Factors Affecting Ammonia Volatilization from Sewage Sludge Applied to Soil in a Laboratory Study

A forced-air polyvinyl chloride (PVC) cylinder manifold chamber was used to collect ammonia (NH₃) volatilized from sewage sludges applied to soil in the laboratory. A series of experiments were conducted in which the effect on NH₃ volatilization of a single variable was studied. The reference control conditions were: Columbus, Ohio anaerobically digested liquid sewage sludge applied at 5 Mg ha⁻¹ (dry wt) to a Crosby silt loam soil (pH 6.7) at 0.01 MPa initial moisture tension. The soil was bare and the sludge was unincorporated during the 24-h study period. Air temperature was 26 ± 2°C. The variable conditions were: (i) initial soil moisture (0, 0.01, 1.5 MPa and air-dry); (ii) time of incorporation (0.25, 1, 3, 6, 12, and 24 h after sludge application); (iii) soil pH (5.1, 6.7, 7.5); (iv) sludge type (anaerobically digested Columbus liquid sludge, partially dewatered Columbus anaerobic sludge, aerobically digested Medina liquid sludge, lime stabilized primary Ashland sludge, and composted primary Columbus sludge); (v) temperature (12.8, 18.3, 26.7°C); and (vi) vegetative cover [bare, grass sod (Poa pratensis), wheat straw (Triticum aestivum)]. Initial soil moisture contents ≤1.5 MPa tension increased NH₃ volatilization compared with air-dry soil. Volatilization increased linearly with time elapsed before sludge incorporation. Ammonia loss was greater from soil at pH 7.5 than at pH 6.7 or 5.1. There was significantly greater loss of NH₃ from the lime-stabilized sludge (pH 12) than from the anaerobic and aerobic sludges. No detectable NH₃ was lost from the compost. Volatilization decreased with decreasing temperature. When the sludge contained large sludge particles, NH₃ loss increased with vegetative cover. However, cover had no effect when the sludge was well homogenized. For all experiments, 24-h volatilization losses ranged from 0 to 32% of the NH₃-N applied.