Regulation of nitrous oxide emissions from soils irrigated with dairy farm effluent

Animal slurries and effluents are commonly applied to soil as a source of organic N fertilizer. By increasing inorganic N, applying animal effluents may also increase soil nitrous oxide (N2O) emissions. Our objectives were to (i) determine if dairy farm effluent (DFE) irrigation increased short-term N2O emissions from a surface-drained peat soil and a freely drained mineral soil and (ii) see if this increase could be attributed to increased N availability, increased soil water content, or a combination of both factors. We measured short-term N2O emissions following DFE irrigation in spring and autumn, using closed chambers. Nitrous oxide emissions from DFE-irrigated soils (50 kg N ha(-1), 20-mm hydraulic loading) were compared with soils receiving inorganic nitrogen and water (50 kg N ha(-1), 20 mm), inorganic N only (50 kg N ha(-1)), water only (20 mm), and no treatment. Nitrous oxide emissions increased immediately following DFE irrigation to both soils, and were generally greater than emissions following the application of inorganic fertilizer with water. Increased N20 emissions following DFE irrigation coincided with increased soil water contents and mineral N and CO2 emissions. We suggest that DFE application increased N2O emissions more than inorganic N fertilizer by enhancing denitrification either by increasing C availability and/ or decreasing soil aeration following increased respiration. These findings suggest that the proportion of N applied to the soil and emitted as N2O may at times be greater for organic N fertilizers than inorganic N fertilizers, particularly if the organic N fertilizer contains sufficient available C to enhance denitrification.