Handheld soil respiration measurements

Growing season soil CO~2~ fluxes are measured at respiration collars using the Li-Cor 6400 and a handheld soil respiration chamber (LiCor 6400-09).

In use at:

Collar installation

PVC collars are inserted in the soil at field sites to make soil respiration measurements with the LI-6400. Collars should be made from ~4 inch (10cm) PVC tubing to accommodate the 9.55cm diameter LiCor-6400-09 chamber. The tubing should be cut at roughly 5cm lengths and then beveled on one edge. These are inserted 1.5-3cm into the soil surface in the location where respiration is to be measured. Because installation of the collars severs roots and upsets the CO~2~ gradient, they should be installed at least 12 hours prior to measurement.

Measurement Procedures

Materials checklist

  • LiCor 6400 (in carrying case)
  • LiCor 6400-09 handheld soil CO~2~ flux chamber (attaches to the IRGA)
  • Cables/tubing for connecting items 1 and 2 (in carrying case)
  • 2 fully charged LiCor batteries
  • 2 full charged spare batteries
  • Pack frame for carrying the case (if hiking into the field)
  • Soil temperature probe (Omega Type-T thermocouple probe) assuming the LiCor 6400's is broken as usual.
  • Bring the probe AND its console
  • Notebook
  • Pen
  • Span gas tank - optional, see the notes in the measurement procedure.

Making measurements with the LI-6400

The general procedure for operating the LiCor 6400 is on the instrument page.

  • This procedure will need to be adapted for each site (see below and notes on the instrument page)

General site considerations

  • Number and location of collars
  • Depends on the site
  • Moving collars
  • Collars may remain stationary through the growing season, or they can be moved prior to each measurement.
    • This depends on research objectives.
  • Allow 12+ hours of recovery after hammering collars in at a new location.
  • Measurement frequency:
  • Every two weeks during the growing season is excellent
  • Less frequently during shoulder seasons?
  • Time of measurements:
  • Morning might be cold
  • Afternoons might be too hot
  • Night might exclude autotrophic components
  • Timing should probably be similar between measurement periods
  • Order of collar measurement:
  • If measuring a control and treatment plot, alternate the measurements so that soil temperature changes during the measurement period occur evenly between treatments.

Notes for Hidden Canyon

  • Typical Aux OP Parameters:
  • Extra drawdown = 5ppm
  • Flow = 500
  • Dead time = 20 sec
  • Minimum measurement time = 30 seconds
  • Delta of around 5-6 usually works best, more if there are lots of roots.
  • May need to modify things to stay within Target +/- Delta range.
  • Measure the soil temperature at 5cm and 15cm depths using the Omega probe (the Li-Cor one is busted)