Influence of photosynthetically active radiation on diurnal N2O emissions under ruminant urine patches

Abstract Nitrous oxide (N2O) is a greenhouse gas and is also recognized as the single most important ozone depleting emission. Static chambers are commonly used to measure N2O fluxes from agricultural soils with fluxes measured over approximately 1 hour typically extrapolated to a daily flux, thus assuming a constant flux over 24 h. Diurnal variation in soil N2O fluxes may lead to inaccurate inventory calculations. The aim of this study was to assess the effect of diurnal changes in photosynthetically active radiation (PAR) on N2O emissions from planted and non-planted soil exposed to bovine urine. The effects of varying PAR, over a 16 h day length, on N2O emissions were observed in a split-split plot factorial experiment conducted in the New Zealand Biotron under constant soil and air temperatures. Treatments included absence or presence of both bovine urine and a 1-month-old perennial ryegrass (Lolium perenne) sward. Diurnal N2O fluxes were determined every 1.5 h on days 6 and 19 after urine deposition ...