EFFECTS OF BIOSOLIDS LOADING RATE ON NITRATE LEACHING POTENTIALS IN SAND AND GRAVEL MINE RECLAMATION IN VIRGINIA

摘要

The USEPA 503 biosolids utilization rules recognized the need for higher than agronomic rate applications to mined lands under the assumption that NO3-N contamination of ground-water will not be significant. We evaluated a range of biosolids loading rates (1x to 7x agronomic rate of 14 Mg/ha) with and without added sawdust (to adjust the applied C:N ratio to approximately 20:1) on a reclaimed gravel mined soil and an undisturbed prime farmland soil for three growing seasons. The two experimental blocks were cropped to corn (Zea mays) in 1996, and winter wheat (Triticum aestivum) and soybeans (Glycine max) in 1997. Root zone leachates were collected from zero-tension lysimeters under adjacent identically treated micro-plots. Effects of biosolids loading rate on crop yields were not as pronounced as expected due to relatively wet weather. Leachate NO3-N over the winter of 96/97 increased incrementally (from < 20 to > 100 mg/L) with loading rate (1x to 7x) and then declined sharply in March and April of 1997, finally approaching control level concentrations through the winter of 1997/1998 and beyond. Addition of sawdust significantly decreased NO3-N leachate levels at all biosolids loading rates except the 5x biosolids + sawdust treatment which exhibited a first winter spike in excess of 100 mg/L. Mass leaching losses of NO3-N ranged from 6 to 60 kg/ha, which was from 0.7 to 3.1% of total- N applied. These data indicate that higher than agronomic loading rates of biosolids do lead to enhanced NO3-N leaching potentials over the first winter following application. However, this “one-time event” supports the original USEPA presumption that some net leaching under elevated loading rates is to be expected, but it is a short-term, low magnitude effect.