The mandate of the Soil
and Water Environmental Enhancement Program (SWEEP) was to reduce
phosphorus loadings to the Lake Erie basin and to maintain or improve
agricultural productivity by reducing or correcting soil erosion and
degradation. Conservation cropping and tillage systems were identified
as the best means to achieve these goals over such a wide geographic
region as the Lake Erie watershed. The Pilot Watershed Study (PWS) was
developed as a means of evaluating the impact of conservation systems on
soil erosion and degradation, water quality and crop production when
implemented on a watershed basis.
The erodibility of soil
is a major factor which determines the extent of soil erosion occurring
on a landscape. Soil erodibility potential depends on such properties as
soil particle size distribution, organic matter content, aggregate
stability, bulk density and soil structure. The removal of topsoil by
erosion results in changes in these soil properties. The major cause of
these changes has been attributed to shifts in land management practices
or cultural practices. Prominent among the factors which change soil
quality are tillage practices, cropping systems or crop sequences,
manure and fertilizer applications and crop residue management.
Identifying the components of these systems that improve soil quality
has been the focus of numerous research undertakings.
At the watershed level in
the PWS the evaluation of conservation systems focused on changes in
soil cover. This was the one factor affected by crop production
practices that most directly influenced soil erosion control, sediment
delivery and ultimately water quality as evidenced by sediment and
phosphorus loadings. Target soil cover levels were set in order to
provide a tangible and achievable goal for the cooperators to strive
for. It was anticipated that these targets, when met, would reduce soil
loss on average by at least 50%.
In the PWS the impact of
conservation systems on crop production at the farm and field level were
left to the cooperators to evaluate in the context of their own
operations, their previous experience and their personal production
goals. Since the indicators of adoption were strong and favourable it
was concluded that during the study, cooperator evaluations of the
conservation systems were positive.
For comparative purposes,
however, information related to two crop production parameters, use of
commercial phosphorus fertilizer and crop yields, is also reported on a
Soil quality monitoring
was implemented on a series of soil benchmark sites located within the
study watersheds. Using the results of a literature search, a sampling
scheme was designed to monitor a broad range of soil properties on an
annual basis over the duration of the program. During the spring of
1990, the client directed that the soil monitoring component be expanded
to include measurements of seasonal variability in soil physical
properties. Of the 38 original soil benchmark sites, 18 were selected (3
in each of the 6 watersheds) for this additional work.
Soil cover within the
cropped areas of the watersheds was estimated using either the knotted
rope method or a series of assumptions based on previous knowledge or
experience. Factors affecting crop production were tracked on a field
basis by monitoring cooperator management decisions, weather, soil
fertility and crop pests.
The components of the
study documented in this report apply specifically to the following PWS
Establish soil, water and
crop yield baseline conditions and monitor changes in relevant
parameters throughout the life of the program;
Correlate changes in
soil, water and crop yield parameters to soil and water conservation
practices and systems.
The specific objective of
the soil quality monitoring component of the PWS was to measure changes
in selected soil parameters over the life of the project at benchmark
sites in the test watershed and to compare these with changes at
comparable sites in the control watershed. Sites were selected on the
principle soils in the watersheds on landscape positions representative
of the selected soil types.
The scope of this
To assess the effect of conservation farming
practices and systems on soil properties which are known to affect
crop productivity and/or the magnitude of soil erosion, sediment yield
To provide soils information needed for comparing
crop performance between conservation farming systems and conventional
To provide soils data from refining preliminary
estimates of soil loss using the Universal Soil Loss Equation (USLE)
and to determine the extent of any changes in the soil related values
of parameters in the USLE during the life of the project.
The literature review
suggested that improvements would be seen in those soil parameters
monitored at the soil benchmark sites managed under conservation systems
relative to those managed conventionally.
The specific objectives
of the crop monitoring program were as follows:
to determine the proportion of the soil surface
covered with live crop or dead crop residue at critical times in the
to monitor pests, soil fertility, weather, and
other factors that influence crop performance during the crop
production season; and
to monitor whole plant grain yields of crops.
In general there appeared to be more measurable and
contrasting change occurring amongst the soil quality parameters in
the three test watersheds than in the three control watersheds
although the change was not consistent amongst parameters or slope
Uncontrolled differences and/or similarities in
tillage and cropping practices between and amongst soil benchmark
pairs made it difficult to monitor significant changes in soil quality
parameters in the short term (3 years) of the PWS.
In general the amount of soil cover and area
affected increased in the test watersheds during the study and
relative to the control watersheds.
Approximately one half to three quarters of the
monitored agricultural areas within the test watersheds that were
affected by elevated soil cover levels (20%+) during spring runoff,
continued to be affected by soil cover levels greater than 20% after
planting (during late May and early June).
The adoption of conservation systems during the PWS
impacted to a greater degree on the soil cover remaining after spring
runoff when compared to the soil cover remaining after planting.
Understanding the influence of the adoption of
conservation measures on soil cover within the Pittock watersheds was
complicated by the presence of hay-based rotations.
At the beginning of the PWS the actual application
of phosphorus fertilizer on a watershed basis was approximately 1.4 to
3.6 times greater than recommended amounts and at the end of the PWS
the actual application of phosphorus fertilizer on a watershed basis
fell to approximately .8 to 1.3 times the recommended rates.
Over application of phosphorus fertilizers can be
significantly reduced on a watershed basis if information about soil
fertility levels and phosphorus loading of water courses is provided
to the producers.
No difference in crop production potential was
detected between each pair of test and control watersheds based on
yield data (or any other data) collected during the PWS.
In future projects, consideration should be given
to holding soil samples, or perhaps splitting each soil sample and
holding one of the resulting samples, through the life of the project
(or for a suitable timespan) and having all of the samples analyzed by
the same laboratory at the same time. This would avoid potential
problems with changes in laboratory and analytical techniques that may
impact on the study results.
In short term projects (less than five years) it is
critical that paired sites are similar not only in soil character but
in soil management as well. Current management practices can influence
yearly results and where long term trends are not an objective of the
study, short term soil management practices should be similar between
pairs and if possible groups of pairs.
To obtain long term trends of change the monitoring
period of soil benchmark sites should be carried out over five years
or more. This would allow for the adoption and incorporation of
conservation practices as part of the normal farming system.
The soil benchmark data collected during the PWS
could serve as a baseline data set from which future changes in soil
quality could be monitored. In the Essex and Kettle watersheds in
particular it is likely that the adoption of conservation systems will
continue in the future. It is recommended that these soil benchmark
sites be monitored every three to five years where adoption of
conservation measures has occurred and alternatively where
conventional practices have been maintained. This approach should
document the long term effects of both systems on soil quality.
The use of conservation practices should be
promoted to sustain increased levels of residue cover on a field or
Additional clarification regarding the potential
contribution of commercial fertilizer to phosphorus loadings should be
Producers should be encouraged to examine their
phosphorus fertilizer programs to ensure maximum efficiency.
The methods and equipment for calibrating
fertilizer application rates should be improved.