Differing effects of biosolids on native plants in grasslands of southern british columbia

The objective of this study was to determine if application of biosolids is beneficial for restoring semiarid grasslands. The effects of a one-time surface application of biosolids at a rate of 20 Mg ha on individual plant species and plant community composition were examined at three degraded semiarid grassland sites located in the southern interior of British Columbia, Canada. Biosolids application did not result in desirable changes in plant species composition at the two drier sites (with annual precipitation <400 mm) yet led to overall positive plant species changes at the least dry site (with annual precipitation of 400 mm). An important late-seral species of semiarid grasslands, bluebunch wheatgrass [ (Pursh) Á. Löve], did not respond or decreased at the two drier sites but increased at the least dry site. Exotic invasive plant species increased on all sites. The total vegetative cover of native perennial grasses increased from 41 to 99% at the least dry site, with important decreases in low-growing, early-seral forb species. Although cheatgrass ( L.) was not significantly increased by the biosolids treatment, the dominance of cheatgrass and lower growing season precipitation at the two drier sites were likely key reasons for the poor biosolids restoration success at these sites. Despite some concerns, there is potential to use biosolids to restore grassland plant communities successfully within 4 or 5 yr on more mesic grassland sites; however, biosolids use on drier sites where exotic invasives are present cannot be recommended.