Dr Estelle Kempen,
Department of Agronomy, Faculty of Agrisciences, Stellenbosch University
Photos supplied
T
he quality of the water
used to fertigate plants in
soilless systems is vitally
important. Not only should
the presence of potentially harmful
micro-organisms be tested for but,
the chemical composition should
also be evaluated. It is critically important to determine the water
quality as a first step when contemplating growing crops hydroponi-
cally. This will define what crops
can be grown successfully and also
determine the composition of the
nutrient solution to be used.
The total concentration of the ions
in the feeding water, measured as
the electrical conductivity (EC, mS
cm-1) can serve as initial indication
of the quality of the water. High EC
feeding water can only be used to
grow saline-tolerant crops such as
amaranthus, swiss chard, melon
and cherry tomatoes. When the EC
or total salt content of the water
becomes too high, water uptake by
the plants will become limited. As a
general indication figure 1 indicates
the average optimum EC for a
range of crops that can be grown
hydroponically. These values can be
affected by the climate and may
differ between cultivars.
Figure 1: The ideal nutrient solution concentration (EC, mS cm -1) for some hydroponically grown crops.
Figure 1: Tomatoes grown in a soilless systems with a well-balanced nutrient solution. Tomatoes are relatively tolerant to high EC feeding water.
Figure 2: Lettuce plants are sensitive to saline water and
good quality water is essential to produce lettuce in
such a hydroponic system.