Effects of aggregate size, soil compaction, and bovine urine on N2O emissions from a pasture soil

Abstract The dominant N 2 O emission source in New Zealand, calculated using the Intergovernmental Panel on Climate Change methodology, is agricultural soils. The largest source of N 2 O emissions in New Zealand occurs as a result of excreta deposition onto pasture during grazing. There is a dearth of studies examining the effect of soil compaction and soil aggregate size on N 2 O emissions from urine patches in grazed pastures. In this study, we repacked soil cores with four different soil aggregate sizes ( 2 O were monitored for 37 days after which soil cores were allowed to dry out prior to a rewetting event. There was an interaction between aggregate size and soil compaction with the cumulative loss of N 2 O over the first 37 days ranging from 0.3% to 9.6% of the urine-N applied. The highest N 2 O emissions occurred from the smallest and most compacted aggregates. Even under the highest levels of compaction the N 2 O loss from the large aggregates (4.0–5.6 mm diameter) was 2 O flux from the different-sized aggregates included varying gas diffusivities and higher rates of denitrification in the smallest aggregates, as evidenced by the disappearance of nitrate.