Predicting corn and soybean productivity for Illinois soils

Current corn and soybean productivity data is needed in Illinois for land-u se planning, sustainable farm management, and accurate land appraisal. The out-of-date source of soil productivity data is Circular 1156 Soil Producti vity in Illinois (Fehrenbacher et al., 1978, Soil productivity in Illinois. UIUC. College of Agriculture. COOP. EXT. SERV. Circular 1156). A new major analysis based on current Illinois farmer crop-yield data is needed to ass ure the availability of reliable 10-year average corn and soybean yield est imates by soils. The overall objective of this study was to update the corn and soybean yields which serve as a productivity index for Illinois soils since these two crops are grown on approximately 90% of the cropland. An ap proach based on multiple regression was used to evaluate the relationship b etween 16 selected soil properties of 34 major soils and established 1970s (1967-1976) corn and soybean yields as published in Circular 1156. Statisti cal models developed from major soils were tested internally by calculating the 10-year average corn and soybean yields for each of the 34 major soils . The coefficients generated from multiple regression were further tested u sing the soil property values for the additional 165 soils identified in ni ne counties representing the crop reporting districts and weather districts in Illinois. The 10-year average crop yield trends were determined for 66 counties in the northern region and for 36 counties in the southern region for the 20-year time period between 1976 and 1995. These 20-year yield tren d increases were added to the established (Circular 1156) and model predict ed 1970s crop yields to estimate 1990s (1986-1995) corn and soybean yields for the average management level for all 199 Illinois soil types in nine se lected counties. The 1990s crop yield estimates for the selected counties w ere weighted by extent of each soil type in the county and compared against 10-year county averages for the 1990s farmer reported Illinois Agricultura l Statistics (IAS) corn and soybean yields. Predicted 1990s county crop yie lds were statistically similar to 1990s fanner reported (IAS) county crop y ields, The proposed approach to updating corn and soybean yields worked wel l and should be useful in surrounding states or countries. (C) 2000 Elsevie r Science Ltd. All rights reserved.