CM is an index of cost of the needed corrective measures. Finally, CL is an index of the extent to which the feasible corrective measures are not fully successful. It reflects costs for annual or periodic maintenance, for inconvenience or aggravation, or for substandard yield. Alternatively, qualitative ratings of soil potential may be employed. The soil has few limitations, or practices for overcoming the limitations are available at a reasonable cost.
Crop production is profitable and at least average for the area.
For a particular use, performance of the soil is satisfactory or as good as, or better than, local standards. The soil has a combination of properties intermediate between those qualifying for high potential and those qualifying for low potential. Production is somewhat below local standards, cost of corrective measures is high, or continuing limitations after measures have been installed detract from environmental quality or economic return. Crop production is substantially below the local average and is economically marginal or submarginal. A five-class system may be needed.