Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
methods namely, (1) fertilizer tank (the by-pass system), (2) the venturi pump and (3) the injection
pump (piston or destron pump). Non-corrosive material should be used for the fertilizer containers
and for the injection equipment.
8. Design of Irrigation System Considering Chemigation
After determining the type of irrigation delivery system, it is important to design the system
so that it delivers fertigated water as uniformly as possible. Distribution uniformity (D.U.) should be
in the 80% or higher range. This means 20% or less of the applied water will be wasted. If lower
D.U.s are used, some plants will not receive adequate fertilization while others will be overfertilized.
This will occur with any D.U. below 100%, so the higher the D.U. the more effective the
fertigation. Second, the system must be able to meet the scheduling demands dictated by local
regulations, proper horticultural practices, and the fertigation system itself. It is generally desirable
to have all fertigated water flushed from the system at the end of the irrigation cycle. So the
fertigation system should be designed to deliver fertilizer fast enough to allow the system to
operate, after fertigation, for a long enough period of time to flush all lines. This should occur
without having longer-than-required run times for providing the necessary water to the landscape.
While this is often possible in smaller systems, larger systems often retain some fertigated water
after the watering cycle. At minimum, the system must be designed to allow the required amount
of fertilizer to be applied during normal watering run times. The following steps can serve as a
general guide for making the above determinations.
First, calculate the LPH for each zone (to determine precipitation rates) and the required
run time to provide optimum water for the plant material. Second, determine the volume of water in
the piping from injection point to the furthest sprinkler, in each zone. Now compare these two
figures for each zone and determine which zone has the largest required run time to receive
fertigated water. This will be the "critical zone" for fertigation design purposes. Using the
quarter/half/quarter rule (system runs for one-fourth of its total programmed run time before
fertilizer injection begins, injection occurs for half the run time, injection ceases for the final onefourth
of the run time) determine the allowable fertigation run time within the zone's "total run time."
Finally, determine what concentration the fertilizer will need to be at to fit inside this "fertigation
window."
This is the point where compromises may have to be made between complete flushing of
piping, realistic concentrations and injection rates. The only component that should not be
compromised is the overall run time for each zone. The correct amount of water should always be
delivered to the plant material. Excess water should not be applied just to allow fertigation. This
would be counter-productive. The fertigators have more flexibility on using liquid fertilizers as
compared with water soluble granular fertilizers.
9. Conclusions
The precision farming and hi-tech agriculture for the improved input use efficiency, more
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