Spatiotemporal variation of event related N₂O and CH₄ emissions during fertigation in a California almond orchard

Abstract

Abstract. Nitrogen fertilizer applied to soil is the primary source of the greenhouse gas (GHG) nitrous oxide (N 2 O). The assessment of N 2 O emissions, or net fluxes of the GHG methane (CH 4 ), 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 N 2 O emissions and net CH 4 fluxes (the sum of methanogenic and methanotrophic activity). In this study we examined soil N 2 O-N emissions and net CH 4 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 N 2 O and CH 4 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 N 2 O fluxes were similar to the emitter water distribution pattern and independent of temperature and fertilizer N form applied. Net CH 4 fluxes were extremely low and there was no discernible spatial pattern, but areas kept dry (driveways between tree rows) generally consumed CH 4 while it was produced in the microirrigation wet-up area. The N 2 O-N emissions for fertigation events at the scale of days, and over a season, were significantly higher from the drip irrigated orchard (1.6 6 0.7 kg N 2 O-N ha À1 yr À1) than a microsprinkler irrigated orchard (0.6 6 0.3 kg N 2 O-N ha À1 yr À1 ). N 2 O emissions and net CH 4 fluxes were only significantly correlated with soil water filled pore space and not with mineral-N. The correlation was much better for N 2 O emissions. Our results greatly improve our ability to scale N 2 O production to the orchard level, and provide growers with a tool for lowering almond orchard carbon and nitrogen footprints.

Effects of N Fertilizer Application on Soil N2O Emissions and CH4 Uptake: A Two-Year Study in an Apple Orchard in Eastern China

“…However, the impact of intensive N management on N 2 O and CH 4 fluxes in upland orchards is not well understood because quantitative information on this topic is scarce. Reported N 2 O emissions from orchard soils range from 0.5 to 8.6 kg N ha −1 year −1 and vary in response to climate, land use, and management practices [14,[31][32][33][34][35]. These observations are similar to most cropland-related N 2 O emissions reviewed in Stehfest and Bouwman [20].…”

Irrigation practices, nutrient applications, and mulches affect soil nutrient dynamics in a young Merlot (Vitis viniferaL.) vineyard

“…Several recent studies conducted in orchard systems have also reported that concentrations of extractable NO 3 tend to be higher in soils under drip than microsprinker irrigation (Alsina et al 2013; Kadyampakeni **** ** **** **** **** I × A n s n s n s n s n s…”

“…Webb) orchard suggests that differences in NO 3 -N IER between irrigation treatments are not caused by losses of mineral N via denitrification (Alsina et al 2013). Instead, greater water-filled pore spaces in the wetted bulb of soil beneath drippers may support higher rates of N mineralisation; under microsprinklers, higher evaporative losses from the soil surface tend to reduce soil moisture, which may lead to lower rates of N mineralisation (Alsina et al 2013). Furthermore, uniformly wet conditions, as were observed under drip irrigation, may support greater rates of cumulative N mineralization than repeated drying-wetting cycles (Mikha et al 2005).…”

“…1). Given that NO 3 leaching losses and N 2 O emissions are driven largely by soil moisture dynamics Alsina et al 2013;Vallejo et al 2014), future work is required to characterise soil microclimatic conditions across the plot surface and deeper into the soil profile to better understand how micro-irrigation practices affect soil N mineralisation and loss.…”

“…three emitters in each plot, perpendicular to the vine row. Sampling was restricted to the wetted zone of surface (5-15 cm) soils, located approximately 30 cm from both emitter types, because this region tends to be a focal point for nutrient leaching losses (Neilsen et al 2000 and greenhouse gas emissions (e.g., nitrous oxide; Alsina et al 2013;Vallejo et al 2014). During installation of the resins, a slit was made with a trowel to a depth of approximately 15 cm; the resin strip was inserted vertically into the slit and the soil was then repacked around the strip to ensure contact between the soil and the resin strip.…”