Lettuce in a growing system where
the nutrient rich water is continually
being re-circulated.
course to a large degree be determined by the quality of the water
used to make up the nutrient solutions. Water containing large
amounts of ions not readily taken
up by plants, Na+ and Cl- usually,
will need to be flushed before a critical level is reached. One way of improving the water quality and therefore the time that you will be able
to re-use the water is by mixing it
with rainwater. In Europe it is standard practise to collect all the rainwater from the greenhouse roofs on
average 500 m3/ha can be collected
in the Netherlands. In South Africa
very few producers still do that and
in certain areas, especially the winter rainfall areas it is not that practical.
Producing crops in a soilless system
in a greenhouse therefore enables
different levels of increasing the
water and nutrient use efficiency
depending on the technology and
management practises employed.
A simple method of collecting
and storing drained nutrient rich
water from grow bags before
re-using it to fertigated plants.
A slow sand filter can be used
to remove pathogens from the
water before re-using it in your
hydroponic system.
A small wetland system outside
the greenhouse is used to remove unwanted elements from
the water when the water cannot be re-circulated in the hydroponic system anymore.
Figure 1. Amount of irrigation water required to produce 1kg of tomatoes