Effect of drying and composting biosolids on the movement of nitrate and phosphate through repacked soil columns under steady-state hydrological conditions

Effects of two "enhanced" treatments (drying and composting mesophilic anaerobically digested (MAD) biosolid) on nutrient leaching were investigated. Repacked sandy or sandy loam textured soil cores amended with fresh, dried and composted MAD biosolid (250 kg N ha(-1)), were investigated under steady-state hydrological conditions. Two 24 h, 4.5 mm h(-1) rainfall events, with a 14-day interval, were simulated using water-tracers. Losses of nitrate from the sandy loam soil during rainfall event 1 (43.9-68.0 mg kg(-1)) were significantly greater (P < or = 0.05) than during event 2 (6.4-11.9 mg kg(-1)). Phosphate losses were significantly greater (P < or = 0.05) during event 2 (up to 0.30 mg kg(-1)) compared to the first (< 0.05 mg kg(-1)). The sand soil showed similar effects. Losses of nitrate-N (percentage of total N applied) from the sand soil were small (around 0.06% for fresh/dried and 0.63% for composted MAD biosolids). Losses of nitrate-N from the sandy loam soil were greater; 4% for fresh and dried and 3% for composted MAD biosolids. This research showed that drying MAD biosolid had little impact on nitrate and phosphate losses from soil compared to fresh MAD biosolid. The effect of composting MAD biosolid on nutrient losses was more variable.