Nitrous oxide and carbon dioxide emissions from grassland amended with sewage sludge

Land disposal of sewage sludge in the UK is set to increase markedly in the next few years and much of this will be applied to grassland. Here we applied high rates of digested sludge cake (1–1.5×10 3 kg total N ha −1 ) to grassland and incorporated it prior to reseeding. Using automated chambers, nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) fluxes from the soil were monitored 2–4 times per day, for 6 months after sludge incorporation. Peaks of N 2 O emission were up to 1.4 kg N ha −1 d −1 soon after incorporation, and thereafter were regularly detected following significant rainfalls. Gas emissions reflected diurnal temperature variations, though N 2 O emissions were also strongly affected by rainfall. Although emissions decreased in the winter, temperatures below 4 °C stimulated short, sharp fluxes of both CO 2 and N 2 O as temperature increased. The aggregate loss of nitrogen and carbon over the measurement period was up to 23 kg N ha −1 and 5.1 t C ha −1 . Losses of N 2 O in the sludge‐amended soil were associated with good microbial conditions for N mineralization, and with high carbon and water contents. Since grassland is an important source of greenhouse gases, application of sewage sludge can be at least as significant as fertilizer in enhancing these emissions.