Greenhouse gas emissions of sewage sludge land application in urban green space: A field experiment in a Bermuda grassland.

Sewage sludge land application is recognized as a strategy for recycling resource and replenishing soil nutrients. However, the subsequent greenhouse gas emissions following this practice are not yet fully understood, and the lack of quantitative research and field experiments monitoring these emissions hampers the establishment of reliable emission factors. This study investigated the greenhouse gas emission characteristics of sewage sludge land application through a field experiment that monitoring soil greenhouse gas fluxes. Seven nitrogen input treatments were implemented in a typical Bermuda grassland in China, with D and C representing the amendment of digested and composted sludge, respectively, at the nitrogen input rate of 0, 100, 200, and 300 kg N ha. Soil CH, CO, and NO fluxes were measured throughout the entire experimental period, and soil samples from different treatments at various growth stages were analyzed. The results revealed that sewage sludge land application significantly increased soil NO and CO emissions while slightly reducing soil CH uptake. The increased CO emissions were biogenic and carbon-neutral, mainly due to enhanced plant root respiration. The NO emissions were the primary greenhouse gas emissions of sewage sludge land application, which were mainly concentrated in two 50-day periods following base and topdressing fertilization, respectively. NO emissions following base fertilization by rotary tillage were substantially lower than those following topdressing fertilization. A logarithmic response relationship between N input rates and increased soil NO emissions was observed, suggesting lower NO emissions from sewage sludge land application compared to conventional N fertilizers at the same N input level. Future field experiments and meta-analysis are necessary to develop reliable greenhouse gas emission factors for sewage sludge land application.