Ammonia, methane, and nitrous oxide emission from pig slurry applied to a pasture in New Zealand

Abstract

Much animal manure is being applied to small land areas close to animal confinements, resulting in environmental degradation. This paper reports a study on the emissions of ammonia (NH₃), methane (CH₄), and nitrous oxide (N₂O) from a pasture during a 90-d period after pig slurry application (60 m³ ha⁻¹) to the soil surface. The pig slurry contained 6.1 kg total N m⁻³, 4.2 kg of total ammoniacal nitrogen (TAN = NH₃ + NH₄) m⁻³, and 22.1 kg C m⁻³, and had a pH of 8.14. Ammonia was lost at a fast rate immediately after slurry application (4.7 kg N ha⁻¹ h⁻¹), when the pH and TAN concentration of the surface soil were high, but the loss rate declined quickly thereafter. Total NH₃ losses from the treated pasture were 57 kg N ha⁻¹ (22.5% of the TAN applied). Methane emission was highest (39.6 g C ha⁻¹ h⁻¹) immediately after application, as dissolved CH₄ was released from the slurry. Emissions then continued at a low rate for approximately 7 d, presumably due to metabolism of volatile fatty acids in the anaerobic slurry–treated soil. The net CH₄ emission was 1052 g C ha⁻¹ (0.08% of the carbon applied). Nitrous oxide emission was low for the first 14 d after slurry application, then showed emission peaks of 7.5 g N ha⁻¹ h⁻¹ on Day 25 and 15.8 g N ha⁻¹ h⁻¹ on Day 67, and decline depending on rainfall and nitrate (NO₃) concentrations. Emission finally reached background levels after approximately 90 d. Nitrous oxide emission was 7.6 kg N ha⁻¹ (2.1% of the N applied). It is apparent that of the two major greenhouse gases measured in this study, N₂O is by far the more important tropospheric pollutant.