Impact of Soil Reconstruction Method On Nitrate Accumulation in Forages Grown for Livestock Feed.

Past research has shown that the use of biosolids in the reclamation of drastically disturbed lands has increased forage yield and nutritive value with no detrimental effects on soils, vegetation, or water quality.  One potential concern when using high rates of biosolids in reclamation programs is the accumulation of concentrations of nitrate in the forage tissue that could be dangerous or even toxic to ruminant livestock (>0.5%).  Past reclamation research in which biosolids have been used has not assessed these levels.  The objective of this research was to determine the impact of soil reconstruction method on the concentrations of nitrate in forage tissue.  This research was conducted at a mineral sands mine located in Dinwiddie County, VA.  Soil reconstruction treatments were 1) Control: rip, lime, P, and routine fertilization per crop management protocols, 2) Biosolids: rip, lime stabilized biosolids at 78 dry Mg per hectare, and routine fertilization per crop management protocols, and 3) Topsoil: rip, lime, P to subsoil, 15.25 cm of topsoil return, and routine fertilization per crop management protocols.  The levels of biosolids used in this experiment resulted in the accumulation of high levels of nitrate in the forage tissue.  One year after the soil reconstruction treatments were imposed and the plots were seeded to a grass-legume mixture, levels of nitrate in forages treated with biosolids were 2.5% (NO₃^-).  This is in the toxic range for ruminant livestock and these forages should not be fed.  Initial results indicate that when biosolids are used in a reclamation program, forage must be carefully monitored for accumulation of nitrates in order to avoid potential livestock fatalities.