What is soil survey?

Soil survey is an inventory of the properties of the soil (such as texture, internal drainage, parent material, depth to groundwater, topography, degree of erosion, stoniness, pH, and salinity) and their spatial distribution over a landscape. Soils are grouped into similar types and their boundaries are delineated on a map. Each soil type has a unique set of physical, chemical and mineralogical characteristics and has similar reactions to use and management. The information assembled in a soil survey can be used to predict or estimate the potentials and limitations of the soils’ behavior under different uses. As such, soil surveys can be used to plan the development of new lands or to evaluate the conversion of land to new uses. Soil surveys also provide insight into the kind and intensity of land management that will be needed. 

What are soil survey reports?

A soil survey describes the characteristics of the soils in a given area, classifies the soils according to a standard system of classification, plots the boundaries of the soils on a map, and makes predictions about the behavior of soils. The different uses of the soils and how the response of management affects them are considered in designing and carrying out the survey. The information collected in a soil survey helps in the development of land-use plans and evaluates and predicts the effects of land use on the environment (adapted from the USDA definition of “soil survey”).

Soil survey reports contain two parts. The first component is a soils map or series of maps at a particular scale with coding for soil types. Soil survey reports also include a supporting document that contains background information, how the soil survey was conducted, an explanation of interpretive criteria and a summary of the area occupied by various soil types.

Map Information Soil Polygon - an area (which can be of any shape) which contains essentially uniform soil type, according to the degree of scale used in the mapping.  In addition to the limitations of map scale, the boundaries of the soil map polygons imply there are abrupt changes in soil types within the landscape. In reality, however, soil varies continuously across the landscape. It must be recognized that, although the map lines imply abrupt changes, the soil grades from one type to the next and the lines on the map are only approximations of where these transitions occur. Map Units - symbols on soil survey maps that represent the type of soil(s) found within a particular polygon. A simple map unit designates a single soil series on a detailed soils map. A complex map unit includes as many as three soil series on a detailed map, or as many as two soil associations on a reconnaissance soil map. Other information on the soil phase, such as extent of erosion, slope gradient, stoniness and salinity, may be included within the map unit.

Figure 2.2  Derivation of map unit symbology

Why is map scale important?

Reconnaissance (general) soil surveys of Manitoba were started in 1926 as the first step in the development of a basic program of soil research, education, conservation and utilization for the province. (Scale is approximately 1:125,000, or 1/2 inch to 1 mile.) In recent years, many developments have occurred in agriculture that have created demand for soils information that is beyond the scope of detail provided in reconnaissance surveys, such as:

• research trials
• manure application and nutrient management
• precision farming
• soil productivity for production insurance ratings
• land use planning
• suitability for irrigation and drainage
• tax assessment
• watershed management

Figure 2.3  Current availability of detailed soils information for complete
rural municipalities of agro-Manitoba

Note:  There are several municipalities in other parts of Manitoba that have a portion of their area surveyed at a detailed level.  Many of these areas surround town sites and were conducted for the purpose of assessing soil suitability for sewage lagoons. Contact your local Manitoba Agriculture, Food and Rural Initiatives office for a complete list of current and on-going detailed soil survey activities.
 

The first large-scale, or detailed, soil survey in Manitoba was published in 1972 for the Portage la Prairie area at a scale of 1:20,000. Detailed soil surveys identify more of the variation in soil types across smaller landscapes (Figure 2.4).  Detailed soil survey maps are much more accurate and reliable for making decisions at the farm-level (Table 2.1).  Field inspection sites for a 1:20,000 map scale (3.2 inches to 1 mile) requires 25-30 inspection sites per section of land (Figure 2.5). Semi-detailed maps at 1:50,000 scale, or 1.5 inches to 1 mile, require 16 inspections per section. A two-person crew usually maps 1 section per day. Mapping costs are approximately $3.00-7.50/acre, but this is a one-time cost, as most soil properties remain unchanged over a lifetime. 

Table 2.1  Intended uses for maps according to scale

Figure 2.4  Comparison of soils information on same land parcel at detailed (1:20 000) scale (left) versus reconnaissance (1:126 620) scale (right)

Figure 2.5  Typical soil sampling and inspection pattern for
a detailed soil survey
 

Why are detailed soil survey reports required for in-field assessments?

Soil survey maps are not without limitations. Although the map may say that a discrete area of land contains a certain soil type, it must be understood that the reliability of that information is a function of the map scale. All soil delineations (called polygons) contain small areas of dissimilar soils that are not identified (called inclusions). The smaller the scale of the map (or the more general the map), the more frequently this occurs.  Small-scale, reconnaissance or general soil surveys give only a broad picture of the dominant types and distribution of soils that occur over relatively large areas. The landscape may actually include fairly significant areas of different soils that are not identified on the map. As such, reconnaissance soil surveys are best suited to making general comparisons of soil capabilities and limitations on a regional, national or even worldwide scale. They are not reliable for making on-farm decisions as they lack the detail necessary to describe the variation in the soil types on the farm (Table 2.1).

Recent translation of soils information in reconnaissance areas into digital maps and an interpretive data base (eg. as agriculture capability) looks like detailed soil series information. However, this data has not been verified by field inspections to the same extent as detailed soil surveys. As a result, these maps are not as reliable at the farm level as detailed soil survey information. This data should only be used for general soils information purposes or coupled with detailed soils data from field visits; it should not be relied on solely for on-farm decisions.
 

Options for data collection when detailed soil survey information is unavailable

When detailed soil survey data is needed but unavailable, on-site investigations are necessary. On-farm soil survey can be designed for a specific purpose or general purpose. A specific, or single purpose survey may be appropriate when there is only one, well-defined objective (such as siting a livestock operation).  In this instance, only the information required to meet the single objective may need to be collected. The major advantage to a single purpose survey is decreased cost. A general-purpose survey, on the other hand, contains a wider range of information.  Although more information is more costly to collect, the general-purpose soil survey may have more value over the long-term as it can be interpreted in a variety of ways and can be reused for many purposes.

As detailed soils information is not available in all parts of Manitoba, some information about the soil types present in the landscape can be gleaned from aerial photos, yield maps, infrared maps, etc. Coupled with the landowners’ knowledge of the area, several interpretations can be made:

• Scale and acreage determination
• Identify major features such as roads, rail lines and yard sites
• Identify soil features such as knolls, depressions and saline areas
• Using personal experience, yield maps or strip trial data, locate crop features
  (i.e. Where are best yields, poorest yields usually found?)
• What management decisions can be made?  Or is more information needed? 
  Is a field investigation warranted?

The reliability of the field data and its interpretation is largely dependent on the experience and ability of the surveyor. Data collection should always follow standardized procedures and should only be carried out by those who have received training in soil survey. 

An example of soil survey interpretation is the evaluation of a given land base for manure application. The type of soil and its associated characteristics determine the crops that can be grown, their yield potentials, the quantities of nutrients that are needed and the field practices that will be necessary to maintain optimum soil conditions for plant growth. As well, soil data on permeability (the rate at which water moves through a soil), depth to groundwater, flooding, slope gradient, soil texture and depth to bedrock can be useful in determining the risk of groundwater contamination due to leaching or surface water contamination due to runoff and erosion. 
 

Interpretive maps

The following conceptual model depicts the information required to make on-farm land use and land management decisions that are objective, consistent and technically sound. 

Agriculture capability for Manitoba

Agriculture capability is a 7-class rating of mineral soils based on the severity of limitations for dryland farming, which implies a risk to regional production capacity when soils are farmed and the way these soils respond to management. This system does not rate the soil’s productivity, but rather its capability to sustain agricultural crops based on limitations due to soil properties, topography and climate on a soil polygon basis. Class 1 soils have no limitations, whereas class 7 soils have such severe limitations that they are not suitable for agricultural purposes. In general, it takes about 2 acres (0.8 hectares) of class 4 land to equal production from 1 acre (0.4 hectares) of prime (class 1) land. (From Land:  The Threatened Resource).

• Class 1, 2 and 3 soils are capable of sustained production of common field crops
• Class 4 soils are marginal for sustained arable agriculture and should be in permanent forage production
• Class 5 soils are suitable only for improved permanent pasture
• Class 6 soils are capable only for native pasture use
• Class 7 soils are incapable of use for arable agriculture or permanent pasture

Agriculture capability subclasses identify the soil properties or landscape conditions that may limit use. A capital letter immediately following the class number identifies the limitation (eg. 2W, 3N, etc.). 

Subclasses:

C – adverse climate (outside the boundaries of agro-Manitoba)
D – dense soils (undesirable soil structure/low permeability)
E – erosion damage
I – inundation (flooding) by streams and lakes
M – moisture (droughtiness) or low water holding capacity
N – salinity
P – stoniness
R – consolidated bedrock
T – topography (slopes)
W – excess water other than flooding (inadequate soil drainage or high water table)
X – two or more minor limitations
 

How does agriculture capability compare to the crop insurance Soil Productivity Index ratings?

Crop insurance coverage is based on a 10-category classification system for cultivated land based on soil productivity as determined by crop yields. The ratings are from A to J with A being the most productive and J the least. Each quarter section receives a single rating and the ratings are calculated based on moving average cropping data, temperature, precipitation and soil factors such as organic matter, sub-surface material, texture, drainage, depth of topsoil, topography, salinity and erosion.  Ratings are modified to account for local risk factors such as frequency of drought, frost, flooding and other natural hazards.  As a result, a quarter section with several soil polygons will have several agriculture capability ratings, but will always have one soil productivity index rating.
 

Irrigation suitability 

Irrigation suitability is a general suitability rating for irrigated crop production. This classification system considers soil and landscape characteristics such as texture, drainage, depth to water table, salinity, geological uniformity, topography and stoniness and ranks them in terms of their sustained quality due to long term management under irrigation. It does not consider factors such as water application, water availability, water quality or economics of this type of land use.  Classes are excellent, good, fair and poor.
 

Soil suitability for irrigated potato production

Deep, well-drained, sandy loam to loam soils exhibit favourable properties for the production of high quality potatoes. This rating is a 5-class evaluation of soil properties and landscape features that are important for irrigated production of potatoes for processing, with Class 1 soils most suitable and Class 5 soils least desirable for this use. Texture, drainage, salinity, sodicity, topography and stoniness are considered.
 

Other assessment ratings

Detailed soil survey reports include assessment criteria for several other non-agricultural uses that may be of value to engineers, land use planners and the general public. These suitability ratings include soil assessments for:

• source of top soil
• source of sand and gravel
• source of road fill
• permanent buildings with basements
• local roads and streets
• sanitary trench
• landfill area
• cover material
• sewage lagoon
• septic field
• playground
• picnic area
• camp area
• path and trails
• permanent buildings without basements

Table 2.2  Dryland agriculture capability guidelines for Manitoba

Based on the Canada Land Inventory Soil Capability Classification for Agriculture (1965, Rev. 2001), with modifications made for soil application at larger mapping scales.

Click table below to enlarge

1. Smith, R.E., H. Veldhuis, G.F. Mills, R.G. Eilers, W.R. Fraser, M. Santry, 1996. Terrestrial Ecoregions and Ecodistricts of Manitoba, An Ecological Stratification of Manitoba’s Natural Landscapes. Agriculture and Agri-Food Canada, Research Branch, Brandon Research Centre, Manitoba Land Resource Unit, Winnipeg, MB. Report and Provincial Map at scale of 1:1.5m.
2. With the exception of class 2, ratings as indicated are based on the assumption of a single parent material, using the most readily drained representative of each textural class.  Prevailing climatic conditions within the Ecodistrict, soil drainage and stratification will affect the moisture limitation accordingly.
3. Topographic classes are based on the most limiting slope covering a significant portion of an area of complex, variable slopes.  Map units with long, unidirectional slopes may be considered equivalent, or one class worse due to an increased erosion hazard.
4. Extremely calcareous loamy till soils with a high bulk density (>1.7 g/cm³) are rated 3D.
5. Soil Salinity is reported in DeciSiemens/metre (dS/m).  Soil will be classed according the the most saline depth.  For example, if a soil is non-saline from 0-60 cm but moderately saline from 60-120 cm, the soil will be classed as moderately saline (3N).
6. Strongly saline (u) soils are rated 5N with the exception of poorly and very poorly drained soils, which are rated 6NW.
7. Inundation may be listed as a secondary subclass for some fluvial soils.  In this case, inundation is not class determining, but may become a limitation if the soil is otherwise improved.
8. Extremely calcareous loamy till soils with a high bulk density (>1.7 g/cm³) and stony 3 are rated 4DP (4RP if depth to bedrock is 50 - 100 cm).
9. Stony 4 soils will be rated 4P unless their primary physical composition is sandy skeletal or their parent material is till.  In either or both of these cases, the soil will be rated 5P.
10. If erosion is moderate, a subclass of E is assigned as a secondary limitation, but the basic rating is not lowered. If erosion is severe, the basic soil rating is downgraded by one class, and E becomes the primary limitation. For example, if a soil has a basic rating of 4T, the presence of moderate erosion will result in a rating of 4TE. If erosion is severe, the rating will be lowered to 5ET. Erosion will be the sole limitation only if the basic rating has a subclass of X. For example, a soil with a rating of 3X will be assigned a rating of 3E if moderate erosion is present.
11. The rating is not lowered from class 6 based on erosion. A rating of 6TE indicates a soil with g topography and either moderate or severe erosion.
     

Table 2.3  Landuse data based on satellite imagery from 1993-1994

Table 2.4  Agriculture capability data based on 1:1,000,000 Canada Land Inventory map information

Provincial soil concept

Soil is one of our most valuable natural resources. To ensure that we do not take this resource for granted, soils need to be protected and managed in a sustainable manner. Designation and proclamation of a provincial soil is one way to increase public awareness and create a greater appreciation for soils.

The concept of provincial soils is practiced to a limited extent in Canada and universally in the United States. As of 2000, every state in the United States (including Guam, Puerto Rico and the US Virgin Islands) has designated a state soil. Of these, 13 have received official proclamation by their state legislature (USDA-NRCS, 2000 State Soil Planning Guide).

Table 2.5  Current status of provincial soils in Canada

Newdale Series (NDL)

The Newdale series is characterized by an Orthic Black Chernozem solum on moderately to strongly calcareous, loamy (L, CL) morainal till of limestone, granitic and shale origin. These soils are moderately well to well-drained and occur in mid to upper slope positions of undulating to hummocky landscapes. Surface runoff is moderate to moderately rapid; permeability is moderately slow. Most of these soils are presently cultivated; they have formed under intermixed aspen grove and grassland vegetation.

The Newdale solum has a very dark gray Ah horizon, commonly 10-inches (25-centimetres) thick and ranging from 6 to 14 inches (15 to 35 centimetres), a dark brown Bm horizon, 4- to 12-inches (10- to 30-centmetres) thick, and a transitional BC horizon, 1- to 6-inches (3- to 15-centimetres) thick. A lime carbonate horizon, 4- to 6-inches (10- to 15-centimetres) thick is often present in shallower soils but is not evident in deeper profiles. Its solum depth averages 23 inches (58 centimetres) and ranges from 10 to 35 inches (25 to 90 centimetres).

Table 2.6  Newdale soil analysis

| Understanding the Soil Landscapes in Manitoba | Using Soil Survey Information | Water Use and Moisture Management | Nutrient Management | Soil Salinity | Drainage | Soil Erosion | Tillage, Organic Matter and Crop Residue Management | Soil Compaction | Soils Information for Planning Purposes | Other Applications of Soils Information | Summary | References | Appendices|