The use of biosolids to restore native plant communities in semi-arid grassland

The grasslands of British Columbia are ecologically and economically valuable, but human activities, climate change and environmental disturbances are major pressures causing grassland degradation. Re-establishing native plant communities is critical for restoring disturbed grasslands or post-mine influenced sites. One of the difficulties is that disturbed grasslands, particularly those disturbed by mining activity, have poor quality soil that is not conducive to plant growth. Soil amendments can provide nutrients that help plants grow. As a soil amendment, biosolids, treated solids recovered from municipal wastewater, can improve soil capacities of degraded land and provide the nutrients for plant growth. The objectives of this study were 1) to determine an appropriate rate of biosolids application to promote the colonization of native plants, 2) to test whether additional seeding of cover crops and successional plants in the following year was effective in promoting colonization of plants, and 3) to determine the effects of the biosolids and sowing treatments on soil properties. In 2021, a field study was devised that tested four biosolids application rates (0, 125, 250, and 375 dry Mg/ha) with a seed mix in all test plots in the first year and only half of the test plots in the second year, at two sites selected from the southern interior grasslands of British Columbia. One site was located in a suburban area with four replicates per experimental combination; the other site was located in a mining area with six replicates per experimental combination. Due to differences in environmental conditions between the two sites, the seed mix involved a cover crop and five to four native successional species respectively. This study demonstrated that biosolids significantly increased the productivity and diversity of the plant community, as well as the soil properties. However, higher rates of biosolids did not lead to significantly higher plant productivity and diversity than the lower rates. Results of this study suggest that biosolids may significantly help in restoring sustainable grassland ecosystems in disturbed grasslands and mine sites.