Greenhouse gas emissions from the energy crop oilseed rape ( Brassica napus ); the role of photosynthetically active radiation in diurnal N 2 O flux variation

摘要

Oilseed rape (OSR, Brassica napus L.) is an important feedstock for biodiesel; hence, carbon dioxide (CO 2 ), methane (CH 4 ) and particularly fertilizer?￠????derived nitrous oxide (N 2 O) emissions during cultivation must be quantified to assess putative greenhouse gas (GHG) savings, thus creating an urgent and increasing need for such data. Substrates of nitrification [ammonium (NH 4 )] and denitrification [nitrate (NO 3 )], the predominant N 2 O production pathways, were supplied separately and in combination to OSR in a UK field trial aiming to: (i) produce an accurate GHG budget of fertilizer application; (ii) characterize short?￠???? to medium?￠????term variation in GHG fluxes; (iii) establish the processes driving N 2 O emission. Three treatments were applied twice, 1????week apart: ammonium nitrate fertilizer (NH 4 NO 3 , 69????kg?￠????N????ha ?￠????1 ) mimicking the farm management, ammonium chloride (NH 4 Cl, 34.4????kg?￠????N????ha ?￠????1 ) and sodium nitrate (NaNO 3 , 34.6????kg?￠????N????ha ?￠????1 ). We deployed SkyLine2D for the very first time, a novel automated chamber system to measure CO 2, CH 4 and N 2 O fluxes at unprecedented high temporal and spatial resolution from OSR. During 3????weeks following the fertilizer application, CH 4 fluxes were negligible, but all treatments were a net sink for CO 2 (ca. 100????g CO 2 ????m ?￠????2 ). Cumulative N 2 O emissions (ca. 120????g CO 2 ?￠????eq m ?￠????2 ) from NH 4 NO 3 were significantly greater ( P ????