A low cost multi-chamber system (“Greenhouse Coffins”) to monitor CO2 and ET fluxes under semi-controlled conditions: Design and first results

Determining greenhouse gas (GHG) fluxes, water (ET) fluxes and their interconnectivity within the soil-plant-atmosphere-intersphere is crucial, not only when aiming to find solutions for current agricultural systems to mitigate the global climate crises but also to adapt them to related challenges ahead, such as more frequent and severe droughts. In a first attempt for a better understanding, often laboratory and/or greenhouse pot experiments are performed, during which gas exchange is predominately measured using especially manual closed chamber systems. Commercially available systems to determine gas exchange in terms of CO₂ and ET are, however, costly and measurements itself labour-intensive. This limits the amounts of variables to be studied as well as possible repetitions during a study. Additionally, it resulted in the long-term focus on agroecosystems of the northern hemisphere while agroecosystems of sub-Saharan Africa as well as Southeast Asia are still being underrepresented.

We present an inexpensive (<1.000 Euro), Arduino based, multi-chamber system to semi-automatically measure 1) CO₂ and 2.) ET fluxes. The systems consists of multiple, self-sufficient, closet-shaped PVC “coffins”. The “coffins” a closed by a frontal door and periodically ventilated through a sliding window. Relays connected to the microcontroller are used to steer closure/opening (linear actuator) and ventilation (axial fans). CO₂ and ET fluxes are determined through the respective concentration increase during closure by a low-cost NDIR CO­₂ (K30FR; 0-10,000 ppm, ± 30 ppm accuracy) and rH sensor (SHT-41). Parallel measurements of relevant environmental parameters inside and outside the “coffins” are conducted by DS18B20 (temperature) and BMP280 (air pressure) sensors. Sensor control, data visualization and storage, as well as steering closure/opening and ventilation is implemented in terms of a wifi and bluetooth enabled, socket powered (9V), compact microcontroller (D1 RS32) based logger unit. Here, we present the design, and first results of the developed, low-cost multi-chamber system. Results were validated against results of customized CO2 and ET measurement systems using regular scientific sensors (LI-COR 850) and data logger components (CR1000), connected to each “coffin” by a multiplexer.  Flow-meter were used for measurement synchronization.