Evapotranspiration Control in Hydroponics!
© a.k.a. MBR
In conventional gardening and farming outdoors and in greenhouses, it can be beneficial to control and reduce evapotranspiration rates to reduce water usage where it is scarce. This can also be useful in hydroponics systems where water conservation is desired.
There are many means available to reduce water loss indoors and out such as using plastic mulches, anti-transpirant sprays such as waxes, misting the plants with water, and wind breaks but there must be a balance achieved between limiting water requirements and maintaining crop productivity and yield.
While a layer of plastic liner over the substrate will definitely reduce evaporative losses, it could also result in damage due to an oxygen deficiency occurring in the root zone which would reduce crop yield potential (see our previous article on oxygen availability). For this reason, if plastic mulches are to be used (preferably opaque white ones to reduce algae growth and to reflect light back up towards the plants leaves), they should be cut away from the area directly surrounding the plants' stem and roots to allow for air exchange and oxygen replenishment. We recommend using a permeable cloth such as landscape fabric which will reduce evaporation significantly, while allowing for the roots to "breathe".
Cuttings and transplants can gain from the use of clear plastic or glass humidity domes and/or anti-tranpirant sprays that help to prevent shock inset due to water loss. These allow for faster acclimatisation to their new growing environment, but care should be taken to avoid stifling the plants. Another method that has been proven to be effective is to prune some of the larger leaves off of the cutting or transplant.
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