Sawdust Biochar Trial for Trees Growing in Mine Soils.

Biochar has been found to improve crop productivity in some situations by enhancing soil physical, chemical and biological properties. Tree species on lands reclaimed following surface mining for coal in the Appalachian coal basin often have low survival and growth rates due to soil limitations, including low concentrations of soil carbon. Biochar application to these lands might improve their productivity by correcting these limitations. Biochar made from pine (Pinus spp.) sawdust in a fast pyrolysis process was applied at rates of 0, 2.3, 11.2 and 22.5 Mg Ha^-1 to three types of mine soils to test its effects on their properties and the growth of American sycamore (Platanus occidentalis) and black locust (Robinia pseudoacacia). One mine soil was derived from brown sandstone, one from brown and gray sandstones and one from siltstone, brown sandstone and gray sandstone.  Thirty cm incubation columns were constructed with combinations of these mine soils and biochar rates, plus a pure biochar control, and were weathered in the laboratory  for six months with 2.5 cm of collected rain water added weekly. Additionally, the combinations of mine soil and biochar, plus a pure biochar medium, were used to grow American sycamore and black locust in a greenhouse for one growing season by both topdressing and finely incorporating the biochar into the mine spoils. The pure biochar medium allowed 100% survival of all trees while showing improvements in above ground woody biomass growth (3470% for black locust) and below ground biomass, suppressed competing herbaceous biomass and significantly increased volumetric water holding capacity (49.8%), soil carbon and organic matter following one season of incubation (p < 0.05). Pure biochar created the most consistently high saturated hydraulic conductivity rates. Significant effects of lesser rates of biochar application were limited, but there was a general trend of it increasing available potassium, carbon and organic matter while decreasing available phosphorus, calcium and iron. Weathering with rainwater decreased soluble salts by a factor of approximately two for nearly all biochar x mine soil treatments, regardless of biochar application rate. Biochar may be more useful as an amendment if concentrated in tree planting holes than if broadcast across entire reclaimed mined sites.