Soil Potential Ratings (SPR)

Soil potential ratings (SPR) are classes that indicate the relative quality of a soil for a particular use as compared with those of other soils in a given area. The following are considered in soil potential ratings: yield or performance level, the relative cost of applying modern technology to minimize the effects of any soil restrictions, and the adverse effects of continuing limitations, if any, on social, economic, or environmental values. The classes developed for SPR are based on a soil potential index (SPI) for each soil. SPI is a numerical rating of a soil’s relative suitability or quality for a specified crop or use. SPI can be expressed by the equation: SPI = P – (CM + CL) where P= index of performance or yield as a locally established standard, CM = index of costs of corrective measures to overcome or minimize the effects of soil limitations and CM = index of costs resulting from continuing limitations. The index values used are of a general nature and do not require a highly detailed economic analysis of costs and returns . The methods and criteria for developing soil potential ratings for a particular use are established specifically for a given area and may be different in other areas. The rating classes are defined in terms of the production or performance expected of a soil if feasible measures are taken to overcome its limitations and in terms of the cost of such measures and the magnitude of the limitations that remain after the measures have been applied. Whereas the production or performance of each soil is compared with standards that are established locally for each soil use, the class terms and definitions are applicable nationwide: very high, high, medium, low and very low potential.