Nutrient Management Research Database

Environmental conditions and agricultural management events affect the availability of substrates and microbial habitat required for the production and consumption of nitrous oxide (N2O), influencing the temporal and spatial variability of N2O fluxes from soil. In this study, we monitored for diurnal and event-related patterns in N2O emissions in the field, evaluated how substrate availability influenced denitrification, and assessed N2O 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 N2 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 N2O emissions. The lack of consistent diurnal patterns also indicates that measuring N2O emissions once per day following major events is sufficient to adequately assess annual N2O emissions in those systems. Nitrous oxide emissions varied per event and across functional locations in both systems. This illustrates that mechanisms underlying N2O emissions vary at relatively small temporal and spatial scales and demonstrates the importance of studying N2O emissions in the context of events and functional locations. In the conventional system, N2O fluxes were high [74.2 +/- 43.9–390.5 +/- 90.1 μg N2O-N m2 h2] and N2O 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 N2O 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 N2O reduction.

• This study compared the effects of a conventional tomato cropping system, which utitilized two sidedress applications of CAN17 with furrow irrigation and standard tillage, to an integrated system with buried drip lines used for fertigation of UN-32 along with reduced tillage.
• Nitrous oxide emissions, ammonium and nitrate, and soil moisture content along the furrow, shoulder, and bed were monitored over the course of a cropping season.

Some important findings from this study:

• Emissions in the integrated system were over 80% lower than the conventional system.
• Conditions favoring denitrification were observed in the conventional, furrow irrigated system, while these conditions were not observed in the integrated system utilizing buried driplines.
• Soil nitrogen levels were highest in the furrow and shoulder in the conventional system, while they were highest in the berm for the integrated system.