Nutrient Leaching following Land Application of Aerobically Digested Municipal Sewage Sludge in a Northern Hardwood Forest
- L. Medalie,
- W. B. Bowden * and
- C. T. Smith
Concentrations of selected cations and anions were determined in soil solutions from a forested site in southern New Hampshire during the first growing season after surface application of an aerobically-digested, limed, liquid municipal sludge. Sludge was applied in June 1989 at 0, 3.3, 6.9, and 14.5 Mg ha−1, which corresponded to 199, 396, and 740 kg N ha−1 as total Kjeldahl N (TKN). Porous, suction-cup lysimeters were used to sample soil solutions below the rooting zone (≈60cm) within subplots designed to include (untrenched) exclude (trenched) uptake by vegetation. Following sludge application, measured solute concentrations remained low until September 1989, when NO3, Cl, Ca, Mg, Na, and K in trenched subplots increased simultaneously to maximum values in October or November 1989, just before the soil froze for the winter. Nitrate was the dominant anion in soil solutions from trenched subplots and averaged in excess of 0.71 mmol L−1 (10 mg L−1 NO3-N) at all loading rates. Highest concentrations of NO3 occurred on subplots with the highest sludge application rates. In the untrenched areas, NO3 concentrations rarely exceeded 0.001 mmol L−1; Cl increased in treated areas and was the dominant anion by the end of the season. Soil solution NH4, PO4, SO4, K, and pH did not change significantly for any sludge application rate. Comparison of results from trenched and untrenched areas suggests that, at application rates of up to 14.5 Mg ha−1 (799 kg TKN ha−1), a combination of physical, chemical, and biological factors (most likely plant uptake) limited the movement of sludge or sludge-derived constituents from the sites of application.
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