Relationships Between Parameters of Combine Design and Soil Compaction

Modern combines do cause soil compaction due to excessive axle loads and resulting ground contact pressures, which can substantially reduce soil productivity: Researchers have documented crop yield reductions up to 60%. Field observations, consisting of soil bulk density, cone index, and moisture content measurements, indicated that combines with estimated front axle loads of 7-15 Mg and nominal ground pressures of 63-122 kPa did cause soil compaction. From manufacturers\u27 data on the largest combines of highest capacity, front axle loads were found to be as high as 18 Mg with ground pressures in excess of 100 kPa. Combine parameters such as component weights and locations from axles were analyzed relative to axle loads using simple linear correlation and multiple regression. Results indicated that header and grain parameters are dominant factors influencing axle loads. Combine designers can certainly use these relationships as a guide for future machine improvements. Six alternative harvesters were evaluated and compared to a standard combine based on factors of cost, operation, performance, service, and soil compaction potential. Using these factors, a grading scale was developed to rank the alternatives. Results indicated that two of the alternatives might be feasible if cost effective: (1) a combine with full-length tracks, and (2) a combine with trailing grain cart and weight equally distributed among three axles. However, for a wheeled combine having the harvesting capacity of today\u27s largest machines, four or more axles are necessary to minimize soil compaction, unless total weight can be reduced