Organic matter accumulation post‐mineral sands mining

Soil development and organic matter (OM) accumulation are vital for sustainability in reclaimed prime farmlands following mineral sands mining. Additionally, the effectiveness of soil reconstruction techniques on soil development greatly influences crop productivity. Soil development and management effects following mineral sands mining were evaluated in years 1 (2005), 4 (2009) and 6 (2011) at the Carraway‐Winn Reclamation Research Farm, VA, USA. Treatments for this full scale agricultural experiment are as follows: biosolids applied at a rate of 78 Mg/ha managed with conventional tillage (BIO‐CT) and no‐till (BIO‐NT), a 15‐cm topsoil cap (TS), and a lime + fertilized control. Crop yields were determined annually, and soils were collected and analysed for aggregate size distributions and OM pools (available, aggregate‐protected and mineral‐bound). Crop yields (Corn‐Zea mays and wheat/soybean‐Triticum aestivum/Glycine max) were generally larger in the biosolids treatments from 2005 to 2008, with no difference among treatments from 2009 to 2011. Whole soil carbon (C) and nitrogen (N) rapidly increased between 2005 and 2009, mainly in the large macroaggregate (2000–8000 μm) size fraction. Carbon accumulation rates in the whole soils ranged from 2.85 to 3.58 Mg C/ha in the first 4 yr of soil development (similar trends were observed for N). There were no differences for soil aggregate parameters among treatments until year 6, where biosolids treatments contained more microaggregate (53–250 μm) and mineral‐bound C and N relative to other treatments. Short‐term increases in crop yields and long‐term increases in stable soil C and N make biosolids applications a viable alternative to traditional TS replacement strategies for this mining land use scenario.