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Keywords:

  • anaerobic digestion slurry;
  • greenhouse;
  • methane emission;
  • paddy field

Abstract

One hundred million tons of farm stalk waste and livestock and poultry excrement are used every year in China for the production of clean energy (biogas) by anaerobic digestion. Consequently, a large amount of fermented liquid is produced, and if disposed of improperly, it will result in secondary pollution. Agricultural application of this anaerobic slurry as a liquid fertilizer would reduce possible eutrophication of water sources from random slurry discharge and supply a superior organic fertilizer for farming. This study investigated the effect of applying anaerobic digestion slurry as a liquid fertilizer on the methane emitted from a paddy field. A two-year (2008–2009) field experiment replacing chemical fertilizer with liquid fertilizer from anaerobically digested pig manure slurry was conducted in a paddy field in Yixing, Jiangsu, China. A static closed chamber method was used to measure methane fluxes over the period from June 2008 to October 2009. All fertilizer treatments increased methane emissions relative to untreated controls, with increases in methane ranging from 40–70% in 2008 to 48–84% in 2009. Paddy fields treated with anaerobically digested pig manure slurry had greater methane emissions (8–84% in 2008 and 3–26% in 2009) than those treated with chemical fertilizer. This suggests that the anaerobic digestion slurry would increase methane emission and so is unsuitable as a liquid fertilizer in paddy fields without development of cultivation practices to limit these emissions.