Biosolids application to rangelands and pastures recycles nutrients and organic matter back to soils. The effects of biosolids (20 and 60 dry Mg ha(-)(1)) and N+P fertilizer on soil aggregate stability, bulk density, aeration porosity, and total C and N of stable aggregates were evaluated 4 and 5 yr after surface application to a crested wheatgrass [Agropyron cristatum (L.) Gaertn.] pasture in the southern interior of British Columbia (BC). The experiment was established in 2001 in a randomized complete block design with four replications. The 60 Mg ha(-1) biosolids treatment (Bio 60) had a greater aggregate mean weight diameter (MWD) and proportion of water-stable soil aggregates > 1 mm relative to the control and fertilizer treatments. Temporal variation in aggregate stability was attributed to seasonal variations in soil water content. Surface application of 60 Mg ha(-1) of biosolids increased C concentrations within water-stable aggregates relative to the control from 29 to 104, 24 to 79, and 12 to 38 g kg(-1) for the 2 to 6, 1 to 2, and 0.25 to 1 mm size fractions, respectively. The concentration of N within aggregates increased in similar proportions to C. Neither soil bulk density, nor aeration porosity were affected by biosolids application. Increased aggregation and the accumulation of soil C within aggregates following biosolids application creates a potential for better soil C storage, soil water retention, nutrient availability, and ultimately the overall health of semiarid perennial pastures.

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.

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Biosolids may improve the ecological function of degraded semiarid grasslands, but an understanding of the plant community is essential. An experiment was established in 2001 to determine the effects of a single surface application of biosolids on soil aggregate stability and the composition of the plant community in a semiarid grassland in British Columbia, Canada. Four treatments were evaluated: (i) surface biosolids application at 20 (Bio-20) and (ii) 60 Mg ha (Bio-60), (iii) mineral fertilizer, and (iv) a control. All treatments were replicated in four blocks. Soil was sampled during the spring (May), summer (June-July), and fall (October) in 2005, 2006, and 2009; the plant community was assessed in 2009. The greatest increases in size of stable aggregates relative to the control were in the spring and summer, which coincided with a 1.6- to 2.1-fold increase in the spring concentration of N within stable aggregates when biosolids were applied at 20 and 60 Mg ha , respectively. Nitrogen concentrations from the Bio-60 treatment were not different from the control, but the Bio-20 treatment had 42% greater N than all other treatments during summer. Biosolids application in this ecosystem did not increase perennial forage grass species relative to the control, and when biosolids were applied at a rate of 60 Mg ha there was a 75% reduction in the perennial forage plant species. The application of biosolids to native grasslands in semiarid environments should be done cautiously, especially when winter annual plant species (e.g., cheatgrass [ L.]) are present before application.

Biosolids have been shown to improve forage production and soil quality on semiarid rangelands in the short term, but less is known about longer-term impacts of one-time biosolids applications. The objective of this study was to determine the effects of a single, surface biosolids application (at 20 dry Mg ha−1) on stability of soil aggregates, bulk density, total carbon (C) and nitrogen (N), permanganate-oxidizable carbon (POXC), polysaccharides, pH, nutrient availability, and soil water content (all at 0–7.5 cm depth) 14 yr following application to ungrazed rangelands in the Central interior of British Columbia. Fourteen years following the biosolids application, aboveground plant biomass was almost two times greater with biosolids application than on control, while exposed mineral soil and microbiotic crust significantly decreased in biosolids plots. Despite differences in aboveground biomass, there was no difference in total soil C and N, POXC, and polysaccharides between biosolids and control plots. Biosolids-amended soil did exhibit significantly greater mean weight diameter of water-stable aggregates, lower pH, increased spring soil water content, and increased availability of Fe3+, Zn2+, Cu2+, and phosphate ions. These findings indicate that the long-term improvements to soil on ungrazed rangeland are possible even from a single biosolids application.