Nitrous Oxide Emissions From a Norwegian Grassland Following the Application of Mineral and Organic Fertilizer.

Grasslands are an important source of N2O because they receive mineral nitrogen (N) fertilizer and animal manure during the growing season, and legumes are present. The only study on N2O emissions from fertilized grasslands in Norway was performed in 1993 and indicated values up to 3.58 kg N2O-N ha-1. The objective of this work was to quantify N2O emission from a Norwegian grassland following N fertilization and to relate seasonal variations in N2O emissions to soil properties (water content, mineral N concentration). This study was conducted in 2009 in a mixed-species grassland in More and Romsdal county in Western Norway. Two fertilizers sources, ammonium nitrate (AN) and cattle slurry (CS), were applied singly or together on grassland plots (2 m x 8 m) at the following rates: 0, 100, 150, 200 and 250 kg N ha-1 of AN, 80 kg N ha-1 of CS and 200 kg N ha-1 of AN plus 80 kg N ha-1 of CS (200+80). The CS was applied in April and the AN application was split, with one-half applied in April and the remainder applied in June. A permanent collar (54 cm x 54 cm) was inserted at a depth of 10 cm in each plot, gas samples were collected weekly from April to October using the closed chamber method and hourly fluxes were calculated (µg N2O-N m-2 h-1). Cumulative fluxes ranged from 1.5 to 2.1 kg N2O-N ha-1 for the 0 kg N ha-1 (control) and 200 kg N ha-1 treatments, respectively. The N2O cumulative fluxes were significantly (P<0.05) greater from the 150, 200, 250 and 200+80 kg N ha-1 treatments than the control. Soil water content did not exceed 65% water filled pore space during the study, suggesting that N2O production was from nitrification rather than denitrification. These results suggest that higher N fertilizer rates increased N2O emissions, regardless of the fertilizer source, under the field conditions encountered during this study year.