Carbon Mineralization in Agricultural Fields II


Project Objective: We wanted to test the ability of the MultispeQ as a tool for measuring soil biological activity. In this project we tested both 'in situ' and 'ex situ' methods for determining soil biological activity in a corn and soybean field in Mason and East Lansing, MI, respectively.

Methods: In each field, we took 3 'in situ' measurements and 3 'ex situ' measurements in the crop row (in row) and between the crop rows (mid row). We took in situ measurements from 4 locations in the test soybean field (3 in corn) and ex situ measurements from 6 locations (5 in corn). We used the 'soil biological activity (5 minutes)' protocol.


Figure 1

For the in situ measurements:

  1. Identify a level spot
  2. Clear all vegetative materials from the sampling area
  3. Insert your soil chamber 1 inch into the soil
  4. Place the MultispeQ into the chamber
  5. Answer all user questions
  6. Close chamber
  7. Start your measurement

For the ex situ measurements:

  1. Weigh out 150-200g of field moist soil (from the upper 0-5 cm of soil), record the weight
  2. Place the soil in the bottom of your canister
  3. Place MultispeQ in canister over top of the soil
  4. Answer all of the user questions
  5. Close the canister
  6. Start your measurement

After each measurement, we calculated the CO2 response curve and used the slope of the line as the CO2 flux rate (kg C ha-1 day-1 for in situ measurements and mg C kg soil-1 day-1 for ex situ measurements). Example response curves are presented in Figure 1.

Figure 2

Results: The CO2 response curves were not always very linear, making it difficult to determine CO2 flux (Figure 1). However, in the corn field we were able to see significant differences between in row and mid row measurements for the in situ measurement. In the crop row, we would expect that increased biological activity in the rhizosphere, root respiration, and banding of fertilizer in the crop row would increase soil biological activity compared to between crop rows. Conversely, in the soybean field, the CO2 flux rates were similar between in row and mid row measurements for both in situ and ex situ measurements.

While it may be possible to measure soil biological activity with the CO2 sensor present in the MultispeQ device, the results from this test suggest better methods need to be developed. One key constraint is the size of chamber necessary to fit the MultispeQ device. A smaller chamber alone may increase the CO2 response curves.

Figure 3