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 anae robically 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 stead y-state hydrological conditions. Two 24 h, 4.5 mm h(-1) rainfall events, wi th 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)) wer e significantly greater (P less than or equal to 0.05) than during event 2 (6.4-11.9 mg kg-l). Phosphate losses were significantly greater (P less tha n or equal to 0.05) during event 2 (up to 0.30 mg kg(-1)) compared to the f irst (< 0.05 mg kg(-1)). The sand soil showed similar effects. Losses of ni trate-N (percentage of total N applied) from the sand soil were small (arou nd 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 bioso lid had little impact on nitrate and phosphate losses from soil compared to fresh MAD biosolid. The effect of composting MAD biosolid on nutrient loss es was more variable. (C) 2001 Elsevier Science Ltd. All rights reserved.