Manitoba Agricultural Services Corporation

 

Summary of MASC Soil Productivity Indices

Beginning in the late 1930s the Manitoba Soil Survey started to group and classify soils based on morphological features. To date, most of Manitoba’s agricultural land has been mapped and classified in the form of soil survey reports, which provides the basis for MASC’s Productivity Indices.

In order to assess the productivity of these lands, a joint project was undertaken by the Manitoba Department of Agriculture, the Department of Soil Science at the University of Manitoba and the Manitoba Soil Survey.

Major soil types in the province (benchmark soils) were selected and the long term (35 years) average wheat, oats and barley yields were obtained for each soil from the Dominion Bureau of Statistics, the Sandford-Evans Statistical Service and the Veterans’ Land Act Administration.

The benchmark soils were then placed in one of ten classes (A – J) with the soils having the highest yields being classed as A and the lowest yielding soils being rated as J. The characteristics of all other soils mapped by the Soil Survey were then studied and compared to these benchmark soils and were placed in appropriate productivity classes.

Factors in Rating Soil Productivity

Soil productivity is dependent upon the interaction of certain soil factors with one another, and with climate:

• Climate Factors: include temperature (length of growing season, frost hazards, heat units) and moisture (precipitation totals and distribution as well as evaporation rates).
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• Soil Factors:
  • Soil Texture - important because of effect on moisture retention. Higher ratings were given to medium textured soils such as loams and clay loams. Lower ratings are given to heavy clays (poor internal drainage) and sandy soil (prone to erosion, lower water holding capacity and lower fertility due to leaching).
  • Organic Matter - important due to its relationship with fertility, tilth and water retention.
  • Drainage Characteristics - natural internal soils drainage is of more importance than surface drainage.
  • Topsoil Depth - important because it determines the rooting zone and is related to the total amount of organic matter and available plant nutrients in the soil.
  • Salinity - when the soluble salt concentration is high soil productivity is greatly reduced.
  • Soil Erosion - the amount of topsoil removed is considered when rating a soil. Usually the potential for soil erosion is related to texture and topography of the land.
  • Topography - contributes to the degree of erosion and localized drainage problems.
  • Stoniness - of minor importance unless it is sever enough to limit cultivation and land use.
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• Risk Area: A Risk Area is defined as an area of common production risk (see Risk Area Map). The criteria used for delineating risk areas was to place areas with similar soils and/or climate into a common group. It should be noted that a C soil in Risk Area 12 may not have the same productivity as a C soil in Risk Area 6 due to climatic differences.

Soil Productivity Index and Average Yield

Generally, the relationship between soil productivity index and average yields is quite good. As the soil productivity rating decreases, the average yield also decreases.

Soil Productivity Index and Individual Productivity Index

The MASC soil productivity index is important for determining the individual productivity index (IPI) used to establish the probable yield (yield expected for each crop) that is used for coverage determination based on each individual's yield history.

The IPI calculation uses the producer's yield compared to the other producers growing the same crop in the same soil and risk area. The yield comparison determines the results of an annual index.

Note: Where a lack of data occurs for an area (ie. fewer than three producers, or insufficient data for a specific crop type), a larger area is used for comparison.

Example: A producer gets 40 bu/acre on D05 soil, and the average bu/acre on D05 soil is 38. The producer's resulting index is: 40 / 38 = 1.05.

The annual indices are averaged over a 10-year period to reult in an IPI for the current crop year. For additional information about the IPI, please review the Individual Productivity Index factsheet.

Re-Inspecting Soil Classifications

If you have fields you feel that MASC have classified incorrectly, MASC can perform a reinspection. Your local Insurance agent can walk you through a 'Soil Zone Reinspection Questionnaire' to determine if a reinspection is warranted.

If warranted, an MASC agrologist will come out and complete a field inspection. Field inspections are important, as an agronomic interpretation may be required beyond the information available from a soil survey map.