PRODUCTIVITY INDEX MODEL COMPARISON FOR SELECTED SOILS IN NORTH CENTRAL UNITED-STATES

The productivity index (PI) model is a derived measure of soil productivity. The basic assumption of the PI model is that crop yield is a function of root development, which in turn is controlled by the soil environment. The PI model in conjunction with estimated soil property values contained in the SCS Soil Interpretation Record (SIR) data base are the basis of formulating predictions of long-term productivity changes by soil erosion in soil series, and has been used to target conservation programs within regional areas. Comparisons were made of PI values obtained using SIR estimations for selected soil series in the North Central Region of the U.S. PI values were determined from field data measured by erosion class for these soils at specific sites to determine if the PI model could be used as a method to predict soil reproductivity as modified by erosion. Results from these comparisons show that the PI model can be used to efficiently to characterize soil productivity at specific sites if accurate field data are available. However, using the midpoint of the range shown in the SIR data base may not be adequate to describe specific sites. The SIR data base can be useful in providing generalized comparisons between soil series, but may not account for site specific variations within a soil series.