Using organic amendments to restore soil physical and chemical properties of a mine site in northeastern Oregon, USA

New cost-effective strategies are needed to reclaim soils disturbed from mining activity on National Forests. In addition, disposal of waste wood from local timber harvest operations or biosolids from waste water treatment plants can be expensive. Therefore, using organic byproducts for soil reclamation activities on National Forests may provide an opportunity to increase soil cover and productivity, and decrease restoration costs. To test the effectiveness of these amendments for reclamation, a field study was established using organic amendments applied to gold dredgings capped with 10 cm of loam and with little regenerating vegetation within the Umatilla National Forest in northeastern Oregon. Study plots had biochar (11 Mg/ha), biosolids (17 Mg/ha), or wood chips (22 Mg/ha) applied singly or in combination. Each plot was divided in half. One half of the plot was seeded with native grasses and forb and the other half was planted with a combination of California brome (Bromus carinatus Hook & Am.) and Jepson's blue wildrye (Elymus glaucus Buckl.). After two growing seasons, there were no significant differences in plant cover between the planted or seeded plots. Biosolids, biosolid + biochar + wood chips, and biosolid + wood chips had greater grass and forb planted cover after two years; seeded plots on the biosolid + biochar + wood chips and biosolid + wood chip treatments had the greatest grass and forb cover. Soil properties were significantly altered by individual treatments; combination treatments improved nutrient availability and soil moisture, resulting in up to twice as much plant cover than in the control plots. Forest managers can produce biochar and wood chips from the abundant forest waste generated during harvest operations, and class "A" biosolids are available in Oregon from local municipalities. Using these three amendments in combination to restore disturbed mine soils can provide an affordable and effective strategy.