Nitrous Oxide Emissions from Manure and Inorganic Fertilizers Applied to Spring Barley

Nitrous oxide emissions from soil amended with untreated liquid manure (slurry), anaerobically digested slurry, or inorganic fertilizers (calcium ammonium nitrate or urea) were quantified in a field study covering two growth seasons of spring barley (Hordeum vulgare L.). In the first year incorporation before seeding was compared with trail hose application 5 wk after seeding. In the second year all fertilizers were applied before seeding, while soil moisture and initial NO−3 availability was varied. Accumulated N2O losses between the time of fertilization and ca. 1 July represented 0.14 to 0.35% of total N in 1996 and 0.34 to 0.64% in 1997. In both years the highest N2O emissions were observed with untreated slurry, whereas digested slurry and inorganic fertilizers were at a similar level. Increasing the soil moisture content or NO−3 availability had no significant effect on accumulated N2O losses. Although metabolizable C may thus have stimulated N2O emissions via denitrification from untreated slurry, the largest contribution to N2O fluxes probably came from nitrification with all fertilizer types. Using the IPCC guidelines it was estimated that anaerobic digestion of slurry per se could potentially reduce N2O emissions from Danish agriculture by 1.2 to 2.5%.