The response of grain yield and root growth of spring barley to changes of compaction and aeration of a sandy soil was studied under model conditions. The experiment was done using plots of 1 m x 1 m. The results show that ODR was significantly negatively correlated with bulk density. However, bulk density affects both the mechanical impedance to root growth and the ODR. In our experiments it was not possible to separate these different effects of bulk density. The optimum bulk density for both root growth and grain yield was found to be 1.43 Mg m-3. Grain yield was linearly related to root mass.