Gas flux from a fir bark substrate at an ornamental production nursery

B.J.L. Pitton, X. Zhu-Barker, R.Y. Evans, W.R. Horwath, L.R. Oki
Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) flux from a fir bark substrate was estimated at an ornamental plant nursery in California during a typical 81-day production cycle. The soilless substrate consisted of 4:1 (v:v) fir bark:sand, incorporated with 3.47 kg m‑3 Apex 9-2-0 sulfur-coated urea and 4.51 kg m‑3 Osmocote Plus 15-9-12 controlled release fertilizer. On day zero, Lagerstroemia indica 'Whitt II' plants from number one containers were planted individually into number five containers filled with substrate. On day three, the substrate was topdressed with 34.7 g of 20-9-9 urea-formaldehyde fertilizer. Carbon dioxide and N2O sampling occurred on four days during the first week and once each week thereafter for 14 total sampling days. Methane flux sampling occurred once each week starting on day 18, for nine total sampling days. Eight pots were randomly selected for sampling to measure CO2 and N2O flux and four of these were used to determine CH4 flux as well. Each flux sample consisted of four gas samples taken at 10-min intervals from a static-chamber in each pot and held in Exetainer vials until analyzed by gas chromatography. Gas fluxes were calculated for each pot using the 'gasfluxes' package in R. Mean gas fluxes were -1.5 mg CH4-C m‑2 h‑1, 467 mg CO2-C m‑2 h‑1, and 3.6 mg N2O-N m‑2 h‑1. Low methane concentration in the gas samples and high mean p-value (p=0.24) of methane flux indicated that the CH4 fluxes were negligible. Carbon dioxide and N2O fluxes were highly variable among samples and over the 81-day study. Future work to mitigate greenhouse gases from soilless substrate should focus on N2O emissions since net CH4 flux is negligible and CO2 generated from the fir bark growing media is not considered a greenhouse gas.
Pitton, B.J.L., Zhu-Barker, X., Evans, R.Y., Horwath, W.R. and Oki, L.R. (2021). Gas flux from a fir bark substrate at an ornamental production nursery. Acta Hortic. 1305, 537-544
DOI: 10.17660/ActaHortic.2021.1305.71
fir bark substrate, greenhouse gas, nitrous oxide, methane, carbon dioxide

Acta Horticulturae