Greenhouse Gas Emissions and Global Warming Potential from a Woody Ornamental Production System Using a Soilless Growing Substrate

This research aimed to estimate methane (CH4) and nitrous oxide (N2O) fluxes and subsequent global warming potential (GWP) for a Douglas fir (Pseudotsuga menziesii) bark-based substrate production system. The fir bark-based substrate had controlled release fertilizer (CRF) incorporated with differing amounts of surface-applied fertilizer. In a nursery study and greenhouse experiment, gas flux samples were regularly collected. Total cumulative N2O emissions and GWP were greatest from the greenhouse treatment with the most surface-applied fertilizer. A regression model indicated that significant predictors of N2O flux were the pour-through extract ammonium (NH4-N) and nitrate (NO3-N) concentrations, volumetric water content (VWC), and substrate temperature. The net CH4 flux was negligible for all treatments during both studies. The N2O-N seasonal emission factor was 2.58–3.08, greater than for soil-grown California horticultural crops. These results indicate that N2O is the major greenhouse gas from a soilless substrate and should be the focus of mitigation efforts.