Nitrous Oxide Emission from Micro-Irrigated Grape and Apple Fields Located in the Semi-Arid Okanagan Region of British Columbia.

Many vineyards and orchards have converted from overhead sprinklers to micro-irrigation via under-vine/tree microspray or drip emitters to improve water-use efficiency.  Micro-irrigation combined with various nutrient management practices provides a cost-efficient mechanism to supply water and nutrients. The effect of these management practices on the emission of nitrous oxide is not well understood in woody perennials.  Studies are underway in grape (Vitis vinifera L.; Merlot) planted in a sandy loam soil and apple (Malus domestica Borkh; Braeburn) planted in a loamy sand soil in Summerland, B.C.  The grape plots received 40 kg/ha nitrogen from 1) compost, 2) urea, 3) urea plus high carbon (C) mulch, or 4) compost plus high C mulch, and are either drip or microspray irrigated four times a day.  Results of the first full year of the two year experiment indicate significant effects of irrigation type, N-source, and surface management.  Emissions during spring thaw and the growing season were 28%/69% respectively for microspray and 44%/56% for drip irrigation.  Area-scaled (kg N/ha) and yield-scaled (kg N/kg grapes) cumulative annual emissions were Spray< Drip, Compost<Urea, and Mulch<No Mulch in grape plots.  The apple site data suggests that the effect of mulch may vary for crop and age of mulch.  Two years long term GHG monitoring data and the corresponding fruit production data will be utilized to recommend the best management practices.