Soil Microbial CO2 Respiration Testing, Effect of Partial Pressure

As the need for more sustainable and efficient agricultural operation develops, a more real time and finer grained mapping of the influence of soil quality and composition on crop production and properties is necessary. Few real time tools are available for farmers to profile their soil, particularly on a molecular level, where microbial decomposition synthesizes the nutrients required to grow crops. Thus, this overall research project focuses on the development of wirelessly powered subsurface soil sensors categorizing soil quality by profiling the gaseous byproducts of organic decomposition within the soil. As a subproject, the present report details the qualification of hydrophobic membrane compatibility for passive transport of CO₂ to the sensor chamber. A larger scale prototype has been constructed to test the membrane, which will later be scaled down. The device has been designed and assembled in its initial form in Spring 2023, utilizing an Isco high-pressure syringe pump(s), Matheson flow controllers, and high-pressure steel tubing. Flows of pre-pressurized water and CO₂ were fed from the syringe pump to a high-pressure acrylic vessel while N₂ serves as a countercurrent carrier gas. Early results from pure CO₂ feed in terms of permeability as a function of carrier gas flow will be described.