Impact of Compost Tea and Row Management on Orchard Soil Greenhouse Gas Emissions and Soil Properties

By: Clarissa Maciel and Angelica Crecencio

Department: Geography

Faculty Advisors: Dr. Andrew Oliphant, Dr. Leonhard Blesius, and Dr. Sara Baguskas

Agricultural soils produce large amounts of greenhouse gas (GHG) emissions to the atmosphere, particularly carbon dioxide (CO2) in sub-saturated conditions and methane (CH4) in saturated or anoxic conditions. In addition, agricultural soils tend to be significant sources of nitrous oxide (N2O), particularly when nitrogen amendments are used. Given the scale of global agriculture and its greenhouse fingerprint, the impact of different types of soil amendments and management practices on soil GHG emissions has received increasing attention. In this study, we observed daytime soil emissions of CO2, CH4 and N2O in an orchard near Sebastopol California through the growing season of 2021. The experimental design targeted the differences between orchard blocks amended with compost tea and control blocks, as well as differences between row disking, pruning mulch, and no row management. Overall, the orchard soils were found to be a consistent source of CO2 to the atmosphere (2.5 ± 1.3 mg m-2 s-1), a very weak source of N2O (0.17×10-3 ± 0.24×10-3 mg m-2 s-1) and a very weak sink of atmospheric CH4 (-0.9×10-3 ± 0.9×10-3). Although CO2 is the largest mass flux of the three gasses it has the lowest warming potential with CH4 having approximately 25 times and N2O approximately 298 times the CO2 equivalent by mass. Owing to the much larger magnitude, CO2 is still the largest contributor, two orders of magnitude higher than N2O. The absorption of atmospheric CH4 by the orchard soils offset about half of the warming potential of the N2O flux. The fluxes were relatively normally distributed and the distributions varied subtly between compost tea application status and also between row management types. However, relatively few of the differences were statistically significantly different, with the most common significant difference occurring between the no management and the two other management types