The purpose of this study was to determine the effects of soil compaction on the chemical properties of soil and herbage yield of lucerne (Medicago sativa L.). A field experiment was conducted on a silty loam Mollic Fluvisols soil in 2003-07. Four compaction treatments were applied three times annually by tractor using the following number of passes: control without experimental traffic, two passes, four passes, and six passes. This study confirmed the unfavorable effect of multiple tractor passes on lucerne dry matter production. The results showed that tractor traffic reduced the yields of lucerne, particularly during the second and third harvests in each year. Soil compaction caused by tractors changed some chemical properties of soil. Tractor passes resulted in increasing pH and EC. It also increased P and Zn content. Most of these changes were statistically significant only in the deeper 20-30 cm soil layer. This effect could be ascribed to higher soil density and lower air permeability. The upper (0-20 cm) soil layer was resistant to changes in chemical properties, probably due to the dense root system that recovers the soil after compaction and improves physical properties. The decrease in lucerne production probably was the result of mechanical damages to roots and above-ground parts of plants rather than problems in nutrient uptake. We can conclude that chemical properties, particularly N content, are not significantly important factors in reduction of lucerne production exposed to tractor traffic.