The need to manage water efficiently is a major concern in the use
of scarce resources. Responsible action is increasingly supported
by legislation and the higher price of using water. Clearly the major
factors that determine the level of water use are related to the choice
of plant species to be grown and the reasons for growing. The
selection of drought-tolerant rather than water intensive plantings
. Some growing systems are inherently less water
intensive, but in most of them there are many ways in which water use
can be reduced if certain principles are kept in mind and acted upon
- Whenever possible, the use of artificial water should be avoided.
- Use recycled water. The recycling of water and the capture of
rainwater are important considerations in the choice of water source.
- Minimize evaporation of water. This is best achieved by not
spraying water into the air and by minimizing the time when the soil
surface is moist. When water does have to be applied overhead, this
should be undertaken in cool periods.
- Increase the water reservoir of the soil. The application of water
can be reduced by increasing the growing medium’s water holding
capacity; most soils can be improved by the addition of suitable
- Encourage plant root systems. Plants should be encouraged to
establish as quickly as possible but, after the initial watering-in,
infrequent applications will encourage the plant to put down deep roots
by searching for water. Most importantly, soil pans should be eliminated
and good soil structure maintained to increase the rooting depth.
- Minimize water lost through drainage. Where application is
partially controlled, the correct relationship between water applied
and water holding (see water-holding capacity) helps to prevent
leaching, which leads to nutrient loss (see nitrogen), as well as
wasting water. Thus returning an outdoor soil to less than field
capacity helps avoid losses by drainage or run-off in the event of
Water is lost more rapidly from a moist than from a dry soil surface.
After just 10 mm of water has been lost from the surface, the rate of
evaporation falls significantly. Infrequent application thus helps, but
even more effective is the delivery of water to specific spots next to
plants (see trickle lines) or from below through pipes to the rooting
zone. Avoid bringing moist soil to the surface. If hoeing is undertaken
it should be confined to the very top layers; this also reduces the risk of
root damage. Losses from the surface can be reduced considerably by
plant cover and almost eliminated by the use of mulches. Loss of water
from the plants themselves is reduced when they are grouped together
rather than spaced out.
Unless maximum growth rates are the main consideration, reduced
saves water, money and staff time without detriment to most
plantings. In production horticulture, the introduction of sophisticated
moisture-sensing equipment and computer controls has enabled water to
be delivered more precisely when and where it is needed. This has led to
considerable reduction in water use.
Nutrient loss and run-off from overhead watering
used in container
nursery stock production can be minimized by matching application
to rainfall, growing medium, container size, plant species, stage of
growth and time of year. Nozzles should be maintained to ensure even
water application. Loss from sub-irrigated capillary sand beds tends
to be lower. Recirculation (closed) systems should be considered in
new developments. The quantity of water required for flooding
protected culture (e.g. to remove excess nutrients when a crop sensitive
to high salt levels, such as lettuce, is to be grown after a tolerant one,
such as tomatoes), can be reduced by discontinuing the liquid feeding of
the previous crop as soon as possible.
In non-recirculating (open) hydroponics systems
excessive water waste
should be avoided by using fl ow meters to measure the quantity of
run-off and comparing it with standard figures for the growing system
used. A run-off of over 30 per cent is usually considered to be excessive
and the amount and frequency of nutrient applications delivered by the
nozzles or drippers should be reviewed. Closed systems (see NFT)
recirculate the nutrient solution, but this is not always practical. Where
they are used, the system must not be emptied illegally into watercourses
or soakaways. It is recommended that the volume in the system be run
down before discharge and the waste nutrient solution be sprayed on
to crops during the growing season. Permission to empty into public
sewers might be granted, but it is usually subject to a charge depending
on volume and contamination level.