AbstractsPhysics

Micro-irrigation scheduling, fertigation and mulching can be used by growers to improve the nutrient and water-use efficiency of crop production. Agriculture contributes to global warming through emission of greenhouse gases CO₂ N₂O, and CH₄. There is little information about how management practices affect N₂O emissions from vineyard and orchard soils. In a two year field experiment, N₂O fluxes from a grape (Vitis vinifera L.; Merlot) vineyard and an apple (Malus domestica Borkh; Ambrosia) orchard under microirrigation in the semiarid Okanagan Valley of British Columbia were measured using static chambers. Soil mineral N and organic carbon, environmental variables and fruit yield were also monitored. Treatments in the grape vineyard involved micro-irrigation types (Drip or Micro-sprinkler), nitrogen sources (surface-applied compost or fertigated Urea; 40kg N ha‐¹), and two floor managements (surface-applied shredded bark and wood Mulch or Clean - bare soil). Treatments in the apple orchard involved drip irrigation frequency (twice per day or twice per day on every 2nd day) delivering the same total amount of water, orchard floor management (Mulch or Clean) and nitrogen application rate applied as calcium nitrate by fertigation (20 or 40 g N tree‐¹). Spring thaw accounted for 30 to 50% of annual emissions in both experiments. Over a period of two complete years in the grape vineyard Micro-sprinkler irrigation reduced growing season N₂O emissions by 29% (compared to Drip) and on an annual basis Mulch decreased them by 28% (compared to Clean ). In the apple orchard irrigation every 2nd day reduced N₂O emissions by 30% and application of Mulch reduced them by 20%. Reduced drip irrigation frequency and mulching may provide an opportunity for suppressing N₂O emissions from drip-irrigated vineyards and orchards. There was alsolarge spatial variability of N₂O and CO₂ emissions with respect to distance relative to the apple tree and dripper locations. The emission factor (N emitted as N₂O per unit of total applied N) from the applied fertilizer (uncorrected for background emission) across all treatments averaged 2.8% in the vineyard and 2.4% in the orchard. The 1% default IPCC emission factor likely underestimates N₂O emissions from these systems.