Nitrogen Migration from Deep-Row Biosolids Incorporation on a Hybrid Poplar Tree Farm

Deep row incorporation of biosolids at rates of 383-658 Mg/ha(171 to 294 dry tons per acre) using hybrid poplar involves the placement of biosolids into trenches that are immediately covered with overburden, eliminating odor problems and maintaining the biosolids in a fairly stable, anaerobic environment. The site is then planted with hybrid poplar trees, the roots of which provide a natural recycling system that utilizes the nutrients over a six-year period in most cases.For three years, nitrate beneath the trenches was essentially zero. Subsequently, nitrate concentration increased to between 1 and 10 mg/L. Ammonium in the suction lysimeters remained between 100-600 mg/L from March 2003 until August 2004, when there was a peak in the highest application rate to 800 mg/L from November 2004 to September 2005. Ammonium concentration is clearly decreasing with distance from the biosolids for all treatments, with significant differences between treatments becoming apparent from November 2003 to November 2005. Ammonium levels in October 2006 at 15 and 60 cm may have stabilized or decreased slightly to 1900 and 400 mg/L, respectively. While ammonium levels at 30 and 60 cm may have leveled off, additional suction lysimeters were installed during the summer of 2007 at 120 cm below the biosolids trench in all plots to better understand ammonium movement in the profile.