USING SOIL PROPERTIES TO PREDICT WHEAT YIELDS ON ILLINOIS SOILS

Abstract

Updated crop yield estimates for different soil types are required to meet the needs of farmers, land appraisers, and governmental agencies of most states within the United States. The objective of this study was to update wheat [Triticum aestivum L.] yield estimates for all soil types in the state of Illinois under the average management level used by all Illinois farmers in the 1990s. A crop yield soil properties (CYSP) model was developed from established 1970s wheat estimates and soil properties. Correlation and multiple regression analysis was used to establish the relationships between 16 physical and chemical soil properties and wheat yields. Using step-wise multiple regression, a final CYSP model with six variables (% silt in A and E horizons, % organic matter in A and E horizons, cation exchange capacity, rooting depth, bulk density of the B horizon, and Na content) explained 78% of the variation in 1970s wheat yields of (R 2 = 0.78 [34 soils]). A 22-year yield trend was applied to the 1970s predicted and established wheat yields to estimate the 1990s yields under an average level of management used by all Illinois farmers. The 1990s wheat yields (model predicted plus trend) were compared with both established (Circular 1156) plus trend yields and with farmer-reported yields by Illinois Agricultural Statistics (IAS) Staff for 161 soils in nine test counties. Predicted 1990s test county wheat yields showed no statistical differences between the three data sources. The final 1990s wheat yield estimates for all Illinois soil types were the mean of the estimates from: (i) the established 1970s yields plus 22-year yield trend, (ii) the model predicted plus 22-year yield trend, and (iii) the 1990s farmer-reported yields. The proposed approach to updating wheat yields worked well in Illinois and should be useful in surrounding states and/or countries.