Test: New soil CO2 testing assembly


Project Objective: This project tests a new soil chamber prototype as a tool for measuring soil biological activity (picture). This new chamber is a 'stand alone' device with a CO2 sensor integrated into the chamber and the chamber is much smaller (10 cm diameter by 6 cm height) than chambers used in previous soil biological activity tests (http://photosynq.org/projects/carbon-mineralization-in-agricultural-fields-ii/)

New Soil Respiration Chamber

Methods: In one corn field and one soybean field, we took measurements from multiple locations. In each location, we took 3 'in situ' measurements in the crop row (in row) and between the crop rows (mid row). We used the 'CO2 evolution without temp/rH' protocol. Before each measurement we identified a level area of ground and removed all vegetative matter from the sample area. We inserted the new soil chamber in the ground 1 cm. We calculated the CO2 response curve and used the slope of the line as the CO2 flux rate (kg C ha-1 day-1). An example response curves are presented in Figure 1.

Figure 1

Results: While we used a 5 minute measurement, we wanted to determine the minimal time necessary to get consistent results. Due to the slow response of the CO2 sensor used in the chamber, we determined that the most consistent linear curves occurred from 65-180 seconds (orange in Figure 1). While not shown here, the results from the 5 minute CO2 curve did not vary significantly from using just a 2 minute slice of the response curve. There were differences in C flux from in row and mid row measurements and differences between corn and soybean fields (Figure 2). These results suggest that the chamber is sensitive enough to pick up differences in soil C flux.

Overall, this new soil chamber appears to be more accurate than using previous methods that involved putting a MultispeQ into a larger chamber over the soil. Furthermore, we think that we can cut the measurement time down to 3 minutes. With a CO2 sensor with a faster response time, it may be possible to reduce the measurement time even more.

Figure 2