biosolids application in BC

By Emma Avery, Faculty of Land and Food Systems, University of British Columbia

Semiarid grasslands around the world are among the ecosystems with the highest species richness and provide a wide range of ecosystem services. They play an important role within the global carbon cycle, provide forage for livestock, facilitate water infiltration and regulate hydrological cycles. In British Columbia (BC), grasslands occupy a relatively small proportion of the province’s land base, located primarily in the southern interior. In some cases, these unique ecosystems have been substantially altered following the introduction of livestock by European settlers in the mid-19th century, and some continue to be impacted today by urban development, crop production, recreation, and overgrazing. Once degraded, grasslands can take a long time to recover; large areas of grasslands in the interior of BC still show the effects of extensive overgrazing that occurred over a century ago (Wikeem & Wikeem, 2004).

In 2001, a study on the effects of a rangeland biosolids application on plant community composition and production was initiated in the southern interior of BC by Dr. Reg Newman (Newman et al., 2014). Three sites were established on grasslands where extensive grazing had taken place, in Ashcroft, Merritt, and Jesmond. At each site, 4 blocks were excluded from cattle grazing with fencing, and biosolids were applied at a rate of 20 Mg per hectare to one half of each of the blocks. The other half did not receive biosolids and served as a control. The plant communities at the Merritt and Ashcroft sites (which were drier and contained invasive cheatgrass at the time of application) showed a negative response to the biosolids application 4 and 5 years after the application, respectively. However, native perennial bluebunch wheatgrass at the Jesmond site increased significantly under the biosolids 4 years after the application.

biosolids application in Jesmond, BC
An exclosure at Jesmond in 2016: bluebunch wheatgrass growing on the right side, which was amended with biosolids in 2001.

Fourteen years after a single application, the positive impact of biosolids on the site’s forage production remains evident. A joint team of researchers from the Ministry of Forests, Lands, Natural Resource Operations, and Rural Development (FLNRORD) and the University of British Columbia’s Soil Science group returned to the site in 2016 to collect data on soil quality indicators such as structural stability, soil carbon, soil moisture, and plant available nutrients. Soil samples were collected in April, June, August and October 2016, while plant species composition and above ground biomass were assessed in June 2016.  Aboveground plant biomass was almost two times greater on the plots with biosolids application than on the control, due entirely to increased growth of grass, not forbs. Despite differences in aboveground biomass there was no difference in total soil carbon. However, biosolids amended soil did exhibit a greater ability to retain soil water at high tensions, and a significantly lower pH. Available phosphorus was the only macronutrient that was significantly higher in the biosolids treatment 14 years after application relative to the control. The increased soil water and available phosphorus may be the cause for sustained high levels of forage production.  The more resource-rich soil environment may have especially benefitted an agronomic perennial, Kentucky bluegrass, which now covers 25.83 ±13.83% of the biosolids blocks, and less than 1% of the control. This study showed that a single biosolids application led to greater forage yields and improved aspects of soil quality 14 years following that application; however, this also led to a change in plant species composition, which may be less desirable from a restoration perspective.

soil sampling in Jesmond, BC
Soil sampling underway at the study site.

While these results are preliminary, this research will aim to illuminate the edaphic mechanisms that have increased long-term plant productivity on a degraded semi-arid grassland site after a one-time biosolids application. It is hoped that the findings will be of use in the ongoing discussion as to how to best manage BC’s grasslands.

Funding for this project was provided in part by Metro Vancouver and BC Ministry of Forests, Lands, Natural Resource Operations and Rural Development.