Soil Report - Agriculture et Agroalimentaire Canada

Table 27. Description of wind erodibility groups (WEG)'
Dry soil Soil
WEG
Predominant
soil texture class
aggregates erodibility
>0.84mm "I"
(%I (t/ac/yr)
1 Very fine sand ; fine
sand ; sand ; dune sand
2 Loamy sand ; loamy
fine sand
3 Very fine sandy loam ; fine
sandy loam, sandy loam
4 Clay ; silty clay ; noncalcareous
clay loam and
silty clay loam with more
than 35% clay content
4L Calcareous loam and silt
loam ; calcareous clay loam
and silty clay loam with
less than 35% clay content
5 Noncalcareous loam and
silt loam with less than
20% clay content; sandy
clay loam ; sandy clay
6 Noncalcareous loam and
silt loam with more than
20% clay content; noncal
careous clay loam with less
than 35% clay content
7 Silt ; noncalcareous silty
clay loam with less than
35% clay content
'Data source, Hayes (32)
D . SOIL INTERPRETATIONS FOR
DRAINAGE
1 310
10 134
25 86
25 86
25 86
40 56
45 48
by P.S . Chisholm, P.Eng., Associate Professor, and R.S .
Irwin, P.Eng ., Professor, School of Engineering, University
of Guelph .
The removal of excess water from subsurface horizons of
the soil profile is recognized as an effective management
practice . Drainage pipes placed at a depth of a metre or less
provide an outlet for groundwater, and intercept surface
water after it passes vertically into the soil profile . Generally,
soil drainage controls hazards to agriculture caused by
saturation in the soil profile and improves the plant growth
environment. Improvements include early warming of surface
soils and more effective germination, increase in oxygen
supply to the root zone, increase in activity of soil microorganisms
and increase in capillary water supply to the root
zone during protracted dry periods (34) .
(1) Hazards to Agriculture
Four different types of hazards to agriculture are associated
with the soil-water environment . These are : (1) excess water
in the soil profile in relation to rainfall and/or ground water ;
(2) excess surface water in relation to overflow from water
courses ; (3) reduced efficiency in field operations caused by
poorly drained inclusions in otherwise well-drained fields ;
and (4) soil degradation due to compaction of saturated soil
under heavy equipment .
50
38
Of the four hazards noted, the first two are labelled "w"
and "i" in the Canada Land Inventory soil capability classification
for agriculture (23) . Individual soil series in which
the hazards "w" and "i" occur alone or in combination, in
southern Ontario, have been identified by the Ontario Soil
Survey and are summarized by Chisholm (35) .
The third type of hazard occurs in locations where part of
a field, perhaps only a fraction of a hectare, contains soil
series in which the hazards "w" and/or "i" occur . Such
inclusions present obstacles to be detoured, and impose
inefficient patterns of movement on field operations (36) .
The fourth type of hazard results when wheel loads
exceed the load bearing capacity, which is reduced when
the profile is saturated, causing compaction (37) . Compaction
is accompanied by closure of hydraulic passages related
to soil structure and biopores, and gravity drainage is
impaired.
Whereas the "w" and "i" hazards have long been recognized,
hazards due to poorly drained soil inclusions and soil
compaction are recent concerns . The latter two hazards are
subjects of current study .
It is generally accepted that removal of excess . surface
water and/or groundwater provides effective control of the
"w" and "i" hazards related to internal soil drainage, and
would also control hazards related to poorly drained soil
inclusions . Buried drains are required to remove excess
water from the soil profile, and to provide drainage outlets .
Typically, outlet drains provide only limited hydraulic
capacity and usually overflow during the infrequent flood
events . Consequently the agricultural capability of drained
lands is not considered to be equivalent to class 1 land under
the Canada Land Inventory soil capability classification.
Also it is recognized that relief of "w" and "i" hazards is not
gained by installation of an outlet drain alone ; the relief
wanted is not anticipated without installation of necessary
buried drains in property abutting to the outlet drain .
(2) Factors that Affect Drainage for Agriculture
The primary effect of agricultural drainage works is to
increase the hydraulic capacity of natural drainage systems,
both on the landscape surface and vertically downwards
through the soil profile . Increased hydraulic capacityreduces
periods of soil saturation, lowers the groundwater table and
generally enhances the soil water regime in relation to plant
growth . In a specific soil profile, the effectiveness of
agricultural drainage works is dependent upon the soil
drainage class, the ability of the soil to transmit water
vertically through the soil profile, the source of excess water
in the soil profile (groundwater vs. surface water), the
landform, and the slope .
Drainage class, landform and land slope are determined
in the field during regional soil survey . Generalized interpretations
of the ability of the soil to transmit water vertically
through the profile, and the source of excess water in the soil
profile, are based upon regional soil survey data, together
with data from laboratory analyses of soil samples .
Each of the five preceding factors was considered in
interpretation of the drainage characteristics of individual
soils identified in the Haldimand-Norfolk Region. The
results of the interpretations formed, are summarized in a
five-symbol drainage code given for each soil in Table 28 .
Each of the symbols of the drainage code is explained, in
relation to individual soils of the study area, according to the
following information.