Land Suitability Rating System for Agricultural Crops (LSRS_Can)

This report outlines a procedure for rating the suitability of land for production of spring-seeded small grains (and hardy oilseeds) in Canada.

The system is interpretive and based on limitations for crop production. The framework of the system is suitable for all crops but specific rating factors are developed, initially, for only spring-seeded small grains (wheat, barley, oats), crops which can be grown in all the agricultural regions of Canada.

The system recognizes three major components that determine the suitability of land for crops: climate, soils and landscape. Each component is rated separately and assigned a value between 0 and 100. The final land suitability rating is based on the most limiting of the three, not on the accumulated total.

Climatic limitations are assessed using two indices, a ‘moisture factor’ and a ‘temperature factor’.

The Moisture Factor rating is determined by calculating the difference between precipitation and potential evapotranspiration for the May to August period. The difference is used for calculating point deductions from the maximum rating.

The Temperature Factor rating is based on a calculation of ‘effective growing degree days’, which include length of season, degree days and day length. Growing degree days are accumulated from the approximate date of seeding up to the average date of the first frost, and are adjusted to recognize the effect of longer day length in northern Canada.

Modifying factors affecting the ratings are  excess spring moisture, excess fall moisture, and early (fall) frost. The excess spring moisture factor recognizes effect of excess spring moisture in delaying seeding operations and  effectively shortening the growing season. The excess fall moisture factor reflects the adverse effect of excess moisture during harvesting. The fall frost factor accounts for the occurrence of frost prior to the regional average.

The rating for mineral soils is assigned using four characteristics, (i) the moisture supplying ability, (ii) the surface factors, (iii) subsurface factors, and (iv) drainage.

Moisture supplying ability is evaluated through measurement of the available waterholding capacity, or, in its absence, soil texture. Adjustments are made for subsurface texture and water table.Surface factors include structure and consistence, organic matter content, depth of topsoil, pH, salinity, sodicity, organic surface . Subsurface factors include structure and consistence, presence of a distinct change in geological material, pH, salinity and sodicity. Drainage is evaluated through the factors depth of the water tableduring the critical spring period, the saturated hydraulic conductivity of the most drainga-limiting layer, and the general climate of the region.

In all cases soil conditions are scored through percentage deductions from the maximum depending on the severity of the limitation. Special ratings were developed for organic soils.

The rating for landscape is based on limitations generally related to management, such as the ease of use of farm machinery, uniformity of growth and maturity of crops and the risk of losing topsoil by either erosion or cultivation. The basic landform rating depends on the rainfall erosivity region, modified by taking into consideration slope length, stoniness, wood content in organic soils, landscape pattern, and flooding.