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

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

Growth and yield response of glasshouse- and field-grown sweetpotato to nitrogen supply

Nitrogen (N) is an essential element for producing optimum crop yields, but negative responses to high N supply are commonly reported in sweetpotato (Ipomoea batatas) production. This study assessed contrasting responses of sweetpotato yield as a result of N application rates of 0, 30, 60, 90, 130, 160 and 230 kg ha−1 in a glasshouse trial, and rates of 0, 50, 100, 150, 200 and 250 kg ha−1, equivalent to 160, 210, 260, 310, 360 and 410 kg ha−1 when soil N supply is included. The glasshouse-grown sweetpotato produced a maximum number and dry-biomass of storage roots, aboveground biomass and leaf area at 130 kg N ha−1, while leaf N concentration peaked at 90 kg N ha−1. Further increasing N application to 230 kg ha−1 did not result in significant change in any of these attributes. In field-grown sweetpotato, leaf and storage root N concentrations increased with increasing N supply. Although N supply had no effect on the number of storage roots, total yield peaked at 260 kg ha−1. Further increase of N supply reduced the total yield by up to 14% of the maximum yield. With increasing N supply, the glasshouse-grown sweetpotato yield linearly increased with leaf area; the arrangement of the trial permitting light interception to exceed the pot surface area. The yield reduction in field-grown plants was attributed to excess growth of aboveground parts, beyond that needed for efficient light capture. Respirational demand of the aboveground growth occurred at the expense of storage root yields