Liming and nutrient supply properties of N-Viro treated sewage sludge

The N-Viro process involves the mixing of de-watered sewage sludge (25% dry matter) with alkaline admixtures. Following an exothermic chemical reaction the material is dried by windrowing or by mechanical drying, to produce a pasteurised and dried product (60% dry matter). This is a potentially valuable material in terms of its neutralising value, nutrient content and organic matter. The primary objectives of the research were to evaluate N-Viro's efficiency in neutralising soil acidity and to study nitrate leaching losses and effects on crop yield following autumn application. N-Viro was applied to acidic grassland and compared to ground calcium limestone, ground magnesium limestone and chalk all applied at an equivalent NV loading and an untreated control. Soil pH was measured monthly over a 12 month period. A similar increase in soil pH was observed with the N-Viro and chalk treatments. In addition, the concentration of extractable P in the soil (measured as acetic acid soluble P) was increased with the N-Viro and chalk treatments. The nitrate leaching studies tested N-Viro, ammonium nitrate, farmyard manure and liquid digested sludge applied at similar N loadings in the autumn, and an untreated control. Nitrate leaching losses from a sandy soil at ADAS Gleadthorpe (Nottinghamshire, UK) cropped with winter barley were measured using porous ceramic cups. Nitrate leaching losses for autumn applied N-Viro were similar to farmyard manure, and both were considerably lower than for liquid digested or ammonium nitrate. Crop yields from the N-VIRO and liquid digested sludge treatments were greater than the control or inorganic N treatments.