Why humidity is crucial in climate control

By manipulating environmental conditions, and paying equal attention to temperature and humidity, greenhouse growers can improve the quality of their crops and maximise yields. Glenneis Kriel reports.

- Glenneis Kriel

Greenhouse climate control involves optimising the elements to maximise yield at the lowest possible cost, and to do this properly, growers need to understand the effect of vapour pressure deficit (VPD) on plant growth. This is according to Deon van Rooyen, commercial manager at Vegtech Netafim and a speaker at a Netafim South Africa seminar held in Stellenbosch in November.

VPD, explains Van Rooyen, is the difference between the amount of moisture within a plant’s leaves and the air surrounding the plant. It drives various plant processes, such as transpiration, the opening of stomata, and the uptake of carbon dioxide (COâ‚‚) and nutrients.

“By managing respiration rate through VPD, one cannot only optimise plant growth, but ensure that plants stay stress-free and thus healthier. The process further optimises nutrient uptake, resulting in better yields,” he says.

TEMPERATURE PLUS HUMIDITY

Optimal VPD is achieved through the management of the humidity and temperature in greenhouse or tunnel structures.

“When it comes to climate control, growers are normally more focused on temperature than relative humidity, which refers to the amount of water vapour in the air. Humidity, nevertheless, has a much greater impact on plant health and growth than temperature has. Both should therefore be taken into account when using VPD to manipulate plant growth,” says Van Rooyen.

He adds that it means little to know the temperature in an undercover structure without knowing the humidity levels at that temperature.

Unfortunately, there is no ideal VPD setting, as it fluctuates in accordance with relative humidity and temperatures.