Seasonal Variability of Nitrous Oxide Emissions From Two Nitrogen Sources In a California Almond Orchard.

Application of nitrogen (N) fertilizers by agriculture contributes to the increase of the greenhouse gas, nitrous oxide (N₂O), in the atmosphere.  Multiple stakeholder groups in California share a similar goal of constraining N₂O emissions.  Both temporal and spatial variation as well as N fertilizer source confounds accurate prediction of N₂O emissions across diverse landscapes of perennial crops like almond (Prunus dulcis).  During seasonal applications of N fertilizer, different amounts of time elapsed before peak N₂O emissions.  These results suggested the combined role of temperature and water-filled pore space as drivers of N₂O emissions after fertilization.  Furthermore, spatial variation of N₂O emissions can be explained both by fertilizer and water distribution from fanjet irrigation in addition to the practices of using raised berms in tree rows.  During sampling of peak emissions, our results indicated significant treatment differences (p < 0.0001) between two N fertilizer sources, urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN).  Different concentrations of ammonium (NH₄⁺) and nitrate (NO₃^-) in the fertilizer sources and subsequent NH₄⁺ and NO₃^- availability in the soil environment may explain the extent of microbial nitrification and denitrification to emit different amounts of N₂O.  Our work will further identify management strategies to mitigate the effects of N₂O emissions during N fertilization.