| | Soil-forming factors | Soil profiles | Dominant soils within Alberta’s ecoregions | Soil use
This document is part of the Agroclimatic Atlas of Alberta.
Soil properties are strongly influenced by climate. They are also affected by other ecoregion factors, such as physiography, vegetation, water and land-use.
Both climate and soils data are essential for making many agricultural decisions. For example, the local climatic conditions may be appropriate for a certain crop type, but perhaps the soil has a low moisture-holding capacity that would limit the yield of this crop type.
This chapter provides a general guide to understanding Alberta’s agricultural soils to complement the climate information provided in the Atlas. This general understanding creates a foundation for using the more detailed soils information required when making decisions for a specific farm.
Detailed soil survey information for the agricultural region of Alberta is available in digital format in AGRASID (Agricultural Region of Alberta Soil Inventory Database; scale 1:100,000).
Soil-Forming Factors
Soils are vital to support and sustain crop, range and woodland production as well as to maintain or enhance environmental quality. Soils serve as a medium for plant growth, in the regulation of water supply, in recycling of wastes, as a habitat for organisms and as a support for human infrastructure.
Soils are dynamic and evolve over long periods of time. Factors controlling the formation of soils include climate, vegetation, parent material, topography and time. Human activities, such as soil management, may also be considered a soil-forming factor.
Climate and associated vegetation play a significant role in soil formation. Differences in climate (especially precipitation and temperature) and associated native vegetation are reflected in different ecoregions (see Figure 4).
Moving from southeast to northwest Alberta, the available moisture generally increases and the temperature generally decreases, resulting in a change in associated vegetation. The Mixed Grassland ecoregion, in the southeast corner, is characterized by a semiarid climate and short grass prairie native vegetation. As you proceed north and west, the increased moisture results in more vigorous growth of grasses in the Moist Mixed Grassland and Fescue Grassland ecoregions. Farther north and west, fescue grasslands interspersed with aspen groves typify the Aspen Parkland. Proceeding farther north, the Boreal Transition is characterized by a deciduous and coniferous forest. The Peace Lowland is characterized by grassland and forest vegetation.
The colour and depths of the upper soil layers reflect climate, vegetation and organic matter accumulation. In the grassland areas, organic matter has been added to the soil mainly through plant roots, resulting in upper soil layers high in organic matter. In the Mixed Grassland, brown surface colours occur in association with short grass vegetation in a dry climate. The darker brown and black colours of the Moist Mixed Grassland and Aspen Parkland occur with the higher organic matter content from the thicker stands of grasses in more humid areas. In forested areas, organic matter is added as a surface deposit of leaves and needles, resulting in leached upper soil layers low in organic matter and light gray in colour.
Parent material is the unconsolidated material in which soils develop. Parent materials were deposited through the actions of ice, wind, water or gravity. For example, materials deposited by glacial ice are referred to as glacial till; gravels, sands and silts deposited by moving water are fluvial deposits; sand or silt deposited by wind are eolian deposits; and materials moved by water and deposited in lakes are referred to as lacustrine deposits.
Properties of soil such as texture and mineral elements are inherited from the parent materials. Most of the soils in central Alberta have developed on glacial till, while most of the soils in the Peace Lowland region have developed on glaciolacustrine material (deposited from glacial lakes). Till is generally medium textured (loam). Coarse textured soils (sands) are generally associated with fluvial or eolian deposits. Finer textured soils (clays) are generally associated with lacustrine or glaciolacustrine deposits.
Topographic factors, such as elevation and slope aspect, affect soil-forming factors like moisture and vegetation, resulting in different types of soil. The shape of the landscape affects drainage patterns that in turn affect the type and amount of vegetation. Generally, soil is driest on knolls and wettest in depressions. North-facing slopes are usually cooler and moister than south-facing slopes.
Management practices such as crop rotations and tillage methods can influence soil formation. Crop rotations that incorporate forages as well as annual crops in conjunction with reduced tillage increase the amount of soil organic matter. The increased organic matter content alters the soil's physical properties like aggregation and infiltration in the upper soil layers
Soil Profiles
The combined effects of soil-forming factors result in the formation of horizontal soil layers, called soil horizons. The soil horizons extend from the soil surface to the unaltered parent material. The succession of soil horizons is referred to as a soil profile. Usually the soil profile is described to a depth of 1 m.
Different horizons develop as a result of additions (organic matter from plants and animals, water), transfers within the soil profile (leaching, loss of nutrients, movement of materials such as clay, organic compounds or minerals) and transformations (through chemical and biological reactions).
Soil horizons are identified as either mineral or organic. The three main mineral horizons are A, B and C. The A horizon is at or near the surface and usually has the most organic matter accumulation. The B horizon is below the A horizon. It usually has an enrichment or alteration of some materials, such as clay, and has more structure than the A horizon. The C horizon, closest to the parent material, is relatively unaffected by soil-forming processes. However, calcium carbonates (lime) and salts can accumulate in this horizon.
The three main organic horizons are referred to as L, F, and H layers, also known as the leaf layers. The L-F-H layers occur in forest soils, at the surface of mineral horizons. They are the accumulation of leaves, twigs and woody materials at various stages of decomposition.
Dominant Soils within Alberta’s Ecoregions
Soil classification or identification is based on the soil profile and its sequence of soil horizons. Soil orders, such as Chernozemic, Luvisolic, Gleysolic and Regosolic, are identified based on the effects of the dominant soil-forming processes or factors.
The Mixed Grassland is dominated by Brown Chernozemic soils, the Moist Mixed Grassland by Dark Brown Chernozems, and the Fescue Grassland and Aspen Parkland by Black Chernozems. Chernozemic soils, typical of grassland soils, are well to imperfectly drained. Soil profiles have brown to black A horizons with brownish B horizons and are underlain by light-coloured C horizons with lime accumulations. Depth to lime is a reflection of moisture penetration. Lime is generally present at 100 to 120 cm deep in central and northern Alberta, while in southern Alberta lime is present at 30 to 40 cm deep.
The Boreal Transition ecoregion is dominated by Luvisols, which are forest soils. These soils are developed under the influence of forest vegetation and are well to imperfectly drained. Soil profiles have a leached, light grayish A horizon and a B horizon enriched with clay. Chernozems and Luvisols dominate the Peace Lowland ecoregion.
Other soil orders can occur in association with Chernozems and Luvisols in the landscape. For example, Gleysols are soils that are poorly drained at some time of the year. These soils often occur in depressions or at lower slope positions. Solonetzic soils are commonly associated with Chernozems through east central Alberta. These soils are well to imperfectly drained and developed on saline parent materials. They are characterized by having a dense impermeable B horizon that limits both water penetration and root development. Regosolic soils are well to imperfectly drained and are considered young soils due to their development. Soil profiles of this order do not have a B horizon and have a thin or no A horizon; usually only the C horizon is present.
Soil Use
Alberta has 30 per cent of the arable land in Canada. The three Prairie Provinces account for 80 per cent of the agricultural land base of Canada.
According to the 1996 Census of Agriculture, the proportion of total Alberta farmland that was cultivated varied from 52 per cent in the Moist Mixed Grassland and 54 per cent in the Aspen Parkland, to only 24 per cent in the Boreal Transition. Nearly 37 per cent of the total farmland in the Mixed Grassland and 45 per cent in the Peace Lowland was cultivated. Only a small portion of soils outside the agricultural area is cultivated.
In the 1996 Census, the total number of farms in Alberta was close to 58,000, and the total land area of farms was greater than 20 million hectares. Of the total area farmed, 46 per cent was in crops, 6 per cent in summerfallow, and 42 per cent in natural or seeded pasture. The remaining 6 per cent was in a wide variety of uses such as farmyards, gardens, greenhouses, Christmas trees, woodlots, and wetlands. Cultivated land is dominated by the production of cereal crops, especially wheat and barley. However, the area planted to oilseeds, forages and pulse crops is increasing.
Nearly four times as many hectares of summerfallow occurred in the Mixed Grassland and Moist Mixed Grassland, where soil moisture is relatively low, compared to the summerfallow hectares in the Aspen Parkland, Boreal Transition and Peace Lowland where soil moisture is higher. In contrast, the Aspen Parkland, Boreal Transition and Peace Lowland had nearly eight times the area in hay and forage as the Mixed Grassland and Moist Mixed Grassland ecoregions. |
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