Greenhouses
the outset. The Project Manager
is the key person who must be
on the ground from beginning to
end to facilitate interaction of the
irrigation designer and irrigation
contractor with:
XX Agronomy, including:
ZZ Cultural practices
ZZ Nutrition
XX Water source
XX Land-levelling
XX Greenhouse design and
installation including:
ZZ Climate control
ZZ Heating
XX Electrical power supply
XX Infrastructure, including:
ZZ Roads
ZZ Buildings
The Project Manager requires a
clear understanding on who is
responsible for what.The following
highlights some of the key aspects
of a greenhouse irrigation design
to be dealt with early in the project.
Water Supply
A system must be designed to
take water from the water source
to head control / irrigation pump
room, where there is a bulk
storage tank. A flooded suction is
essential in a greenhouse irrigation
system. This supply to the bulk tank
is not necessarily carried out by the
irrigation designer.
This water supply includes:
XX Irrigation water involving the agronomist
XX Service water involving the grower
XX Cooling water - involving the
greenhouse designer
Once the total flow rate is from
these three is decided, it cannot
feasibly be changed later.
Water from the head
control to the greenhouses
Having received the relevant
information from the grower and
the greenhouse designer for the
service water and cooling water
respectively, the systems to take
this water from the head control
to the greenhouses are normally
designed by the irrigation designer.
around a flow rate of 1,2 ℓ/m²/h
(mm/h) comprising:
*CWR = 0,8 ℓ/m²/h +
*L
= 0,4 ℓ/m²/h (33%)
*IFR
= 1,2 ℓ/m²/h
*CWR - Crop water requirement
*L - Leaching
*IFR - Irrigation Flow Rate
The irrigation flow is the probably
largest single contributing factor to
the size and cost of the irrigation
design. It must be decided with
reasonable accuracy as it cannot
feasibly be increased later.
Agronomy –
Nutrition – Dosing unit
A common pitfall is getting the
right fertiliser mixture into the
irrigation water using the dosing
unit. The agronomist knows
what fertiliser is needed and the
irrigation designer knows what a
dosing unit is capable of. Together
they need to come up with the
correct formulation of fertiliser
solution that is capable of being
injected and the correct selection
of the dosing unit that is capable
of injecting the fertiliser recipe.
Agronomy – Nutrition –
Dedicated mainlines
A dosing unit can only inject one
fertiliser recipe at a time. Only
plants that require that recipe can
be irrigated at that time. The effect
of a five minute irrigation pulse is
that fertiliser that is injected into
the irrigation water at the head
control / pump room may not
necessarily reach the plants during
those five minutes.
This means that each block must
have its own mainline downstream
of the point of fertiliser injection.
Irrigation blocks may only share
a mainline if they share the same
fertiliser recipe.
Agronomy – Nutrition –
Areas planted according to
age or cultivar
Plants that require a different
recipe because of age or cultivar
need to be irrigated separately.
This affects the size of the area of
one crop planted at one time and
the area planted according to one
type of crop or cultivar.
The norms for the irrigation
water supply are usually based
14
Figure 4. Elevated irrigation equipment in the head control
SABI | AUGUST/SEPTEMBER 2016
Figure 5. Pipe work installed in covered concrete trenches
Agronomy – crop type and
plant population density
It is important to establish just
which crops will be grown: all
of them, now and in the future.
Different plant population densities
that are multiples of the other can
use the same irrigation equipment.
For example a crop that is planted
at a density of 2 plants / m² and
can share the same irrigation
equipment as one that is planted at
4 plants / m². However cucumbers
for instance at 2,1 plants / m²