Assessing drivers of N2O production in California tomato cropping systems.

Abstract Environmental conditions and agricultural management events affect the availability of substrates and microbial habitat required for the production and consumption of nitrous oxide (N 2 O), influencing the temporal and spatial variability of N 2 O fluxes from soil. In this study, we monitored for diurnal and event-related patterns in N 2 O emissions in the field, evaluated how substrate availability influenced denitrification, and assessed N 2 O reduction potential following major events in two tomato ( Lycopersicon esculentum ) management systems on clay loam soils: 1) conventional (sidedress fertilizer injection, furrow irrigation, and standard tillage) and 2) integrated (fertigation, subsurface drip irrigation, and reduced tillage). Potential denitrification activity, substrate limitation, and reduction to N 2 were measured with an anaerobic slurry technique. In the field, we found no consistent diurnal patterns. This suggests that controlling factors that vary on an event-basis overrode effects of diurnally variable controls on N 2 O emissions. The lack of consistent diurnal patterns also indicates that measuring N 2 O emissions once per day following major events is sufficient to adequately assess annual N 2 O emissions in those systems. Nitrous oxide emissions varied per event and across functional locations in both systems. This illustrates that mechanisms underlying N 2 O emissions vary at relatively small temporal and spatial scales and demonstrates the importance of studying N 2 O emissions in the context of events and functional locations. In the conventional system, N 2 O fluxes were high [74.2 ± 43.9–390.5 ± 90.1 μg N 2 O-N m − 2  h − 1 ] and N 2 O reduction potential was significant. Both management systems exhibited carbon limitation on denitrification rates; and rates were N limited in the third fertigation event in the integrated system. Our findings suggest that denitrification is strongly contributing to high N 2 O emissions in conventional tomato cropping systems in California. Hence, management practices that reduce the conditions that favor denitrification, such as subsurface drip irrigation, are promising strategies for N 2 O reduction.