Nutrient Management Research Database

Nitrogen fertilizer applied to soil is the primary source of the greenhouse gas (GHG) nitrous oxide (N2O). The assessment of N2O emissions, or net fluxes of the GHG methane (CH4), are lacking for upland, arid agricultural ecosystems worldwide. In California, where rates of application for nitrogen (N) can exceed 300 kg per hectare for N-intensive fruit and nut crops (.2 million acres), liquid N fertilizers applied through microirrigation systems (fertigation) represent the predominant method of N fertilization.
Little information is available for how these concentrated and spatially discrete N solution applications influence N2O emissions and net CH4 fluxes (the sum of methanogenic and methanotrophic activity). In this study we examined soil N2O-N emissions and net CH4 fluxes for drip and stationary microsprinklers, two of the most widely used fertigation emitters, in an almond orchard where 235.5 kg N/ha were applied during the season of measurement (2009–2010). We accomplished this by modeling the spatial patterns of
N2O and CH4 at the scale of meters and centimeters using simple mathematical approaches. For two applications of 33.6 kg/ha and three applications of 56.1 kg/ha targeted to the phenologic stages with highest tree N demand, the spatial patterns of N2O fluxes were similar to the emitter water distribution pattern and independent of temperature and fertilizer N form applied. Net CH4 fluxes were extremely low
and there was no discernible spatial pattern, but areas kept dry (driveways between tree rows) generally consumed CH4 while it was produced in the microirrigation wet-up area. The N2O-N emissions for fertigation events at the scale of days, and over a season, were significantly higher from the drip irrigated orchard (1.6 +- 0.7 kg N2O-N ha1yr^-1) than a microsprinkler irrigated orchard (0.6 +- 0.3 kg N2O-N ha1 yr^-1). N2O emissions and net CH4 fluxes were only significantly correlated with soil water filled pore space and not with mineral-N. The correlation was much better for N2O emissions. Our results greatly improve our ability to scale N2O production to the orchard level, and provide growers with a tool for lowering almond orchard carbon and nitrogen footprints.

This study was conducted during 2009-2010 near Arbuckle, California in an almond orchard with 19 year old trees.

• Trees were oriented N to S with 6.7m between rows and 4.9m spacing between trees within rows.
• The experiment was set up in a randomized 3 block design with one single line drip irrigation treatment and one stationary microsprinkler treatment in each block.
• A total of 235.5 kg of N was applied and split between 5 fertigation events, corresponding to phenological stages corresponding with high N demand.
•  In each treatment replicate, one tree was randomly chosen and 10 chamber positions were chosen to measure N20 and CH4 soil fluxes.
• Gas fluxes were measured on the day of fertigation, for the three days afterward, and then every two days, and finally every seven days as emissions decreased to baseline rates. Fluxes were measured every 1-2 weeks between fertigations.
• Soil samples were taken after each time gas fluxes were measured and analyzed for water filled pore space, extractable soil ammonium and nitrate concentrations

• For all but one fertigation event, N20 emissions were significantly higher than emissions from microsprinkler fertigation.
• N20 emissions increased in association with water filled pore space for both treatments.
• CH4 flux was small and variable, with no difference between fertigation treatments
• Results suggest that using different fertigation frequencies or minimizing the application of N during the warm season could help reduce N20 emissions under drip irrigation.