Effect of Irrigation on Short-Term Pulses of Greenhouse Gas Fluxes from Manure-Amended Soils.

Greenhouse gas fluxes were monitored at a no-till continuous corn field site contrasting irrigation rates (60% versus 100%), overall nitrogen fertilizer rates (125 versus 200 kg N/ha), and biennial application of cattle feedlot manure.  Greenhouse gas fluxes were assessed after the manure application and after a single irrigation event 4 days after manure application using vented static chambers.  All four treatment combinations receiving fresh manure (60% Irr/125N, 60%Irr/200N, 100% Irr/125N, and 100% Irr/200N) showed enhanced CO₂ fluxes on the day of manure application, but the other gas fluxes (N₂O and CH₄) were unaffected.  Irrigation produced an immediate 5- to 10-fold increase in CO₂ flux from all treatments regardless of manure amendment history (none, 2 years ago, 4 days ago).  Enhanced N₂O irrigation fluxes were also observed for both manure amendments upon irrigation, but CH₄ fluxes were largely unaffected with soils serving as a sink.  For the entire 15-day study period, the integrated N₂O emissions from fresh and old (2 years previously) manured plots were 2.5 to 6 fold higher than no manure plots, with the exception of the 60%Irr/125N treatment that received manure 2 years ago and emitted similarly to no manure plots.  Integrated CO₂ emissions were similar regardless of treatment and manure history.  Soils were a sink for CH₄ except in the 100%Irr/200N treatment where soils released CH₄.