Cover crops can improve soil quality through protection against erosion, addition of both high C:N and low C:N residues, soil loosening through deep or pervasive root systems, increased microbial diversity, improved soil nutrient cycling or additions of biologically-fixed N.  A 5-yr study was conducted to investigate the effects of cover crop species and cropping intensity on soil quality and N availability in four broccoli-squash rotations.   Treatments included rotations with cover crops present between 0% and 65% of the time.  Cover crop species included red clover (Trifolium pretense L.), hairy vetch (Vicia villosa Roth) and winter rye (Secale cereale L.).    The following soil quality measurements were taken at the initiation of the trial and again each year in late May in all cropped fields:  water infiltration rate, water holding capacity, soil bulk density and soil penetrometer resistance.  Particulate organic matter (POM) and aggregate stability was measured at the end of year 5 in all treatments.  NO₃^- and NH₄⁺ was measured biweekly throughout the growing season each year.  Soil quality data showed improvement in bulk density, water holding capacity, POM and aggregate stability that was positively correlated to the length of time each treatment was in cover crops in the rotational cycle.  The conventional broccoli-squash rotation, which had no cover crops, showed decreased soil quality in most measurements over the same time period.