Upgrade of soil survey information for Oxford County
Environmental concerns have become a major issue for the agricultural industry in the 1990's. In particular, southwestern Ontario has been a focus of concern as a result of agreements under the International Joint Commission (IJC) to reduce phosphorus delivery from the Lake Erie Basin. The Lake Erie Basin is also one of the most intensively farmed areas in Ontario with major specialty crop, cash crop and livestock industries. The Research Sub-program of the Canada-Ontario Green Plan is designed to encourage and assist farmers with the implementation of environmentally sustainable agriculture. To attain this overall goal, seven project areas were identified. This study falls under Project G - Monitoring Research Program - State of the Resources. The purpose of this Monitoring Research Program is to help farmers preserve land and protect the environment. The purpose of this study is to characterize the current state of the agricultural resources, identify areas where the resource is at risk and to provide a snap shot of their status for public information. An upgraded provincial soil data base is available for much of the Lake Erie Basin. This information is essential for the protection and designation of agricultural lands in Official Plans and also forms the basis for delivery of programs dealing with environmental impact assessments and sustainable agriculture. A major gap in the data base for this area is Oxford County. The existing soil map for Oxford County was upgraded so that it was compatible with adjacent county/regional municipality information. The selection of the Oxford County area is consistent with the objectives set out in the Green Plan program in terms of the scope, location, area of study and the study emphasis. The upgrade was undertaken according to present standards outlined by the Ontario Centre for Soil Resource Evaluation (OCSRE). The study focused on slope information generation, soil reliability checking and development of information and maps in electronic format. The soil polygons produced during the original Oxford County soil survey were used. The digitally generated slope polygons were then overlain over the original soil map. To generate the slope information for Oxford County, a Geographic Information System (GIS) was used to produce a digital terrain model. A triangulated irregular network (TIN) with a set of adjacent non-overlapping triangles was used to perform the digital terrain modelling. These nonoverlapping triangles were computed from digital contour lines and spot elevations of the 110 Ontario Base Maps (OBM's) covering Oxford County. Because a TIN identifies and stores information about the relationships among the points (contour lines and spot elevations), how the points define triangles, and triangle adjacency, TINs produce accurate terrain models for analyses. A stratified, random transect method was used for field verification purposes. This sampling procedure was used to verify slope mapping and provide an estimate of soil reliability for each soil polygon. The information compiled facilitated the production of an upgraded 1:50,000 map in electronic format. The field verification of the digitally generated slope information showed that the GIS generated slope information was accurate. Sixty-five percent of the slopes verified in the field agreed with the digitally slope class polygons, while an additional 30 percent were within one slope class. The original soil information was also fairly accurate. Field studies showed that 56 percent of the soils were identified as mapped, while 74 percent were found within the correct soil catena. Most of the discrepancies were due to differences in drainage class. In counties where no slope information is available, this method of digitally generating slope information can be used to upgrade soil maps to include slope information.