Contribution of denitrification and ammonia oxidation to nitrous oxide emissions from three organic soilless substrates

Nitrous oxide (N₂O) emissions from soilless growing substrates are significantly greater per production area than crops grown in mineral soil. To understand and identify the N₂O production pathways in soilless substrates, fir bark, peat, and peat:fir bark substrates were treated with labeled ¹⁵N fertilizers. The volumetric water content (VWC) of the soilless substrate was maintained near container capacity, and gas samples were collected every other day for 21 days and analyzed for ¹⁵N-N₂O content. Fir bark and peat:fir bark substrates had significantly greater total N₂O emissions than peat substrate when fertilized with NH₄NO₃. Denitrification was the main pathway of N₂O emissions from all substrates and it was more pronounced in the fir bark and peat:fir bark substrates. In the peat substrate, the contribution of ammonia oxidation to N₂O emissions started on day 11 and continued to increase until the end of the experiment, contributing to 6 % of the total N₂O emitted from this substrate. Overall, reducing denitrification-derived emissions from soilless substrates is critical to mitigate the impact of container-plant production on global warming. Future research should focus on developing strategies to reduce these emissions.