An Assessment of Three Different In Situ Oxygen Sensors for Monitoring Silage Production and Storage

Oxygen (O(2)) concentration inside the substrate is an important measurement for silage-research and-practical management. In the laboratory gas chromatography is commonly employed for O(2) measurement. Among sensor-based techniques, accurate and reliable in situ measurement is rare because of high levels of carbon dioxide (CO(2)) generated by the introduction of O(2) in the silage. The presented study focused on assessing three types of commercial O(2) sensors, including Clark oxygen electrodes (COE), galvanic oxygen cell (GOC) sensors and the Dräger chip measurement system (DCMS). Laboratory cross calibration of O(2) versus CO(2) (each 0–15 vol.%) was made for the COE and the GOC sensors. All calibration results verified that O(2) measurements for both sensors were insensitive to CO(2). For the O(2) in situ measurement in silage, all O(2) sensors were first tested in two sealed barrels (diameter 35.7 cm; height: 60 cm) to monitor the O(2) depletion with respect to the ensiling process (Test-A). The second test (Test-B) simulated the silage unloading process by recording the O(2) penetration dynamics in three additional barrels, two covered by dry ice (0.6 kg or 1.2 kg of each) on the top surface and one without. Based on a general comparison of the experimental data, we conclude that each of these in situ sensor monitoring techniques for O(2) concentration in silage exhibit individual advantages and limitations.