Oxygen, essential element in the growth of the chicory, is supplied by nutritive solution on top of each pile. The maximum possible oxygen concentration is 8 to 10 mg/l.
The oxygen concentration depends on temperature : the higher the temperature rise,the lower the dissolved oxygen in water gets. At 19°, the maximum dissolution of oxygen is 9 mg/l
With a difficult batch, a vat takes between 1 and 1,5 mg of oxygen and this for a flow of 8 l/mn.
So oxygen is getting rare as we get down in the pile. Consequently oxygen will gradually rarefy when going down into the pile.

Presence of nitrate (NO2) into the nutritive solution is due to the fact that bacteria take the oxygen away from nitrate (NO3). That is starting point of a complicated and unlucky physico-chemical phenomenon, and it is irreversible

The consequence of this downward spiral is, at first, a decelaration and then the stop of the vegetation, and may lead to the loss of the crops. It is just for these reasons that degradation always start from the bottom before getting spread all over the pile and by then contaminating all of the vat.