SOIL AND PLANT ANALYSIS (1+1)

Oxygen diffusion meter

The oxygen diffusion meter(i,ii,iii) measures the mobility of oxygen in the soil that is important for the availability of oxygen for plants.

The method: measuring the electric current required for the reduction of all oxygen present at the surface of a cylindrical Pt-electrode in the soil. The flow of oxygen through the air-filled pores and the water film on the electrode is measured until the steady state is reached.

The Oxygen Diffusion Rate (ODR) probe (Pt-electrode) should be placed in undisturbed soil. To this purpose a hole is predrilled to a depth of approximately 10 mm above the measuring point, after which the probe is lowered and carefully pushed into the bottom of the auger-hole. It is advised to remove the electrode from the soil after a series of measurements in order to clean it. The meter provides a stabilized voltage between the ODR-probe and the Ag-AgCl-reference electrode.

In very dry soils only part of the electrode will be covered in water. This results in rising impedance between soil and electrode. In such a situation the meter can also be used to perform a redox-potential measurement.

The measuring system consists of a read-out unit with connecting facilities for three ODR-probes, one ODR-probe, one Ag-AgCl reference electrode, KCl-solution and a brass electrode. The reference electrode is used for measuring and checking the potential between the Pt-electrode and the soil. The brass electrode is used to close the electrical circuit. The measuring range for oxygen diffusion is 0 - 999 μA and for Redox 0 - 999 mV (resolution resp. 1 μA and 1 mV). Accuracy +/- 3 μA and +/- 3 mV. Operating temperature between 0 and 50°C and an air humidity between 30 - 80%.