Spatial and temporal variability of nitrous oxide emissions in a mixed farming landscape of Denmark

Abstract

Nitrous oxide (N₂O) emissions from agricultural land are variable at the landscape scale due to variability in land use, management, soil type, and topography. A field experiment was carried out in a typical mixed farming landscape in Denmark, to investigate the main drivers of variations in N₂O emissions, measured using static chambers. Measurements were made over a period of 20 months, and sampling was intensified during two weeks in spring 2009 when chambers were installed at ten locations or fields to cover different crops and topography and slurry was applied to three of the fields. N₂O emissions during spring 2009 were relatively low, with maximum values below 20 ng N m⁻² s⁻¹. This applied to all land use types including winter grain crops, grasslands, meadows, and wetlands. Slurry application to wheat fields resulted in short-lived two-fold increases in emissions. The moderate N₂O fluxes and their moderate response to slurry application were attributed to dry soil conditions due to the absence of rain during the four previous weeks. Cumulative annual emissions from two arable fields that were both fertilized with mineral fertilizer and manure were large (17 kg N₂O-N ha⁻¹ yr⁻¹ and 5.5 kg N₂O-N ha⁻¹ yr⁻¹) during the previous year when soil water conditions were favourable for N₂O production during the first month following fertilizer application. Our findings confirm the importance of weather conditions as well as nitrogen management on N₂O fluxes.