This report represents the results of a study of crop
residue conducted by a combined windshield/on-site survey of over 10,000
fields in southwestern Ontario in the spring of 1987. The purpose of the
survey was to provide a detailed data base for the Soil and Water Environmental
Enhancement Program (SWEEP). SWEEP is a 5-year program aimed at reducing
phosphorus loadings from cropland run-off and to improve or maintain the
productivity of agriculture in the Lake Erie Basin. The survey gathered
baseline data for percent residue cover of the soil surface for various
combinations of crops and tillage systems.
Conservation tillage practices increase residue cover
and enhance erosion control. This data, along with that collected in the
"Cropping, Tillage and Land Management Practices"
report of March, 1987 will allow estimation of relative soil loss from fields.
It will also serve as a benchmark against which the effect of implementing
soil and water management practices can be evaluated at the conclusion of
the SWEEP Agreement.
The survey was conducted by driving predetermined random
routes twice through the counties of the SWEEP study area, with stops approximately
every 0.8 km to record cropland information. At each site information was
gathered on present crop, residue levels of the previous crop, and tillage
An attempt was made to include a representative subsample
of interview survey sites visited in the "Cropping,
Tillage and Land Management Practices" study (Coleman & Roberts, March
1987), in order to allow comparison of crop residue data with detailed cropping
and tillage information.
An analysis of the data reveals that 16% of fields in
southwestern Ontario have 20% or more residue cover, while just 10% of the
fields surveyed had 30% residue cover.
Residue levels were compiled on a county and regional
municipality basis, by tillage type, previous crops, and cropping sequence.
Study results showed that conventional tillage occurred
most commonly (72.8%), while 18.6% of fields were not tilled, 8.0% were
reduced tilled and 0.5% were ridge tilled. Over 95% of conventionally tilled
fields occurred in the 0-15% residue category, while 3% of conventionally
tilled fields occurred in the 75-100% category. For reduced tillage, most
fields were in the 15-30% residue category at 40.6%, with a similar response
(40.0%) in the 30-45% residue category.
The higher residue categories are dominated by fields
in the not-tilled category. Most of this category was made up of forage
and hay residue. These are densely growing crops which tend to provide a
high degree of surface cover.
County results showing the distribution of crops planted
indicate that corn (26.3%) was predominant. Hay or forage constituted 20.9%,
while spring and fall grain made up 11.9% and 12.5% respectively.
To assess the representativeness of the results, the
information was compared to the distribution of crops by county found in
the report by Coleman and Roberts, 1987. A good
deal of similarity was seen among percentage occurrence of the various crops
between the two surveys.
Reliability of the crop residue estimate was judged by
a cross-tabulation of actual measured residue cover in percent with estimated
residue cover. For all residue cover categories, it was found that one can
be over 96% confident that when a residue cover class was estimated, the
value was in its proper class.
Residue levels of previous crops that were not identifiable
(fallow), occurred 3.8% of the time in the Before Secondary Tillage (BST)
phase, but their occurrence increased to 12% in the After Secondary Tillage
(AST) phase of the study. Results showed that during the AST phase, higher
proportions of fields occurred in the 0-15% residue cover category, while
most decreases occurred in the 45-75% and 75-100% residue categories.
With the exception of small grains, the proportion of
fields in the 0-15% residue category increased markedly during the AST phase,
for most crops.
For example, the proportion of fields in corn having
just 0-15% residue cover increased from 70.4% during the BST phase to 83.3%
during the AST phase. By comparison, the number of corn fields having residue
in the higher residue categories fell by approximately 13 percentage points.
The proportion of fields in beans having 0-15% residue
increased from 61.4% during the BST phase to 95.6% during the AST phase.
For beans, the higher residue categories lost a total of approximately 34
percentage points. With the exception of forages, corresponding losses in
residue occurred for the remaining crops.
During the BST phase, 54% of forage fields occurred in
the 0 - 15% residue category. These were fields which had been plowed down
in preparation for planting another crop. Hay which remained during the
AST portion of the study was being kept an additional year. As a consequence,
83.5% of the entries in the 75-100% residue category are a result of forages
being maintained from year to year.
Cropping sequences were one of the more interesting pieces
of information available from the survey. For example, where the present
crop was corn, 63.4% of those fields had previously been corn, 16.6% of
present corn crops had previously been small grains while 11.1% of fields
had previously been seeded to beans. Four percent of present corn fields
had insufficient residue to determine what the previous crop had been.
An analysis of crop residue for a previous crop-present
crop combination can show the probability of having a certain level of residue
through many types of cropping sequences. As an illustration, the mean value
of residue cover resulting from a corn-corn-grain-hay-hay rotation is provided.
In the first year when corn follows a previous crop of hay, a 10% level
of residue was found on average. In the second year when corn follows corn,
one would expect to find 12% residue cover. In the third year of the rotation,
when spring grain follows corn, an average residue cover of 9% would likely
be found. When hay follows spring grain in the fourth year, a crop residue
cover of 33% would be anticipated. In the final year of the rotation when
hay follows hay an average residue cover of 73% would result. Over this
rotation, the average value of crop residue was 27%.
Average residue cover levels for any other crop sequence
can be derived with the data found in this report. Results showed that incorporating
a forage/hay into a rotation increased crop residue cover substantially.
The survey was designed to collect information about
crop residues before secondary tillage (after-wintering) and after secondary
tillage (after-planting). The before secondary tillage information proved
to be useful only in a limited fashion. The only crops in the before secondary
tillage category during the spring are untilled crop stubble and primary
tilled fields. Forage/hay and fall planted grains are crops which have already
received secondary tillage. The main value of the before secondary tillage
portion of the survey is to allow estimation of the over-winter protection
afforded by stubble, forage or fall grain.
This data will enable additional analysis and comparisons
to be made and will be used to evaluate the effects of conservation practices
in the SWEEP program.
(From Technology Transfer Report Summaries - A. Hayes,
L. Cruickshank, Co-Chairs)