Predicting crop yields and productivity indices for Illinois soils

An approach based on multiple regression was used to evaluate the relationship between 16 selected soil properties of base and benchmark soils and established 1970s crop yields as estimated in Circular 1156, Soil Productivity in Illinois. These crops included: corn, soybean, wheat, and forage for northern and southern soil regions in Illinois and oat in the northern region.; Statistical models developed from base and benchmark soils were tested by calculating the average crop yields for all the cropland soils in nine different counties representing the crop reporting districts in Illinois. The model predicted crop yields were compared to the published 1970s Circular 1156 average yield estimates for each crop, and to the published 1970s crop yields reported in Illinois Agricultural Statistics.; Comparing established (Circular 1156) crop yields with predicted 1970s crop yields, generated from soil property models from base and benchmark soils, predicted high R2 values of 0.90 for corn, 0.90 for soybean, 0.81 for wheat, 0.81 for oat, and 0.88 for hay. These crop yield models were tested with 167 supplementary soils from nine selected counties representing the crop reporting and weather districts for Illinois. The equations explained 50% of the yield variation for corn, 47% for soybean, 41% for wheat, 33% for oat, and 47% for hay. Outliers (greater than +/-2 SD) were identified for further analysis. The relationship between crop yields, versus time (years) were established using regression analysis. Crop yield trends and magnitude of change were estimated for 66 countries in the northern region and for 36 counties in the southern region for the time period between 1976 and 1995. The magnitude of crop yield change by region was added to the 1970s predicted and established yields to generate the 1990s predicted and established yields. These yields were compared against 10-yr averages for the 1990s as reported in IAS for the nine test counties. As in the 1970s comparisons, predicted yields were closer to reported IAS yields than those established in Circular 1156 and projected to 1990s. There were no significant differences between the nine county predicted 1990s yields and the IAS 1990s yields for corn, soybean, and wheat.