Row Crop Response to Soil Reconstruction Methods Following Mineral Sands Mining in Virginia.

Over 1000 ha of productive farmland in Virginia have been disturbed through mineral sands mining operations since 1997. Topsoil return vs. topsoil substitution via organic amendment were tested on an active mine site in Dinwiddie County. Lime-stabilized biosolids (78 Mg ha^-1; with and without conservation tillage) were applied to mine tailings and contrasted against 15 cm topsoil return and lime + N-P-K fertilizer applied directly to tailings. An unmined control plot was established on undisturbed prime farmland. The experiment was cropped to corn (Zea mays) in 2005, winter wheat/soybeans (Triticum aestivum/Glycine max) in 2006 and corn again in 2007.  In 2005, the two biosolids treatments produced highest yields (10,786 and 10,848 kg ha^-1, respectively) followed by the limed and fertilized tailings (8,466 kg ha^-1).  Topsoiled plots (3,763 kg ha^-1) were the lowest yielding treatment. Regardless, all mine soil reconstruction methods were much lower in yield than the unmined prime farmland soils (14,361 kg ha^-1). Surface crusting and low pH (5.7 surface and 5.1 subsoil) were observed on topsoil plots as a result of use of poor quality forest topsoil. Corn yields on all treatments except topsoil exceeded 5-year county average yields (which include non-prime lands). Biosolids treatments produced the highest winter wheat and soybean yields in 2006, while the control and topsoil plots were similar in productivity, but slightly lower than biosolids treatments. Corn yields in 2007 showed poor performance on biosolids (3,449-3,637 kg ha^-1) due to N limitations, while the control and topsoil treatments (7,274 kg ha^-1) were similar to county average yields. Regardless of soil reconstruction approach, a 25 to 30% reduction in productivity should be expected following mining of prime farmlands in this region. However, appropriate application of organic amendments and tillage can produce post-mining soils capable of meeting or exceeding county average yield targets.