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UBC Theses and Dissertations

The long-term effects of biosolids on rangeland soil quality and plant community in the central Interior of British Columbia Avery, Emelia


Biosolids have been shown to improve forage production and soil quality on semi-arid rangelands in the short-term. The objective of this study was to assess the long-term effects of a single, surface biosolids application on rangeland soil quality, forage production and plant community composition. In 2002, the experiment was established on a ranch in the central Interior of British Columbia, where two treatments were evaluated: surface biosolids application at 20 Mg ha-¹ and a control (no biosolids). Both treatments were replicated in four blocks, which were then excluded from grazing for 14 years. In 2016, soil samples were collected in April, June, August and October to assess various soil quality indicators, while forage quality indicators were assessed in June 2016. Fourteen years following the biosolids application, aboveground plant biomass was almost two times greater with biosolids application than on control. Exposed mineral soil was significantly decreased in biosolids plots. Despite differences in aboveground biomass there was no difference in total soil C, permanganate-oxidizable C, or aggregate-protected total C and polysaccharides contents between biosolids and control plots. However, biosolids amended soil did exhibit significantly greater aggregate stability, lower pH, increased spring soil water content, and increased availability of soil P, Fe, Zn and Cu. Forage grown on biosolids plots had lower protein concentrations than control plots, but greater total protein due to the greater biomass. The biosolids application resulted in higher cover of native bluebunch wheatgrass in the long-term, along with >25% cover of agronomic perennial, Kentucky bluegrass. These results offer a demonstration of the potential long-term improvement in forage production that can occur under biosolids application without grazing, which was accompanied by somewhat mixed effects on soil quality and plant species composition.

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