Development and use of soil productivity ratings in the United States

This paper provides historical documentation of major U.S. efforts to develop numerical ratings of soil productivity. Nearly all of these efforts stemmed from needs to compare different soils objectively for purposes of agricultural land use planning and the equalization of land values and tax assessments.Several approaches are described, including U.S.D.A. work following World War I, ratings based solely on crop yield data, Storie's (1933, 1937, 1976) multiplicative factor approaches and the variations that evolved from them, and “Soil property systems” that add, rather than multiply, effects of separate factors. Taken together, these various approaches highlight a large number of soil properties, weather conditions, and crop yield data that need to be considered to develop ratings of soil productivity. They illustrate a variety of techniques for evaluating the effects of soil properties quantitatively and for combining soil factor values into overall soil ratings. Each approach has certain advantages and limitations, and these are discussed throughout. The collective experiences with the development and use of productivity ratings cover a diversity of soil and climatic conditions throughout the United States.