Urea-induced nitrous oxide emissions in multi-species swards: effect of clover species and density
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- Master's theses (IPM) 
Abstract Grazed grasslands have been identified as an important source of anthropogenic nitrous oxide (N2O) emissions. The loss of soil N as N2O is a critical factor for managing sustainable agroecosystems, not only with respect to the contribution of N2O to global warming by radiative forcing, but also for its effect on stratospheric ozone depletion. An experiment was set up on the experimental farm Østervoll, SE Norway, to investigate the effect of clover density in multi species swards (MSS) on N2O emissions from urine patches. The species used in the MMS were ryegrass, tall fescue, red clover and white clover. Clover densities ranged from 0-100% in mixed stands with grass yielding all together nine different treatments. We used artificial urine (50 g N m-2) to simulate urine deposition and measured N2O flux using static chambers. Gas samples were analyzed by gas chromatography and soil samples were analyzed for NH4+ and NO3-. Harvest took place on the 13th of September and the plant samples were analyzed for N yield and clover percentage. The data obtained were analyzed using one way ANOVA. The results showed no significant differences in cumulative N2O emission in the period from urea application to ley harvest between grass treatments and grass dominated mixtures, however high emissions were associated with clover monocultures. The high standard error within replicates of the same treatments suggested an effect of topography, resulting in lower emissions in plots situated on a slope, presumably because of nitrogen leaching. When scaled for N-yield, cumulative N2O emissions tended to be higher for treatments with high clover percentage. In conclusion, clover percentage and species distribution had little effect on urine-associated N2O emissions. This warrants that there might be tradeoff between increasing N uptake by companion grass and N yield-scaled N2O emissions in grazed multispecies pastures.