Department of Agricultural Engineering (Institut für Landtechnik), University of Bonn, Germany

Making silage involves a complicated biochemical process. Monitoring the depletion process of oxygen in the ensiling/initial aerobic phase can provide critical information to identify when the anaerobic fermentation essentially starts, but in situ data of exhibiting this process remains rare.


The crop harvested for making silage was whole maize that were finely chopped and then packed into six glass jars (1.5 L). Of them three were jars packed with a high wet bulk density (H-WBD) (800 kg m-3) and the other jars were packed to a lower wet bulk density (L-WBD) (520 kg m-3). Regarding sensor installation, (i) to push a screwdriver (diameter: 3 mm) into the center of the chopped maize (FIG. 1A) until the depth of 8 cm and then (ii) to pull it out so that an undersized hole was left in the material to be measured; (iii) an oxygen probe (OXROBSC, PyroScience, Germany) together with its cable passed through a rubber stopper that was fixed on a PVC lid (FIG.1B); (iv) the probe was inserted into the undersized hole of the material and (v) the jar was sealed by the lid using four metallic clips (FIG. 1C).


Two time-courses (FIG. 2), each represented the mean of triple replications, were recorded from the oxygen depletion process in the experiment. The initial aerobic phase was completed and anaerobic fermentation started when the oxygen concentration reached zero. The consumption process of oxygen (red) in the H-WBD jars was significantly faster (approx. 1.5 h) than that (blue) of L-WBD (approx. 2 h). This is because the H-WBD was not only equal to having a low level of porous volume for oxygen, but also related to having a relatively large number of plant cells respiring in the jars. The situation for the L-WBD was opposite.


The data demonstrate that the oxygen sensor evaluated is preferred for our silage research. Two major advantages are highlighted: (i) unlike electrochemical oxygen sensors, this fiber-optic oxygen sensor does not consume oxygen (analyte) during measurement, i.e., avoiding competition to local microbial consumption in the substrate; (ii) the tiny size of the probe allows to be used for small silage samples, such as the 1.5L-jar.

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