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a Semiarid Prairie Agric. Res. Cent., Agric. and Agri-Food Canada, 51 Campus Drive, Saskatoon, SK, S7N 5A8 Canada
b USDA-NRCS, Lincoln, NE 68508-3866
c Dep. of Land Resour. and Environ. Sci., Montana State Univ., Bozeman, MT 59717-3120
d Lethbridge Res. Cent., Agric. and Agri-Food Canada, Lethbridge, AB, T1J 4B1 Canada
e Dep. of Agron. and Hortic., Univ. of Nebraska, Lincoln, NE 68583-0953
* Corresponding author (padburyg{at}em.agr.ca)
Received for publication December 18, 2000.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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Abbreviations: masl, meters above sea level
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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Agronomic research is typically carried out under controlled conditions either at a small-scale research plot or, to a lesser extent, under field conditions at a larger scale. As such, the results or research findings need to be extrapolated to the surrounding countryside where conditions often differ significantly. Land resource inventories, or soil surveys, provide an inventory of land-related characteristics of a region and are fundamentally carried out to facilitate the extrapolation of information from the research site to like conditions elsewhere. Conceptually, the research procedure is generally as follows: Agronomic research is first carried out under controlled conditions resulting in a particular finding or findings. Based on the finding(s), a model is developed to predict what comparable finding(s) would be under the breadth of conditions (soil, climate, and management) found in the region. Finally, the land resource inventory documents where specific conditions occur or in other words, provides spatial information to apply the model and effect the extrapolation.
This paper documents the distribution of the major land resource areas, or agroecoregions, of the northern Great Plains and provides an initial framework for the extrapolation of pertinent agronomic information from the research site to areas of similar environmental conditions. Each agroecoregion is described in terms of its soil and landscape characteristics, with a particular focus being given to likely key environmental parameters related to the production of oilseed, pulse, and forage crops being introduced in the region. Climate data are provided for a few specific climate observation stations within each agroecoregion (Table 1).
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GENERAL DESCRIPTION OF THE NORTHERN GREAT PLAINS |
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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The climate of the northern Great Plains is continental, characterized by long, cold winters; short but warm summers; large diurnal ranges in temperature; frequent strong winds; and, from an agricultural perspective, most importantly by highly variable and unpredictable precipitation. Annual precipitation varies mostly from 300 to 500 mm, but extreme year-to-year variations are common and long spells of hot, dry weather characterize much of the summer. In general, fluctuations in climate often create serious risks to agriculture, with the uncertainty of precipitation and the extremes of temperature being the most common crop hazards (Nuttonson, 1965; Ecoregions Working Group, 1989).
Native vegetation of the northern Great Plains is largely open grassland characterized by drought-tolerant short and medium grasses. In the southern and eastern parts, woody vegetation is confined mostly to valley bottoms and along major streams although scattered ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & Lawson) is found at higher elevations. A mosaic of aspen groves and fescue grasslands characterizes the parkland regions while mixed-wood forests are found along the northern boundary. The defining characteristic of most soils is the high (2–8%) organic matter content of the topsoil (Nuttonson, 1965).
For this paper, the northern Great Plains is taken to include the agricultural regions of South Dakota, North Dakota, and Montana; parts of northeastern Wyoming and northwestern Nebraska; the arable regions of the Canadian provinces of Manitoba, Saskatchewan, and Alberta; and northeastern British Columbia (Fig. 1) . From an agronomic perspective, it has long been thought of as the area where hard red spring wheat is the dominant crop and where drought is the most common factor limiting production (Tables 1 and 2). In general, it is bounded on the south by the winter wheat region of the Southern Great Plains and on the east by the more humid corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] country of Nebraska, Iowa, and Minnesota. Its northern boundary marks the northern limit of arable agriculture.
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AGROECOSYSTEMS IN RELATION TO CROPPING SYSTEMS |
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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AGROECOREGIONS OF THE NORTHERN GREAT PLAINS |
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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Compilation of an agroecoregion map inevitably involves deciding what components are most important and how boundaries are to be determined. The ecological approach implies an interaction among components (e.g., soils, vegetation, and climate), but all components are not equally significant. Climate, for example, is unquestionably the prime ecological factor in the northern Great Plains. As climate changes, other components of the system change in response. This is clearly displayed throughout the northern Great Plains where the climate gradient, which is governed largely by latitude and proximity to the Rocky Mountains, is matched by a change in both the native vegetation and related soil types to form distinct ecological zones (Bailey, 1995).
Setting agroecosystem boundaries involves dividing the landscape where environmental conditions exhibit a significant change when compared with adjacent areas. In essence, it is a classification of space where one is concerned about conditions that prevail over some unit area, specifically those conditions that are important to agriculture production. The present framework identifies 14 agroecoregions within the northern Great Plains. And while the areas themselves approximate the above-mentioned broad ecological or climatic zones, it is important to recognize that the specific boundaries on the map are often set according to regional soil conditions (soil organic matter levels) or native plant communities as expressed by macrofeatures of vegetation (e.g., grassland or forest). In such cases, the soils and vegetation are, in essence, considered to be indices of long-term climatic influence (Bailey, 1995).
Because land resources do not suddenly change along the USA–Canada border, existing data from each country has been used to define the agroecosystems without regard to the political boundary. On the Canadian side, the agroecoregion boundaries closely follow those outlined in A National Ecological Framework for Canada (Ecological Stratification Working Group, 1995). On the USA side, agroecoregion boundaries result from grouping several geographically related Major Land Resource Areas into broader regions (USDA, 1981).
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AGROECOSYSTEM DESCRIPTIONS |
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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In the northern part of Agroecoregion 1, the soils (Ustolls, Orthents, and Psamments, frigid) (Soil Survey Staff, 1999) are shallow to deep, well drained, and sandy to clayey textured and are formed in siltstone and shale bedrock, soft sandstone bedrock, weakly consolidated silty and sandy sedimentary beds, alluvium, and glacial till. The slopes are nearly level to very steep. Some soils have measurable amounts of salt, and a few have a Na adsorption ratio >20 in the subsoil. A few have measurable amounts of calcium carbonate (CaCO3) in the topsoil. This moderately dissected rolling plain is underlain by soft calcareous shale, siltstone, and sandstone. Buttes, badlands, and moderately steep to very steep slopes are adjacent to major valleys. Badlands are generally characterized by an intricately dissected, high-density drainage network with short, steep slopes and narrow interfluves resulting from erosion of soft geologic materials, and they are generally devoid of vegetation (SSSA, 1996). The northern and eastern parts have glacially modified topography.
Most soils (Orthents, Orthids, Ustalfs, Ustolls, and Fluvents, frigid) in the west-central part of this agroecoregion are shallow to deep, well drained, loamy, and clayey textured and are formed in residuum from sandstone, siltstone, and shale; weakly consolidated silty and sandy sedimentary beds; interbedded siltstone, sandstone, and shale; and alluvium. The slopes are nearly level to very steep. Some of the soils have measurable amounts of salt, and a few have Na adsorption ratios >40 in the subsoil. Dissected plains are underlain by shale, siltstone, and sandstone. Wide belts of steeply sloping badlands border a few of the larger valleys. In places, flat-topped, steep-sided buttes rise above the general level of the plains.
In the northeastern part of Agroecoregion 1, most soils (Orthents and Psamments, frigid) are shallow to deep, well drained, sandy, and loamy. They formed in weakly consolidated silty and sandy sedimentary beds, residuum weathered from soft sandstone, or sandy eolian material. The slopes are gently sloping to very steep. Some of the loamy soils have measurable amounts of salt and Na adsorption ratios >50 in the subsoil. Dissected plains are underlain by siltstone and sandstone. Wide belts of steeply sloping badlands border a few of the larger valleys. In places, flat-topped, steep-sided buttes rise above the general level of the plains.
In the east-central part of Agroecoregion 1, most soils (Orthents, Orthids, Argids, Ustolls, and Fluvents, frigid) are shallow to deep, well drained, and sandy to clayey textured and are formed in residuum from limey sandstone, weathered soft sandstone, and silty and clayey shale interbedded with sandstone, weakly consolidated silty and sandy sedimentary beds, alluvium, and sandy eolian material. Some of the soils have measurable amounts of salt, and a few have Na adsorption ratios >50 in the subsoil. A few of the soils have measurable amounts of calcium carbonate. These dissected plains are underlain by shale and sandstone. Slopes are mostly gently rolling to very steep. In places, flat-topped, steep-sided buttes rise sharply above the general level of the plain.
In the south-central part of Agroecoregion 1, most soils (Orthents and Usterts, frigid) are shallow and moderately deep, well drained, and clayey textured and are formed in alluvium or residuum from shale and claystone. The slopes are nearly level to very steep. Most soils have measurable amounts of salt, and a few have Na adsorption ratios >50 in the subsoil and measurable amounts of calcium carbonate. These shale plains have long, smooth, and gentle to strong slopes. Slopes along drainage ways and streams are moderately steep to very steep.
Approximately 58% of the land area is rangeland or improved pasture, and 18% of the land is in cropland. This pattern shifts from east to west. The westernmost extent of this region is almost exclusively rangeland. Narrow strips of irrigated land along the Missouri and other rivers enable the production of irrigated alfalfa (Medicago sativa L.), sugarbeet (Beta vulgaris L.), corn, and feed grains, but there is little potential for further irrigation development.
Agroecoregion 2
This agroecoregion occurs east of the Red River valley, extending from northeastern South Dakota through North Dakota into southwestern Manitoba and southeastern Saskatchewan (Fig. 1). The local landscape is mainly a hummocky glacial till plain having low local relief and numerous small, undrained depressions or sloughs. The exceptions on the Canadian side are the steeply sloping and largely forested Moose Mountain upland, a small area of clayey glaciolacustrine sediments along the Qu'appelle Valley, and a few sandy glaciofluvial deposits scattered along the Souris and Assiniboine river valleys. In the southern part, the landscapes are generally level to undulating glacial till and glacial lake plains, and the bulk of the arable soils are Udic Ustolls (Black Chernozems) (Soil Classification Working Group, 1998) developed on loamy-textured glacial till and, to a lesser extent, on clayey lacustrine deposits and sandy eolian materials. Aquolls (Gleysolics) occur in the poorly drained depressions (Smith et al., 1998).
This agroecoregion spans a distance of more than 500 km north to south, which leads to a rather wide range of climate conditions. Mean annual temperature ranges from >5°C in the south to about 1.5°C in the north while the frost-free growing period ranges from 120 to 140 d in northern South Dakota to slightly more than 100 d in the aspen parkland near Indian Head in southern Saskatchewan. Precipitation ranges from 375 to 500 mm annually, with about half of that amount coming during the growing season.
Nearly all of the land is farmland, and about 75% is seeded annually. Cereals account for slightly over half of the cropland, with hard red spring wheat, barley (Hordeum vulgare L.), and oat (Avena sativa L.) being the most common crops (Table 2). Spring wheat is dominant in the southern parts along with a small area of corn and sunflower (Helianthus annuus L.). In the northern parts, about 15 to 20% of the cropland is seeded to oilseeds, mainly canola (Brassica napus), and between 5 and 10% is seeded to specialty crops, most notably pea (Pisum sativum L.). These crops are commonly found in rotation with cereals. Another 10% of the area is seeded to perennial forages, which often form part of longer rotations. Over the past decade or so, there has been a significant increase in oilseeds, forages, and specialty crops and a corresponding decrease in summer fallow, which now accounts for only about 10% of the cropland annually (NASS, 2000; Anderson et al., 1999; Baltensperger et al., 1999). Relatively warm temperatures and a long growing season offer opportunities for diversification.
Agroecoregion 3
This agroecoregion comprises a narrow band along the Red River valley, stretching northward along the North Dakota–Minnesota border to Winnipeg, MB, and then northwestward along the east side of the Manitoba Escarpment and as far as Lake Dauphin (Fig. 1).
In the northern part, the glacial till deposits form a distinct north-south trending ridge and swale pattern, with ridges comprised largely of moderately coarse-textured, strongly calcareous, and often cobbly glacial till and the depressions containing shallow finer-textured glaciolacustrine and alluvial deposits. The soils on the ridges are Udic Ustolls (Rego Black) and imperfectly drained Aquerts (Gleyed Rego Black Chernozems). Aquerts are also found in the swales along with poorly drained Aquolls (Gleysolic) soils, with the latter often having a shallow layer of peat at the surface. Crop production in this part of the region is severely limited due to the generally shallow, infertile, and poorly drained nature of these soils (Smith et al., 1998).
Most of the region, however, is found along the Red and Assiniboine rivers where the topography is level to gently sloping due to the thick (up to 60 m) deposits of silts and clays of former glacial Lake Agassiz. On the clays, imperfectly drained Cryerts (Vertisols) predominate while Udic Ustolls (Rego Black Chernozems) are more common on the slightly coarser-textured deltaic and lacustrine sediments as well as on some of the sandy outwash deposits bordering the lake plain. The level landscape and highly impervious nature of the clayey soils contribute to periodic flooding along the Red River and its tributaries, the most recent occurrence being in 1998. In fact, local flooding and excess wetness is a significant problem in many years.
The climate here is slightly warmer and more humid than in the aspen parklands to the north and west. Annual precipitation averages about 500 mm, with about half occurring during the April-to-July growing season, while the mean annual temperature is about 4 to 5°C and the frost-free season usually exceeds 125 d (Table 1). Ecologically, this region represents a transition between the more humid tallgrass prairie to the east and the drier shortgrass prairie to the west. Before settlement, the area was a mosaic of trembling aspen (Populus tremuloides Michaux)–oak (Quercus spp.) groves and fescue grasslands, but little native vegetation remains apart from the woody vegetation found along steeply sloping stream channels and in poorly drained wetlands.
In the southern part, more than 80% of the land is cropped annually, and there is almost no summer fallow. Spring wheat is still the major crop, but the area is rapidly becoming more diversified, with increased production of oat, barley, canola, and flax (Linum usitatissimum L.) along with a variety of forages and specialty crops such as sugarbeet. There is also a small but steadily increasing amount of potato (Solanum tuberosum L.), corn, and a variety of garden crops being produced under irrigation. The combination of a level landscape, fertile clay-textured soils, and, most importantly, a relatively warm, humid climate make this agroecoregion arguably the most productive in the northern Great Plains and one in which there is opportunity for further diversification.
Agroecoregion 4
This ecoregion is typified by native shortgrass prairie characterized by green needlegrass (Stipa viridula Trin.), western wheatgrass [Elymus smithii (Rydb.) Gould], blue grama [Bouteloua gracilis (Willd. ex Kunth) Lagasca ex Griffiths], and needle-and-thread grass (St. comata Trin. & Rupr.). The region normally receives 350 to 425 mm of rainfall annually, an amount often inadequate for maximum crop production. With the declining precipitation from east to west across the northern High Plains, the proportion of the area under crop production generally decreases. In contrast to the eastern edge of the adjoining Agroecoregion 2, the proportion of cropland area declines from 65 to 45%.
Most of the soils (Ustolls, frigid) are deep, well drained, and loamy and are formed from glacial till. The level and depressional poorly and very poorly drained soils are formed in water-sorted sediments, local alluvium, and glacial till. The soils are nearly level to steep. A few of the soils have Na adsorption ratios >15 in the subsoil. Some of the soils have compact glacial till in the subsoil, thus reducing the soil volume for plant root exploration. These nearly level to gently rolling till plains include many areas of potholes. Moderately steep to very steep slopes are adjacent to major valleys.
The bulk of this agroecoregion is under farm or rangeland management. Spring wheat is the predominant crop although other dryland cereals such as barely and oat are also grown. With the exception of the large irrigation development north of Williston, ND, irrigation is confined mainly to the Missouri River valley where irrigated alfalfa is grown on some farms to support the local livestock industry.
Agroecoregion 5
This agroecoregion is comprised of a typical shortgrass prairie with a number of tallgrass species like big bluestem (Andropogon gerardii Vitman) found in less well-drained soils. Annual precipitation ranges from 375 to 500 mm. Most of the soils (Ustolls, mesic) in the northwestern part are deep, loamy, moderately well or well drained, and formed in glacial till and silty and clayey alluvium. The level and depressional poorly drained soils are formed in clayey alluvium. Most soils are nearly level and gently sloping, with some ranging to steep. Some of the soils have compact glacial till in the subsoil, thus reducing the soil volume for plant root exploration. A few of the soils have measurable amounts of salts. These nearly level to gently rolling till plains include many areas of potholes. Moderately steep to very steep slopes are adjacent to major valleys.
Most of this agroecoregion is in agriculture, with slightly more than 50% of the land under crop production. The principal crops grown in the region include corn, oat, wheat, and sorghum [Sorghum bicolor (L.) Moench]. Annual precipitation is often inadequate for maximum yields, and access to quality ground water and surface water for irrigation is limited to a narrow band along the Missouri River.
Agroecoregion 6
Most of the soils (Orthids, Orthents, Usterts, Ustolls, and Fluvents, mesic) are very shallow to deep, well drained, and clayey and are formed in soft shale bedrock, with the remainder forming in eolian and alluvial materials. For the most part, the shale plains have long, smooth slopes with a well-defined dendritic drainage system. The badlands consist of eroded walls and escarpments; small, relatively level grass-covered tablelands and mesas; and basins in which there are scattered, eroded buttes. In contrast to the Southern Glaciated Plains to the east, the bulk of this agroecoregion is nonarable, with more than 60% being rangeland. Only about 10% is cultivated, and the main crops are alfalfa, sorghum, and hay, which are grown to support the local livestock industry (USDA, 1992; NASS, 2000).
Agroecoregion 7
This ecoregion extends from eastern Wyoming to just across the border with eastern Montana where the land area is dominated by grassland vegetation. Rainfall is typically 300 to 475 mm annually and varies greatly from year to year. Most of the soils (Orthents, Orthids, Argids, and Fluvents, mesic) are shallow to deep, well drained, loamy to clayey and formed in soft bedrock and alluvium. They are nearly level to very steep. These dissected plains are underlain by shale and sandstone. Slopes are mostly gently rolling to steep, and wide belts of steeply sloping badlands border a few of the large valleys. In a few places, flat-topped, steep-sided buttes rise sharply above the general level of the plain.
Approximately 75% of the area is native ranchland used for beef cattle (Bos taurus) and sheep (Ovis aries) production. Grain crop production is limited to river bottoms and sloping deep soils where dryland spring wheat is grown (approximately 5% of the land area). In the river bottoms of the Platte, Tongue, and Powder rivers, narrow strips of land produce irrigated alfalfa, hay, and feed grains. Outside of the irrigated area in river bottoms, low and erratic precipitation is the principal source of water for agriculture.
Agroecoregion 8
Most of the soils (Ustolls and Torriorthents mesic) in the western part are shallow to deep; excessively and well drained; and sandy, loamy, and silty in texture. The soils are formed in soft bedrock, loamy alluvial, sandy eolian materials, and loess. The soils formed in loess have the highest available water capacity for plant growth. The nearly level to gently sloping tableland south of the narrow, steep-walled valleys of Pine Ridge has the highest elevation. The topography north of the Pine Ridge escarpment is strongly sloping but becomes less sloping as distance from the escarpment increases. Local relief is mainly a few meters, but at Pine Ridge, relief is tens of meters.
The higher parts of the tableland are nearly level to moderately sloping, but steeper sections are on the sides of ridges and drainageways. Drainages are well defined in some undulating areas where eolian sandy materials mantle the bedrock.
Approximately 75% of the land area is native rangeland supporting beef cattle and sheep production. Cropland is confined to river bottoms and sloping deep soils. Dryland spring wheat is grown on approximately 5% of the land area while a small amount of irrigated alfalfa, hay, and feed grains are produced along the Platte, Tongue, and Powder rivers. Outside of the limited land area in river bottoms, low and erratic precipitation is the principal source of water for agriculture (USDA, 1992; NASS, 2000).
Agroecoregion 9
This agroecoregion is comprised of a long, narrow, convoluted area stretching more than 500 km along the foothills of the Rocky Mountains from southern Alberta to southern Montana (Fig. 1). Elevations range from 900 to 1200 masl in Alberta, increasing gradually to 1100 to 1800 masl in northern Montana and to as high as 2400 masl in southern Montana near the Wyoming border. The northern parts are characterized by undulating to rolling, loamy glacial till and clayey, lacustrine deposits underlain by sandstones and shale. In Montana, the landscapes are more diverse, with many narrow valleys having steep gradients that cut into the rugged hills and low mountains. Broad flood plains and fans border a few of the major rivers.
Due to moderating chinook conditions along east-facing slopes of the Rocky Mountain foothills, the winters are relatively warm. The summers are also warm, but the average frost-free period is only about 80 d at the highest elevations. Average annual temperature is 6 to 7°C. Average annual precipitation is mainly 300 to 500 mm but can be as high as 750 mm at the highest elevations and as low as 250 mm in some basins. In the north, most precipitation is in spring while in the south, it is early in summer.
Native vegetation in the north is largely grassland in the valleys and foothills and forest at the higher elevations. The thick grass sward and black soils are similar to those found in central Alberta, but trees are found only in sheltered locations along some waterways. This grassland community is dominated by rough fescue (Festuca altaica Trin.), with lesser quantities of oat grass (Danthonia parryi), June grass (Koeleria cristata), and wheatgrass. Drier sites have increased amounts of needle-and-thread grass. To the south, the grassland vegetation shifts to bluebunch wheatgrass [Elytrigia spicata (Pursh) D.R. Dewey], rough fescue, Idaho fescue (F. idahoensis Elmer), and western wheatgrass while at the higher elevations, the forests are dominated by ponderosa pine, Rocky Mountain juniper (Juniperus scopulorum Sarg.), and common snowberry (Symphoricarpus occidentalis).
The soils are mostly (Ustolls, Orthents, and Fluvents, frigid) shallow to deep, well and moderately well drained, and loamy and clayey. In Alberta, they occur on nearly level to very steep slopes and are formed in glacial till and lacustrine materials while alluvium and hard to weakly consolidated bedrock (sandstone, shale, and igneous) are the dominant soil parent materials farther south.
The bulk of the arable land occurs north of the 49th parallel, with barley and, to a lesser extent, wheat and canola being the main crops. Along the Canada–USA border, a mix of cultivation on the flatter portions and ranching on the rougher ridged uplands and foothills is common. About 20% of the land is federally owned, with the remainder in farms and ranches. One-half or more of the area is range. Many of the valleys are irrigated, but they make up only 1 or 2% of the total area. Grain and forage for livestock are the main crops, but potato, sugarbeet, and pea are grown in the warmer valleys. About one-fifth of this agroecoregion, mainly along the northeastern side south of the 49th parallel, is in dryland wheat production.
Agroecoregion 10
This agroecoregion extends in a broad arc from south-central Saskatchewan northwestward to its northern apex in central Alberta and then south along the east-facing slopes of the Alberta foothills. For the most part, the landscapes are hummocky glacial till plains characterized by short, steep slopes and numerous undrained depressions (sloughs) although along the foothills where the landscapes are more strongly influenced by the underlying bedrock, they tend to be more rolling with longer slopes and fewer depressions. Relatively level loamy, glaciolacustrine sediments and some coarse-textured sandy fluvial materials are found along the North Saskatchewan River valley. The bulk of the agricultural soils are loam to clay loam in texture and classified as Udic Ustolls (Black Chernozems) (Padbury and Acton, 1994).
Ecologically, this region represents a transition between the grassland environments to the south and the boreal forests to the north and is commonly referred to as the aspen parkland. As the name implies, it is characterized in its native state by a mosaic of aspen groves and fescue grasslands, and although the region is now largely cultivated, aspen groves are still found on many of the lower and north-facing slopes. Native fescue grasslands are rare (Acton et al., 1998).
About 80% of the area is arable, with cereals accounting for about half of the cropland. Over the past decade or so, there has been a significant increase in oilseed, forage, and specialty crops and a corresponding decline in summer fallow to the point where <10% of the cropland lies idle each year. Today, about 20% or the cropland is planted to oilseeds, mainly canola, and 10% is in perennial forage while specialty crops such as pea account for about 5% (Table 2).
Due to its relatively cool, moist climate and fertile black soils, this agroecoregion comprises some of the more productive agricultural land in the northern Great Plains, not only sustaining consistently high yields, but also supporting a variety of cereal, oilseed, forage, and specialty crops grown in extended diversified rotations. Compared with the bulk of the northern Great Plains, the generally favorable moisture conditions and cool temperatures, particularly from late June through early August, are particularly well suited to canola, forages, and specialty crops such as pea. While soil moisture is often limiting at some time during the growing season, on average, loam- and clay loam–textured soils are considered the most productive, particularly for crops like canola that are sensitive to excess moisture.
Agroecoregion 11
This agroecoregion comprises a relatively narrow band to the south of the aspen parkland, extending from northern North Dakota northwestward through Saskatchewan into Alberta and then southward to the Montana border. Often referred to as the moist mixed grassland, this area marks the northern extension of open grassland in the northern Great Plains and is closely correlated with semiarid moisture conditions and dark brown soils. Small aspen groves are found around many depressions and are a characteristic feature of the landscape, particularly compared with the drier mixed grassland to the south, which is largely treeless.
Most landscapes are glacial till, characterized by short, steep slopes and numerous undrained depressions or sloughs although several large glacial lake plains also occur (Acton et al., 1990). The bulk of the soils are loamy textured Typic Ustolls (Dark Brown Chernozems), which are intermediate in organic matter between the brown soils of drier mixed grassland and the black soils of the more humid aspen parkland. The clayey lacustrine sediments are characterized by Cryerts (Vertisols). Agronomically, the clayey-textured soils, because of their high moisture-holding capacity, have long been regarded as the most productive in the region. But with the trend toward longer rotations and stubble cropping, even the loam- and clay loam–textured soils have sufficient capacity in most years to store all precipitation received from harvest through the following spring, and thus are nearly as productive as the clays under those conditions.
Approximately 90% of the area is farmland, and most of it is cropped annually. Conditions are slightly drier than in the aspen parkland (Agroecoregion 10); consequently, yields are lower and crop diversity is less. Cereals are the dominant crop, with hard red spring wheat and, to a lesser extent, barley and durum wheat (T. durum Desf.) accounting for about half of the seeded area. Over the past 15 yr or so, there has been a significant increase in the production of oilseeds, particularly canola, along with pulse crops such as lentil (Lens culinaris Medikus) and pea while the practice of summer fallow, which had been widely used for weed control and in particular to store soil moisture, has been reduced almost by half to about 20% of cropland (Table 2). There has also been a significant increase in the use of reduced-tillage technologies to the point where almost half of the area is currently under some sort of reduced-tillage regime and about 20% is under direct seeding or zero-tillage (Padbury and Stushnoff, 2000).
Agroecoregion 12
This agroecoregion, located in southwestern Saskatchewan, southeastern Alberta, and northern Montana, is significantly drier than adjoining regions to the north and east, as evidenced by the absence of native trees and the scarcity of wetlands. The diverse landscapes include level glacial lake plains, dune-covered sandhill areas, the hilly Missouri Coteau, and the rolling expanses of native grassland and intermittent badlands in eastern Alberta and along the Saskatchewan–Montana border.
The bulk of the soils are Aridic Ustolls (Brown Chernozems), with Cryerts (Vertisols) characterizing the clayey glacial lake sediments. Because of their high soil moisture–holding capacity, the clays are particularly well adapted to a 2-yr crop–fallow rotation and have long been considered the most productive soils in the region. Large tracts of nonarable salt-affected soils are common in eastern Alberta. South of the border, most of the soils (Ustolls and Ustepts, frigid) are deep, well drained, and formed in loamy glacial till. Some have compact subsoil and, thus, a relatively low soil volume for plant roots. These gently undulating to rolling till plains include areas of kettle holes, kames, and moraines. Strongly rolling and very steep slopes are commonly associated with major stream valleys (Acton et al., 1998).
Over 85% of the area is farmland, but <60% is cropped annually. Cereals account for about half of the seeded area, with hard red spring wheat and durum wheat being the most common crops (Table 2). The production of oilseeds, mustard (Br. hirta), and canary seed (Phalaris canariensis L.), along with pulse crops such as lentil and more recently chickpea (Cicer arietinum L.), have increased significantly in recent years but still account for only about 10% of the cultivated area. Forage crops are grown mainly on marginally arable lands and account for about 5% of the cultivated land (Dumanski et al., 1994). The trend toward less tillage is similar to that in other parts of the northern Great Plains, with about half of the area being under a reduced-tillage regime and about 25% under direct seeding. The degree to which reduced tillage has been accompanied by longer rotations, however, has been significantly less compared with areas where moisture conditions are more favorable, and although the area of summer fallow has declined significantly, about one-third of cropland still lies idle each year.
Agroecoregion 13
This agroecoregion is characterized by a mix of forest and farmland, marking both the southern advance of the closed boreal forest and, with the exception of the Peace River country in northwestern Alberta, the northern limit of arable agriculture in the northern Great Plains. The forests occur mainly at the higher elevations where the landscapes are typically hummocky with moderate to high local relief and where external drainage is well developed. The soils there are mainly Typic Hapludalfs (Gray Luvisols) developed on loamy glacial till deposits and Eutrochrepts (Brunisols) found on the sandy glaciofluvial sediments. Agriculture, on the other hand, is confined mainly to the more fertile Mollic Hapludalfs (Dark Gray Luvisols) and Typic Hapludolls (Black and Dark Gray Chernozems) that occur at the lower elevations. Here the landscapes are typically level to gently undulating, surface drainage is poorly developed, and a high ground water table often influences the soils.
Similar to the aspen parkland to the south, this area is considered transitional between grassland and forest environments. And while the area was entirely under forest before cultivation during the early part of 20th century, the presence of soils having high levels of organic matter suggests that, historically, grasslands have been a major part of the environment here. The occurrence of Histosols (Organic) or peatland soils in many of the poorly drained depressional areas also reflects the long-term influence of a relatively cool, moist climate, particularly when compared with the slightly warmer and drier aspen parkland where few, if any, peatlands are found.
In contrast to the rest of the northern Great Plains where inadequate moisture is generally the factor most limiting crop production, a lack of heat is the main limiting factor here. Not only does a short growing season restrict the number of crops that can be grown, but the relatively cool, moist conditions often delay seeding or harvest operations, leading to reduced yields and lower crop quality. Nonetheless, the combination of adequate moisture and generally fertile soils make at least parts of the area well suited to forages as well as to short-season feed grains (oat and barley) and early maturing varieties of canola.
About half of the area is cultivated, and slightly less than half of that is seeded annually to cereals, most notably barley. Because of the short growing season, wheat is not the dominant cereal here as it is throughout the rest of the northern Great Plains. Over the past 20 yr or so, there has been a significant increase in the production of oilseed (canola), pulse (pea), and forage crops and a corresponding decrease in summer fallow, which has declined from about 25% of the cultivated land in the early 1980s to <10% today. Oilseeds, mainly canola, presently account for about 15% of the arable land, and specialty crops such as pea are grown on about 5%. The area planted to these crops varies year to year depending on market conditions. On the other hand, forage crops have steadily increased over the past few decades to the point where they now account for about 25% of the cultivated land, a much higher proportion than elsewhere in the northern Great Plains. Moreover, because they are particularly well adapted to the relatively cool, moist climate and, in the case of legumes, to the generally N-deficient soils, the potential for increased forage production is high, including expansion into the forested areas where soil and landscape conditions permit.
Agroecoregion 14
This agroecoregion is comprised of the level to gently undulating lands associated with the Peace River and its major tributaries in northwestern Alberta and adjacent British Columbia. In general, the area slopes gradually northeastwardly from the foothills of British Columbia to the Slave Lowland in Alberta. Clayey lacustrine deposits found in large glacial lake basins are the predominant parent material while fine-textured glacial tills and sandy glaciofluvial deposits are found around the margins of the basins.
Typic Hapludalfs (Gray Luvisols) are the predominant soils, especially at the margins of the glacial lake basins. Toward the center of the basins, the abundant understory vegetation coupled with slightly restricted drainage have resulted in the formation of Mollic Hapludalfs (Dark Gray Luvisols) and Typic Natrudalfs (Solods), with some Typic Hapludolls (Chernozemic) in the Alberta portion of the area.
This agroecoregion is classified as having a subhumid, low boreal ecoclimate, but because of its low altitude (300–700 masl) and proximity to the Rocky Mountains, it has a significantly milder climate than much of the surrounding area. The mean annual temperature is 0.50°C while the mean summer temperature is 13°C. The mean annual precipitation ranges from 350 to 600 mm.
The native vegetation forms part of the extensive deciduous forest belt, which extends as far eastward as Manitoba. The predominant vegetation is a closed cover of trembling aspen with secondary balsam poplar (Po. balsamifera L.) and an understory of mixed herbs and tall shrubs. White spruce [Picea glauca (Moench) Voss] and balsam fir [Abies balsamea (L.) Miller] are the climax species. There are some areas of more open parkland vegetation associated with a warmer climate and soils with darker surface horizons.
About 45% of the area is farmland, with annual small grains and forages dominating. Of the 25% of the farmland that is cropped annually, cereals occupy slightly more than 40% of the area and noncereals about 45 to 50%. Fallow occupies most of the remaining 10%. Hard red spring wheat is the dominant cereal at 25% of the cropland. Barley (12%) and oat (5%) constitute the other main cereals. Canola (22%) and forage (22%) are the key noncereals, with specialty crops such as pea (1.7%) and flax (0.1%) being a minor portion. There is a significant trend toward reduced tillage, with about 20% of the cropland being direct-seeded each year.
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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Toward that end, 14 agroecoregions within the northern Great Plains have been identified. Because climate acts as the primary control for ecosystem distribution, the agroecoregions, in essence, represent broad climatic zones. Specific boundaries on the map, however, are often derived indirectly using soil or vegetation information that reflects long-term climatic influence. It should be emphasized also that agroecoregions represent the upper level of a hierarchical ecological land classification. And while they are deemed appropriate for extrapolation of agronomic information at broad regional scales, a more detailed and sophisticated characterization of the soils, climate, and landscape is often required to answer questions about adaptation of specific crops on individual parcels of land. The climatic variation within agroecoregions (Table 1), for example, illustrates the need to intensify the characterization as more detailed geospatial data become available.
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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TOPABSTRACTINTRODUCTIONGENERAL DESCRIPTION OF THE...NOTESAGROECOSYSTEMS IN RELATION TO...AGROECOREGIONS OF THE NORTHERN...AGROECOSYSTEM DESCRIPTIONSSUMMARYREFERENCES |
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