Emissions of Nitrous Oxide, Methane and Ammonia After Field Application of Digested and Dewatered Sewage Sludge With or Without Addition of Urea

Abstract

By recycling sewage sludge (SS) to productive land, its plant nutrients can be utilised. However, the use of organic fertilisers carries health risks and causes emissions of nitrous oxide (N2O), methane (CH4) and ammonia (NH3). One measure to sanitise SS from human pathogens is addition of NH3. Mesophilically digested and dewatered SS treated with urea and stored, or only stored, was applied to arable land in spring and autumn, respectively, and the effects of immediate or delayed incorporation (by 4 h) on emissions of N2O, CH4 and, in spring, NH3 were investigated. N2O emissions in autumn from soil treated with SS were significantly higher than from soil without SS application (0.09, 1.31 and 0.68 kg N2O-N ha−1 for control, immediate and delayed incorporation, respectively). These emissions were significantly correlated with volumetric water content in soil. Corresponding N2O emissions in spring were 0.15, 0.57 and 0.41 kg N2O-N ha−1. Delayed incorporation (0.20 and 0.34 % of added N in spring and autumn, respectively) tended to reduce N2O emissions compared with immediate incorporation (0.32 and 0.71 % of added N in spring and autumn, respectively). Nitrous oxide emissions from SS were apparently lower after spring than after autumn application, likely because of drier soil and crop uptake of nitrogen in spring. Methane emissions were negative or negligible. Timing of incorporation had no statistically significant effect on NH3 emissions. Nitrous oxide emissions from soil treated with SS at a rate based on the maximum permissible P level were moderate and CH4 emissions negligible.