Bulk Density of Rocky Mine Soils in Forestry Reclamation

The Forestry Reclamation Approach (FRA) for reclaiming surface mined lands in Appalachia recommends minimal grading of mine soil materials to avoid surface compaction, which maintains an open and loose material for tree root expansion. To determine the level of compaction of mine soils, bulk density is measured. The traditional method of soil cores for measuring bulk density is difficult and prone to errors in rocky materials used for mine reclamation. We selected four methods (foam, frame, sand cone, and radiation) to determine bulk density at a depth of 15 cm in four mine soils and one forest soil, all having rock fragment contents > 30%. Bulk density values by sand cone were significantly lower (average of 1.35 Mg m−3) than bulk densities determined by the other three methods (averages of 1.64–1.76 Mg m−3). The sand cone was lower because the metal plate was sometimes not flush with the soil surface because of rock protrusions. For soils, the native forest soil showed an average bulk density across methods of 1.05 Mg m−3, while the mine soils ranged from 1.70 to 1.84 Mg m−3. Standard deviations for each method across soils (n = 25) ranged from 6% for radiation to 19% for the sand cone. In-field time efficiency was shortest for the radiation method at 6 min per sample, compared with 10 min for foam, 14 min for sand cone, and 27 min for the frame. The radiation method had the lowest standard deviation (better reproducibility) and better time efficiency than the other methods.