The greenhouse gas (GHG) nitrous oxide (N2O) is produced by soil microorganisms. Nitrogen (N) inputs, soil moisture and carbon stimulate the production of this gas, which accounts for about one third of all GHGs from California’s agriculture sector. Nitrogen inputs, crop N removal, and cumulative N2O emissions were measured from spring 2011 to fall 2012 in three dairy forage production systems receiving liquid and solid manure, as well as synthetic N fertilizer. The annual N2O emissions ranged from 4.8–7.4 kg N2O-N (mass of N in the form of N2O) ha-1 from sites with sandy soil ( > 70% sand) and from 11.4–16.5 kg N2O-N ha-1 in clay soils ( > 40% clay) and were comparable to those of similar systems in other regions (1.2–13.8 kg N loss as N2O) although the California systems received higher N inputs (694-1281 kg N ha-1) than those systems (150–225 kg N ha-1). The periods of N2O release after irrigation events were longer (weeks) in a clayey than in sandy soils (days). Nitrous oxide fluxes up to 1.4 kg N2O-N ha-1 d-1 were recorded after large applications of synthetic N fertilizer ( > 100 kg N ha-1) whereas moderate additions of liquid manure and/or synthetic N fertilizer supplied together with the irrigation water resulted in lower, albeit consistent, N2O emissions of up to 100 g N2O-N ha-1 d-1. To lower N2O emission potential, applying N incrementally in moderate doses with the irrigation water according to crop N demand is recommended.
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