The air humidity (or relative humidity) expresses the saturation of the air with water vapour as a percentage.
In fact, the air can only hold a limited amount of water vapour. If humidity is at 100%, no more water can be stored in the air in gaseous form, meaning that some of it becomes liquid, forming dew.
It is useful to know the humidity level for a number of reasons:
- The right humidity is a prerequisite for the efficacy of phytosanitary treatments. A humidity level above 60% limits evaporation and maximises absorption of the active ingredient by the plants.
- In combination with the wet bulb temperature, humidity is a useful piece of data in preventing freezing, as it helps farmers to anticipate drops in temperature (see article What is the wet bulb temperature?).
- The humidity level during harvest is critical to maximising yields (avoiding breakage in protein crops, for example) and especially for improving the storage life of products.