Leaching Potential of Nitrogen and Phosphorus in Deep Row Biosolids Incorporation Technology in Coastal Plain Mine Reclamation Sites in Virginia.

Our research was conducted to quantify the leaching potential of nitrogen and phosphorus in deep row incorporation of biosolids for the production of hybrid poplar as a potential bioenergy crop. The study is being conducted on a mineral sands mine reclamation site near the Coastal Plain-Piedmont fall line in, Dinwiddie County, Virginia. The experimental design consists of 8 treatments – two biosolids types each applied in subsurface trenches at two rates, three conventional fertilizer nitrogen application rates, and an unamended control. Application rates were 328 and 656 Mg ha^-1 for the lime-stabilized biosolids, 213 and 426 Mg ha^-1 for the anaerobically digested biosolids, and 168 kg N ha^-1 yr^-1, 337 kg N ha^-1 yr^-1 and 504 kg N ha^-1 yr^-1 for the conventional fertilizer. Each treatment was replicated four times and arranged in a randomized complete block design. The site has been instrumented with suction and zero-tension lysimeters for collection and analysis of leachate from which were determined subsurface loss of nitrogen and phosphorus. During the years of 2006-2008 following study establishment, initial nitrogen loss occurred largely as ammonium and organic N, with the average values of total Kjeldahl nitrogen reaching a peak of 746 mg L^-1 in September 2006. After one year, nitrogen loss occurred mostly as nitrate N, with the maximum average value of 646 mg L^-1 in May 2008. Following an initial spike of total Kjeldahl phosphorus (1.38 mg L^-1) in the leachate from the biosolids treatments in August 2006, total and dissolved phosphorus concentrations rapidly decreased to insignificant levels. The deep row biosolids incorporation technology does not appear to be protective of groundwater nitrate quality when the practice is applied to coarse-textured soils.