hOW TO SUCCESSFULLY CHOOSE GROWING...
Figure 3
diseases present in high
humidity conditions.
Container size and shape
It was mentioned earlier that the size and shape of the
containers in which the medium is placed determine the
amount of water that the media hold. Take a look at the
containers in figure three: All containers are of the same volume
and are filled with the same medium. The blue area represents
water. Since it is the same medium, the water reaches the same
height in each of the containers. Moreover, according to the
water retention curve of this medium, the same water content
in per cent is measured at this height.
However, due to the different shapes, the actual amount of
water is different in each container. This results in a different
water/air ratio in each container and in different irrigation
management. Irrigation frequency and amount of water applied
with each watering are determined by the available water
content of the medium and by the container shape and size. For
example, one irrigation cycle a day is not enough if the daily
water consumption of the plant is higher than the amount of
available water in the medium.
Hydraulic conductivity
88
Maximum Yield USA | September 2012
As the name suggests, hydraulic conductivity is the rate at
which a medium transmits water. Hydraulic conductivity of
media is not routinely measured in lab tests. Nevertheless, it is
extremely important to understand its significance. Hydraulic
conductivity is, in fact, the limiting factor of water uptake by
plants in container media (rather than the water quantity in
the medium).
When transpiration rate exceeds the hydraulic conductivity
of the medium, the plant cannot efficiently use the water
contained in the medium and could wilt. In materials used
for container media, the hydraulic conductivity decreases
exponentially as the medium dries. This is because continuity of
water is disrupted after the larger pores empty. MY