictions would be 10
to 30 t/ha/yr). The investigators concluded that excessive tillage is directly
related to the loss of soil and its productive capacity.
A combination of research vision, understanding of geomorphological processes
and mathematical modelling make this study among the most comprehensive
and controversial studies conducted within the TAP sub-program of SWEEP.
This information could be particularly useful for the research community
as a hypotheses-generating document for further work. It could also shed
light on program planning and extension work in tillage and cropping systems
on upland soil- landscape conditions in Ontario. For programming, perhaps
water quality and soil erosion are not necessarily linked - soil quality
and productivity are also valid rationales for financial and technical assistance.
For extension work, excessive tillage is directly and not just indirectly
related to soil productivity and financial losses. Conservation tillage
and no-till may be appropriate technologies for yet another reason.
However, it should be clear that this is a well done case study. It is
difficult to extrapolate to all upland or complex topographies without a
more comprehensive process study.
- SWEEP Report #45
- Management of Farm Field Variability. III. Effect of Tillage Systems on
Soil and Phosphorus Loss
- SWEEP Report #46
- Management of Farm Field Variability. IV. Crop Yield, Tillage System,
and Soil Landform Relationships
- SWEEP Report #49A
- Land Reshaping of Lowland Clay Soils. I. Field Study
- SWEEP Report #55
- Soil Loss by Tillage Erosion: The Effects of Tillage Implement, Slope
Gradient, and Tillage Direction on Soil Translocation by Tillage
- SWEEP Report #60
- The Effect of Conservation Tillage Practices on the Losses of Phosphorus
and Herbicides in Surface and Subsurface Drainage Waters
- SWEEP Report #66
- Volume V. Economic Assessment of the Technology Evaluation and Development
Future Research: ( ) indicates reviewers suggestion for
priority, A - high, C - low.
(C) An integrated research program is needed to examine erosion and other
degradation processes and the impact of current and remedial practices on
soil quality on Ontario cropland. From this, knowledge could be gained about
the relative impact of tillage, water and wind erosion on a variety of representative
soil and landscape conditions.
(A) Further, the impact of tillage and cropping practices could be examined.
And finally, changes to farming systems as well as rehabilitative work could
be tested to determine the effectiveness of conservation measures. This
study could complete the much needed work left undone by the successful
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