Soil capability for agriculture in Ontario

Purpose

This technical information is for municipalities, contractors and land use planners in Ontario.

The purpose of this information is to provide a comprehensive classification framework for the application of the Canada Land Inventory (CLI) Soil Capability for Agriculture to mineral soils and landscapes in Ontario. The guidelines given here supersede those provided in CLI, Soil Capability Classification for Agriculture^{footnote 1[1]}.

Introduction

The CLI for agriculture is an interpretative system for assessing the effects of climate and soil characteristics on the limitations of land for growing common field crops. Common field crops in Ontario include:

• corn
• soybeans
• small grains
• perennial forages

This system does not classify land for horticultural or other specialty type crops.

The system evaluates mineral soils’:

• productivity relative to all mineral soils in Ontario and Canada
• flexibility or range of common field crops they can produce
• management needs with respect to necessary improvements and conservation practices for field crop production

The system emphasizes the potential capability of soils. Therefore, the present land use and management of a given land area may or may not reflect its potential soil capability. For example, a forested area may rate highly under the CLI even though it has not been cleared and developed for agricultural use.

Assumptions

CLI classification depends on combinations of climate and soil characteristics which affect limitations to soil use and productive capacity for common field crops. The need for land improvement by the removal of shrubs, trees and stumps is not considered a limitation to agricultural capability unless it is considered unfeasible to remove them.

Contemporary best management practices for soil management and field crop production are in place.

The various soils within a given capability class are considered similar in degree of limitation, notwithstanding the various kinds of limitations which may be present.

The soil capability class represents the potential capability of land in its improved state. Land requiring improvements, such as stone removal or tile drainage that are feasible and can be done by the individual farmer or landowner, is classified according to what its ongoing limitations would be with the needed improvements in place. It is recognized that in some local or site-specific situations certain improvements may not be feasible even though such improvements are generally feasible on similar soils elsewhere.

The capability classification of the soils in an area may be changed when major reclamation works are installed which permanently reduce or eliminate the present limitations.

Distance to market, kind of roads, location, size of farms, characteristics of land ownership and cultural patterns and the skill or resources of individual operators are not criteria for CLI classification.

Capability groupings may be subject to change as new information about the behaviour and responses of soils become available.

Capability class and subclass definitions

In the CLI system, there are 7 capability classes. Soils descend in quality from Class 1, which is highest, to Class 7 soils, which have no agricultural capability for the common field crops. Class 1 soils have no significant limitations. Class 2 through 7 soils have one or more significant limitations, each of which are denoted by a capability subclass.

Definitions of the capability classes

Class 1

Soils in Class 1 have no significant limitations in use for crops. They are level to nearly level, deep, well to imperfectly drained and have good nutrient and water holding capacity. They can be managed and cropped without difficulty. Under good management they are moderately high to high in productivity for the full range of common field crops.

Class 2

Soils in Class 2 have moderate limitations that reduce the choice of crops or require moderate conservation practices. These soils are deep but may not hold moisture and nutrients as well as Class 1 soils. The limitations are moderate, and the soils can be managed and cropped with little difficulty. Under good management they are moderately high to high in productivity for a wide range of common field crops.

Class 3

Soils in Class 3 have moderately severe limitations that reduce the choice of crops or require moderate conservation practices. The limitations are more severe than for Class 2 soils. They affect one or more of the following practices:

• timing and ease of tillage
• planting and harvesting
• choice of crops
• methods of conservation

Under good management these soils are fair to moderately high in productivity for a wide range of common field crops.

Class 4

Soils in Class 4 have severe limitations that restrict the choice of crops, or require special conservation practices and very careful management, or both. The severe limitations seriously affect one or more of the following practices:

• timing and ease of tillage
• planting and harvesting
• choice of crops
• methods of conservation

These soils are low to medium in productivity for a narrow to wide range of common field crops but may have higher productivity for a specially adapted crop.

Class 5

Soils in Class 5 have very severe limitations that restrict their capability to producing perennial forage crops, and improvement practices are feasible. The limitations are so severe that the soils are not capable of use for sustained production of annual field crops. The soils are capable of producing native or tame species of perennial forage plants and may be improved through the use of farm machinery. Feasible improvement practices may include:

• clearing of bush
• cultivation
• seeding
• fertilizing
• water control

Class 6

Soils in Class 6 are unsuited for cultivation but are capable of use for unimproved permanent pasture. These soils may provide some sustained grazing for farm animals, but the limitations are so severe that improvement through the use of farm machinery is impractical. The terrain may be unsuitable for the use of farm machinery, or the soils may not respond to improvement, or the grazing season may be very short.

Class 7

Soils in Class 7 have no capability for arable culture or permanent pasture. This class includes marsh, rockland and soil on very steep slopes.

Definitions of the capability subclasses

Capability subclasses indicate the kinds of limitations present for agricultural use. Thirteen subclasses were described in CLI Report No. 2. Eleven of these Subclasses have been adapted to Ontario soils.

Subclass definitions

Subclass C: Adverse climate

Subclass C denotes a significant adverse climate for crop production as compared to the median climate, which is defined as one with sufficiently high growing-season temperatures to bring common field crops to maturity, and with sufficient precipitation to permit crops to be grown each year on the same land without a serious risk of partial or total crop failures. In Ontario, this subclass limitation is applied to land averaging less than 2300 crop heat units (CHU).

Subclass D: Undesirable soil structure and/or low permeability

Subclass D is used for soils which are difficult to till, or which absorb or release water very slowly, or in which the depth of rooting zone is restricted by conditions other than a high-water table or consolidated bedrock. In Ontario, this subclass limitation is based on the existence of critical clay contents in the upper soil profile. These soils are generally more susceptible to compaction than lighter textures soils are.

Subclass E: Erosion

Soils falling under Subclass E have been damaged by erosion and loss of organic matter, topsoil and/or subsoil has reduced productivity. In extreme situations, where erosion has caused deep gullies, use of farm machinery is obstructed.

Subclass F: Low natural fertility

Subclass F is made up of soils having low fertility that is either correctable with careful management in the use of fertilizers and soil amendments or is difficult to correct in a feasible way. The limitation may be due to:

• a lack of available plant nutrients
• high acidity
• low exchange capacity
• presence of toxic compounds

Subclass I: Inundation by streams or lakes

In soils falling under Subclass I, periodic flooding by streams and lakes causes crop damage or restricts agricultural use.

Subclass M: Moisture deficiency

Soils in Subclass M have low moisture holding capacities and are prone to droughtiness.

Subclass P: Stoniness

Subclass P indicates soils sufficiently stony to hinder tillage, planting and harvesting operations.

Subclass R: Consolidated bedrock

In soils falling under Subclass R, the occurrence of consolidated bedrock within 100 centimetres of the surface restricts rooting depth and limits moisture holding capacity. Conversely, in poorly drained soils the presence of the bedrock may, depending on depth, make artificial drainage impossible. Where physical soil data is available, the water retention model^{footnote 2[2]} was used to assist in developing the subclass criteria.

Subclass S: Adverse soil characteristics

Subclass S denotes a combination of limitations of equal severity. In Ontario, it is often used to denote a combination of F and M when these are present with a third limitation such as T, E or P.

Subclass T: Topography

Subclass T denotes limitations due to slope steepness and length. The steepness of the surface slope and the pattern or frequency of slopes in different directions are considered topographic limitations if they:

• hinder machinery use
• decrease the uniformity of crop growth and maturity
• increase the potential for tillage and water erosion potential
• increase the cost of farming the land over that of level or less sloping land

Subclass W: Excess water

Subclass W indicates the presence of excess soil moisture due to poor or very poor soil drainage. It is distinguished from Subclass I, which indicates risk of flooding from adjacent lakes or streams. Excess water may result from inadequate soil drainage, a high-water table, seepage or runoff from surrounding areas. This limitation only applies to soils classified as poorly or very poorly drained.

Information requirements

CLI classification of a soil individual requires the following data.

Soil drainage class

The soil drainage classes used in Ontario and Canada are:

• very rapid
• rapid
• well
• moderately well
• imperfect
• poor
• very poor

Thickness of unconsolidated soil material over bedrock

Depth to consolidated bedrock is required at sites where bedrock contact occurs at a depth of less than 1 metre.

Soil horizons

The type and thickness of significant soil horizons need to be identified. These include:

• depth of topsoil (Ap or Ah horizon)
• diagnostic and significant B horizons
• depth to and nature of C horizons (parent material)

Texture/particle size distribution

Textural class (mineral material <2 millimetres) for each significant horizon; gravelly modifiers to the textural class are needed where gravel content exceeds 20% by weight or 15% by volume.

Soil reaction

The depth at which free carbonates are detectable with 10% hydrochloric acid is needed in known alkaline soils. High acidity may be inferred in some soils if certain soil horizon characteristics are present such as evidence of podzolization. Soil pH testing, especially of parent materials, is also warranted if high acidity is suspected.

Slope

Slope class is based on steepness (%) and length (metres).

Surface stoniness

Surface stoniness is measured by the percentage of surface coverage of stones >15 centimetres diameter and boulders >60 centimetres diameter.

Crop heat units

The average annual CHUs for an area are determined from the general reference map for Ontario.

Location

Location means the geographic reference point of each soil profile and soil landscape inspection, as well as with respect to areas under risk of flooding by streams or lakes.

Determination of subclasses and capability ratings

Classifying a soil individual using CLI involves:

1. Identifying all subgroup limitations and the severity of each limitation (this involves the interpretation of the soil profile and landscape data using the guidelines provided in Tables 1 to 13).
2. Arriving at the final soil capability class on the basis of the most severe subgroup limitation (or limitations if 2 or more are present of equal severity).

When a soil has a single limitation, the subclass that represents that limitation is shown in the soil capability class (for example, an excess water limitation is represented by the subclass W). As a general rule, only the subclass that represents the most severe limitation is shown, since it is that limitation which has determined the capability class. In cases where 2 limitations of equal severity exist which have therefore equally determined the capability rating, both are shown in the map symbol. When a soil has more than 2 limitations of equal severity, all of the subclasses that apply to the soil are usually not shown in the class. These conventions are applied in order to simplify soil capability map units and their symbols.

Conventions in the assignment of subclasses and classes

The subclass or subclasses are denoted by capital letters placed after the class number (for example, 2P designates a Class 2 soil due to a moderate surface stoniness limitation).

A subclass is used in a classification notation only when the limitation it represents has been a factor in determining the final CLI class (for example, a soil individual or soil landscape with both a moderate stoniness limitation (equivalent to 2P) and a moderately severe topographic limitation (equivalent to 3T) would be denoted as 3T).

The subclass S is used in Ontario to represent a combination of 2 or more subclasses, when that combination is present with a third limitation of equal severity (for example, 3FMT may be denoted as 3ST).

The climatic limitation, subclass C, is applied to soil landscapes in areas which average less than 2300 CHUs. In such areas, only soils with no other limitations have the subclass C cited in their notation (for example, 2C, 3C) depending on the degree of CHU deficit less than the 2300 level. Soils of the same area but with other limitations present are first downgraded in accordance with those limitations and then further downgraded according to the degree of CHU deficit. However, the C subclass is not cited in their notation. For example, a pair of soil landscapes with no climatic limitation might classify as 1 and 2W. A pair of physically equivalent soil landscapes in an area of 1900 to 2300 CHUs would classify as 2C and 2W respectively.

When it is necessary to indicate two capability ratings because of a complex soil landscape, the relative proportion of each should be denoted in the map symbol. For example, 2P=3T, 2P>3T, or 2P⁷>3T³ where the superscript deciles indicate the relative proportion.

Soil texture class groupings

The soil texture classes have been aggregated into soil texture groups (Table 1) to enable easier definition of those subclass guidelines in which soil texture is relevant. Each soil texture group comprises an exclusive range of soil texture classes, including gravelly modifiers.

Soil reaction classes

The reaction classes have been assigned (Table 2) to enable easier definition of those subclass guidelines in which soil reaction is relevant. Each soil reaction class comprises an exclusive range of soil pH.

Subclass and class criteria

Subclass C: Adverse climate

Climate is the most important factor in considering CLI classification for the Province of Ontario. For CLI evaluation in Ontario, climate is characterized by average annual precipitation and average annual heat energy during the growing season. Annual precipitation is considered non-limiting for the whole province while heat energy and growing season length become generally more limiting with latitude. Subclass C, the climatic limitation, does not usually apply in southwestern, south-central and southeastern Ontario. The climate subclass (Table 3) is based upon the average CHU value for the area of consideration. The average CHU value is given by the CHU map in Figure 1.

If the C limitation applies in a given area, it is only cited in the classification notation of those soils present which have no other capability limitations, soils that would be Class 1 if not limited by climate. Soils of the same area with other limitations are also downgraded by the same relative degree as the best soils but the C limitation is not cited in the classification notation. For example, a soil with a moderate wetness limitation (2W) is designated 2W (but not 2CW) if it occurs in an area of 1900 to 2300 CHUs.

Subclass D: Undesirable structure and/or low permeability

Subclass E: Erosion

Subclass F: Low natural fertility

Subclass I: Inundation by streams or lakes

Subclass M: Moisture deficiency

Subclass P: Stoniness

Subclass R: Shallowness to consolidated bedrock

Subclass T: Topography

The surface texture of the soil being assessed should be used to assign this limitation using the texture class groupings outlined in Table 1.

Subclass W: Excess water

CLI data input and rating tables

Download a PDF worksheet for fillable versions of the CLI data input and rating tables.

CLI rating examples

Bennington soil series

CLI rating

Brookston soil series

CLI rating

Otonabee soil series

CLI rating

Kars soil series

CLI rating

Fox series

CLI rating

Glossary

Ap horizon

The surface horizon of a mineral soil where organic matter has accumulated, and then been disturbed by clearing and cultivation (plough layer).

B horizon

A weathered soil horizon of a mineral soil beneath the A horizon and characterized by one or more of the following:

• enrichment in silicate clay, iron, aluminum or organic matter
• alteration by hydrolysis, oxidation or reduction to give a change in colour, structure or both from the horizons above or below

Bt horizon

B horizon characterized by enrichment of silicate clay as indicated by a higher clay content than the eluviated soil layer above it.

Calcareous soil

A soil containing sufficient calcium carbonate and magnesium carbonate to effervesce carbon dioxide when treated with 10% hydrochloric acid.

Cation exchange capacity

The total amount of exchangeable cations that a soil can absorb.

Ck horizon

C horizon comprising relatively unweathered parent material containing calcium carbonate and magnesium carbonate that is easily detectable with 10% hydrochloric acid.

Coarse fragments

Mineral particles which are greater than 2.0 millimetres in diameter. Includes gravel, cobbles and boulders.

Crop heat units (CHUs)

Values which provide an index of the average total climatic heat energy available for the growth and maturity of warm season crops.

Eolian

Sediments transported and deposited by wind.

Erosion

The wearing away of the land surface by running water, wind, ice or other geological agents, such as gravitational creep.

Field capacity

The amount of water remaining in a soil that has been saturated and then allowed to freely drain.

Floodplain

Nearly level land situated on either or both sides of a channel that is subject to overflow flooding; flood prone alluvial areas adjoining inland or coastal waters; floodprone areas of islands.

Gully

A channel which has been caused by erosion due to the convergent flow of heavy water runoff and which interferes with machinery operation.

Igneous rock

Rock formed by the cooling and solidification of magma. In the Canadian Shield, such rock is usually high in silica, resistant to weathering and acidity.

Marsh

Continuously inundated wetland areas supporting hydrophytic vegetation; can include shallow standing water (<0.5 metre depth).

Metamorphic rock

Rock derived from pre-existing rocks, but differing from them in physical, chemical and mineralogical properties as a result of natural geological processes, principally heat and pressure, originating within the earth.

Mineral soil

A soil consisting predominantly of, and having its properties determined predominantly by mineral matter (sand, silt, clay and coarse fragments). Horizons must contain <30% organic matter by dry weight, with the exception of the surface layer which may exceed 30%, if it is <40 centimetres thick and comprised of moderately to well (mesic or humic) decomposed peat, or <60 centimetres thick and comprised of fibric peat.

Organic soil

A soil composed primarily of decomposed or partly decomposed plant and animal materials. As such, it contains >30% organic matter by dry weight. The total depth of the organic material must exceed 40 centimetres if the soil is moderately to well decomposed (mesic or humic), or >60 centimetres if the material is poorly decomposed (fibric).

Pedology

The aspects of soil science dealing with the genesis, distribution, mapping, taxonomy and interpretation of soils.

pH

A measure of the acidity or hydrogen ion activity of a soil. It is used as an indicator of the acidity or alkalinity of soils. The pH of Ontario soils ranges from extremely acid to moderately alkaline (pH range 4.0 to 8.0).

Porosity

The percent volume of the total bulk soil that is not occupied by solid particles.

Rill

A small intermittent water course only a few centimetres wide. Rills do not interfere with tillage or other machinery.

Sedimentary rock

Rock formed by the lithification of mechanical, chemical or organic sediments. The principal sedimentary rocks are sandstones, shales, limestones and conglomerates.

Soil classification

The systematic arrangement of soils into categories on the basis of their characteristics. Broad groupings are made on the basis of general characteristics, and subdivisions on the basis of more detailed differences in specific properties.

Soil drainage

As a description of the natural condition of the soil, soil drainage refers to the frequency and duration of periods during which the soil is free of saturation. In a well-drained soil, excess water (gravitational water) is removed readily but not rapidly. By contrast, in a poorly drained soil, the root zone is saturated for long periods unless it is artificially drained. In a very rapidly drained soil, water is removed very rapidly in relation to supply and most crop plants suffer from lack of water.

Soil fertility

The status of a soil in the relation to the amount and availability to plants of elements necessary for plant growth.

Soil horizon

A distinct layer of soil, approximately parallel to the ground surface, within a soil profile. It differs from adjacent genetically related layers in properties such as:

• colour
• structure
• texture
• consistence
• chemical composition
• biological composition
• mineralogical composition

In soil surveys, the soil horizons comprising soil profiles are usually logged to depth of at least one metre. Generally, a soil horizon should be more than 5 centimetres thick to be considered as significant to soil profile characterization.

Soil map unit

A kind of soil, or a combination of kinds of soils that can be shown as a delineation or polygon on a soil map.

Soil morphology

The physical constitution of a soil exhibited by the kinds, thicknesses and arrangements of the soil horizons comprising the soil profile.

Soil organic matter

The organic fraction of the soil which includes plant and animal residues at various stages of decomposition. Expressed as a percentage of dry soil weight.

Soil pedon

The basic soil profile sampling, description and classification unit at a representative site in a soil landscape. A soil pedon can be classified by soil series plus any applicable phases.

Soil permeability

The ease with which gases or liquids penetrate or pass through the soil.

Soil profile

A vertical section of the soil through all its horizons and extending into the parent material.

Soil reaction

The degree of acidity or alkalinity of a soil usually expressed as a pH value.

Soil structure

The aggregation and arrangement of primary soil particles (sand, silt, clay, organic matter) into discrete soil peds or aggregates.

Soil texture

The relative proportions by weight of the various particle size fractions in the mineral fraction of the soil (sand, silt, clay), as described by the soil texture classes. The sand fraction is further subdivided into coarse sand, sand, fine sand and very fine sand, based on the proportions of various sand sizes within the sand fraction. Therefore, loamy sand textures can be more precisely described as loamy coarse sand, loamy sand, loamy fine sand and loamy very fine sand, as the case may be. Likewise, the sandy loam textures can be classified as coarse sandy loam, sandy loam, fine sandy loam, and very fine sandy loam. When the gravel percentage present is between 20 and 50% by weight (equates to approximately 15 to 35% gravel by volume) the texture class is gravelly for example, gravelly sandy loam, gravelly loam). When the gravel fraction exceeds 50% (>35% volume), a very gravelly descriptor is used (for example very gravelly sandy loam, very gravelly sand).

References

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Canada Department of Agriculture, Environment Canada, 1967-74, Soil Capability for Agriculture Map Series; Scale 1:250,000

Expert Committee on Soil Survey. 1981. A Soil Mapping System for Canada: Revised. Research Branch, Agriculture Canada.

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Leeson B. 1969. An Organic Soil Classification for Agriculture and a Study of the Organic Soils of Simcoe County. Dept. of Soil Science, University of Guelph.

Mathur, S. P., and M. P. Levesque. 1987. A Revised Capability Rating Scheme for Organic Soils in Canada. Centre for Land and Biological Resources Research, Research Branch, Agriculture Canada, Ottawa.

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McBride, R. A. and E. E. Mackintosh. 1984. Soil survey interpretations from water retention data: II. Assessment of soil capability ratings and crop performance indicies. Soil Sci. Soc. Am. J. 48:1343-1350.

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Ontario Ministry of Municipal Affairs and Housing. 1997 Provincial Policy Statement

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