Predicting corn and soybean productivity for Illinois soils

Current corn and soybean productivity data is needed in Illinois for land-use planning, sustainable farm management, and accurate land appraisal. The out-of-date source of soil productivity data is Circular 1156 Soil Productivity in Illinois (Fehrenbacher et al., 1978, Soil productivity in Illinois.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 assure the availability of reliable 10-year average corn and soybean yield estimates 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 approach based on multiple regression was used to evaluate the relationship between 16 selected soil properties of 34 major soils and established 1970s (1967±1976) corn and soybean yields as published in Circular 1156. Statistical 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 coecients generated from multiple regression were further tested using the soil property values for the additional 165 soils identi®ed in nine 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 trend increases were added to the established (Circular 1156) and model predicted 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 selected counties. The 1990s crop yield estimates for the selected counties were weighted by extent of each soil type in the county and compared against 10-year county averages for the 1990s farmer reported Illinois Agricultural Statistics (IAS) corn and soybean yields. Predicted 1990s county crop yields were statistically similar to 0308-521X/00/$ see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII : S0308 -521X(00)00020 -2 Agricultural Systems 64 (2000) 151±170 www.elsevier.com/locate/agsy * Corresponding author. Tel.: +1-217-333-9639; fax: +1-217-224-3219. E-mail address: [email protected] (K.R. Olson). 1990s farmer reported (IAS) county crop yields. The proposed approach to updating corn and soybean yields worked well and should be useful in surrounding states or countries. # 2000 Elsevier Science Ltd. All rights reserved.