Attempts to rate the suitability of land for food production probably began with the dawn of arable agriculture (Simonson, 1968). From the early days of soil survey in Canada, ratings were made of the agricultural potentials of mapped areas (McKeague and Stobbe, 1978). The first national land inventory in Canada, the Canada Land Inventory (CLI) (ARDA, 1965), was based largely on soil survey information, and the initial capability rating was for common field crops. Over the years several agencies modified the CLI for a variety of purposes. In some cases, new systems of land capability rating were developed. The use of different systems led to confusion and conflict. Concern about this was expressed at the meeting of the Expert Committee on Soil Survey in 1986, and the Land Resource Research Centre responded in 1987 with the formation of an Agronomic Interpretations Working Group, with representation from all regions of Canada.
The Working Group examined a number of systems used to rate land for the production of agricultural crops. They included the systems used in British Columbia (Kenk and Cotic, 1983), Alberta (Alberta Soils Advisory Committee, 1987) and the Ottawa area (Marshall et al., 1979) as well as Ontario (Brokx and Presant, 1986), Quebec (Mailloux et al., 1964) and the Atlantic Region (Atlantic Advisory Committee, 1988). Several climatic stratifications were also reviewed (Chapman and Brown, 1966; FAO, 1976; Williams, 1983). Conclusions from the initial assessment were:
a) the inadequate consideration of climate,
b) the omission of organic soils from the system,
c) the inadequate documentation of criteria, and
d) the subjectivity of the rating process.
It was agreed that:
With the above direction, the Working Group proceeded with exploratory work in 1988, development of a climatic framework for the system in 1989, preparation of a draft report in 1990, and testing and modification of the system in 1991. The result was a "working document published in 1992 which was circulated to Land Resource Units across the country for exposure to local clients and further testing. Feedback from this phase was used for further modification and clarification to produce the present document. At the same time a computer program, written in dBASE, was developed for automated calculations.
This document should be viewed both as a general procedure for assessing land suitability for crop production and as a specific system for rating land suitability for spring-seeded small grains. The spring-seeded small grains, which include wheat, barley and oats, were selected to develop the procedure and format because they can be grown throughout the agriculture area of Canada. The system should work equally well for hardy oilseeds such as canola and flax which have similar land resource requirements. As the CLI ratings were designed for common field crops suited to the area (ARDA, 1965), the two systems should be roughly similar. The system described herein includes most of the attributes of an optimum approach to soil productivity rating as outlined by Huddleston (1984).
The principal objectives of the working group were to clarify and specify the input parameters so that the rating could be documented and automated, to develop a uniform national approach and to provide for expansion of the rating to a variety of crops. As such, this report does not present new information so much as to reorganize, document and specify our present approaches and knowledge. In so doing, it also identifies areas of weakness and directs testing and research for improvements. It is an attempt to improve the quality and particularly the uniformity of land suitability rating in Canada.