Comparison of the effect of surface application and subsurface incorporation of enhanced treated biosolids on the leaching of heavy metals and nutrients through sand and sandy loam soils

Use of enhanced treated biosolids such as composted and dried, mesophilic anaerobically digested, dewatered (MADD) biosolids is becoming more popular. This is mainly in response to concerns over the potential for pathogens to enter the food chain. There is, therefore, a need to investigate how enhanced treatment, and methods by which these biosolids are applied, affects the leaching potential of metal and nutrients to ensure that water quality is not compromised. MADD cake (fresh, dried and composted) and MAD liquid sludge were applied by surface application and subsurface incorporation to sand (typic quartzipsamments, %OM = 3.0, pH = 6.5), sandy loam (typic hapludalf, %OM = 4.8, pH = 7.6) and silversand 'repacked semi-structured cores' (0.2 in by 0.1 m diameter) at rates equivalent to 250 kg N ha(-1) yr(-1). Leaching of Zn, Cu, Pb, Ni, N and P was investigated following application of five 8 h simulated rainfall events (4.9 nun h(-1)) in the laboratory. Little difference was observed between leaching of metals and nutrients from soils amended with enhanced treated biosolids (dried and composted MADD cakes) compared with conventional biosolids (fresh MADD cake and MAD liquid). Subsurface incorporation increased the risk of P and metal leaching compared with surface application. Nitrate losses were independent of application method. Similar nutrient losses from control and amended cores indicated that the leaching was derived predominantly from the soil clay and organic matter complexes. Evidence for attenuation of biosolids-derived metals and P by soil-derived clay and/or organic matter was found. Water balance data showed that hydrological regimes of each core were comparable and unlikely to account for observed differences in leaching losses.