Effect of micro-irrigation type, N-source and mulching on nitrous oxide emissions in a semi-arid climate: An assessment across two years in a Merlot grape vineyard

Micro-irrigation, fertigation, and mulching have been proposed to improve the nutrient and water-use efficiency of crop production. The effect of these management practices on the emission of nitrous oxide (N2O) from vineyards is not well understood and most prior studies were short-term (<1 year). To investigate longer-term effects, a study was conducted in grape (Vitus vinifera L. cv. Merlot planted in a sandy loam soil in British Columbia, Canada. The experiment was a factorial treatment design consisting of two micro-irrigation types (Drip or Micro-sprinkler), two nitrogen sources (surface applied Compost or fertigated Urea at a rate of 40 kg N ha−1), and two vineyard floor managements (bark Mulch or “Clean”-meaning bare soil). Frequent measurements of N2O flux and soil and environmental variables were made over two complete years (2013 and 2014). A considerable portion (37% in 2013 and 61% in 2014) of the annual cumulative N2O emission (ΣN2O) occurred during the pre-growing season particularly within the thaw period. In 2013, the annual area-scaled ΣN2O emissions for Drip was ≈1.8 × Micro-sprinkler, Urea was ≈1.5 × Compost and Clean was ≈1.7 × Mulch. In 2014, ΣN2O emissions were over 14% higher, likely due to more freeze-thaw events, higher soil mineral N availability (47% higher), but treatments differences were not significantly different. Analysed over two years, micro-sprinkler reduced growing season emissions by 29% and surface application of bark mulch decreased annual area-scaled and yield-scaled ΣN2O emissions by 28% and 23%, respectively, suggesting bark mulch as a strategy for mitigating N2O emission. The observed interannual variability in the total N2O emissions suggests that at least a minimum of 2 years of continuous study may be required to estimate representative annual N2O emission budgets and to recommend N2O mitigation strategies in vineyard systems.