Nitrous Oxide Emitted from Soil Receiving Anaerobically Digested Solid Cattle Manure

Limited information is available about soil nitrous oxide (N2O) fluxes, N2O emission factors (EFs), and yield-scaled N2O emissions for biogas residues used to fertilize crops in semiarid regions. To address this knowledge gap, a 4-yr field experiment was conducted in a semiarid climate to determine growing season N2O fluxes from soil receiving (i) anaerobically digested solid beef cattle manure (digestate), (ii) separated solids from the digestate (separated solids), and (iii) undigested solid beef cattle manure (cattle manure) applied to target one and two times the recommended rates (200 and 400 kg total N ha(-1)) for barley (Hordeum vulgare L.) forage, assuming 50% of N was annually plant available. Nitrous oxide fluxes were determined using vented static chambers. Over the four growing seasons, 95, 80, and 81% of the N2O flux occurred within 36 d of applying digestate, separated solids, and cattle manure, respectively. The cumulative N2O emissions with digestate were 4.7 and 4.1 times the values of the separated solids and cattle manure, respectively. The digestate N2O EF was 13.6 and 10.6 times the values of the separated solids and cattle manure, respectively, but the N2O EF based on applied mineral N was similar for all amendments. The yield-scaled N2O emissions with digestate were 4.3 and 3.6 times the values of the separated solids and cattle manure, respectively. In the semiarid region of southern Alberta, liquid biogas residues have a higher risk for N2O emissions than both the separated solid fraction of the biogas residues and undigested cattle manure.