Greenhouse Gas Emission and Redox Potential in Biochar- and Compost-Amended Urban Soil Under Contrasting Water Saturation Conditions
Angel Salinas1, Maximiliano Bettini1, Ana Casillas1, Edgar Garcia1, James Kang1* (firstname.lastname@example.org), Chu-Lin Cheng1,2, Engil Pereira1, Rafael Almeida1
1School of Earth, Environmental, and Marine Sciences, University of Texas Rio Grande Valley, Edinburg, TX; 2Department of Civil Engineering, University of Texas Rio Grande Valley, Edinburg, TX
Soils are significant sources and sinks for greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). There have been many studies investigating GHG dynamics in agricultural soils but there have been limited studies for urban soils. This project was designed to investigate urban soil GHG emissions affected by soil hydrologic conditions, organic soil amendments (biochar and/or compost), and redox chemistry through soil mesocosm experiment. The soil material was a compost-soil blend that is sold from the City of McAllen, TX, representing a typical urban gardening soil. The soil was packed into a total of 12 columns (5-gallon buckets) at a bulk density of 1.1 g cm-3. The treatment consisted of four amendment treatments for biochar, compost, biochar + compost, and no amendment as control) and the amendments were surface-applied at 5-cm thickness. Grass sod (Saint Augustine) was placed on the top of the amendment with surface application of 14-14-14 (N-P-K) fertilizer. The amendments were considered as subplots and each subplot will receive repeated wetting-drying cycle at full saturation, half-saturation, or unsaturated condition up to 8 weeks. For instance, the full-saturation treatment will be held for the first 2 weeks and will be drained for the next 2 weeks (unsaturated) and this 4-week cycle will be repeated twice. Each soil column will be instrumented with redox probes (SWAP instrument, Inc., Netherland) that measures redox potential (Eh in millivolt) by 10-cm increment. Soil moisture will be measured manually using a commercial soil moisture probe (up to 15 cm deep). GHG measurements will be done through LI-COR soil gas flux survey chamber equipped with CO2/CH4 trace gas analyzer (LI-7810) and N2O trace gas analyzer (LI-7820). Currently, preliminary testing for redox probes under various water table conditions and background GHG emission measurements are in progress. The presentation will present the first-round of soil mesocosm experiment results along with physicochemical characterization of the amendments and soil material.