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DRIP IRRIGATION SCHEDULES
FOR VEGETABLES
By: Kerry Harrison, Extension Engineer
Irrigation Scheduling
• If the crop is using 0.25 inch of water per
day, when do we need to irrigate
– if the soil was at field capacity, and the crop
pulled out 0.25 inch per day
– then we need to irrigate every four days and put
down 1.2 inches of water
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SCHEDULE: Must know how much is needed
(I. E. 0.10 inches)
Amount: Should be expressed in volume or
depth - not time (i.e. 0.1 inches not 30 minutes).
Water Use =
ET x Pf
DU
Where: ET = evapotraspiration
Pf = plant factor
DU = low quarter uniformity
3 Methods Used to Calculate “how much”
•By Volume
•By Time
•By Application Rate
Assumptions: Both volume & time assume the acres per zone and flow are known
App. Rate assumes that tape flowrate and wetted area are known
Irrigated Area and Volume
• With microirrigation, the whole area is not
wetted
– must adjust water volume
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Volume and Time Example
Assume you want to apply 0.1 inches
Step 1. 0.1 in. X 27,000 gallons/ac-in X Acres/zone = “Target Gallons”
Step 2a. Set programmable timeclock to stop operating after “Target
Gallons” has gone through flow meter
Step 2b. Calculate operating time for each zone by dividing “Target
Gallons” by pump (zone) flowrate
Application Rate Example
In = 96.3 x GPM
Hr
Square feet covered
In = 96.3 x tape flowrate
Hr
Tape length x wetted width
Use 100 feet of row (tape) with high and low flow
tape and wetted bed widths of 3', 3.5', 4', and 4.5'.
Wetting Patterns with Drip Line
in Raised-Beds
Clay Soil
Loamy Soil
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Sandy Soil
Application Rate for Drip Tape
(Inches/hour)
Wetted width
3'
3.5'
4'
4.5'
HF (0.45 gpm per 100') 0.145 0.124
0.109
0.096
LF (0.225 gpm per 100') 0.072
0.054
0.048
0.062
Notes: Tape flowrate can vary depending on pressure.
Application width depends on soil type
Wetting Patterns: Are influenced by “pulsing”
Frequency: Should include scheduling
management (i.e. 0.25"/day is the same as
1.75"/week but how was it applied?)
Irrigation Frequency
• In order to maximize yield, you must
– understand the water requirements of the crop
– understand the relationship between
• the plant
• the soil
• and the water
– understand the design of the irrigation system
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Timefor Break
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Maintenance for Drip Systems
PReligious Flushing (both PVC submains and drip lines)
PMaintaining adequate flows during flushing
PCleaning filters (screen type filters)
PHaving adequate pump capacity for filter backflush (media
type filters)
PPressure gauges to monitor system performance
600-foot Length on Zero Percent Slope
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Maintenance for Drip Systems
PReligious Flushing (both PVC submains and drip lines)
PMaintaining adequate flows during flushing
PCleaning filters (screen type filters)
PHaving adequate pump capacity for filter backflush (media
type filters)
PPressure gauges to monitor system performance
Distribution and Filtration
• Pressure requirements and pumps are
unique to each site
– must know elevations, and acreage
– must know pipe sizes
– must know flowrates
• Need to have a qualified designer or
engineer provide assistance with pump
selection
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Water Filtration
• Three basic types of filters
– media filters (sand filters)
– disk filters
– screen filters
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Maintenance for Drip Systems
PReligious Flushing (both PVC submains and drip lines)
PMaintaining adequate flows during flushing
PCleaning filters (screen type filters)
PHaving adequate pump capacity for filter backflush (media
type filters)
PPressure gauges to monitor system performance
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Wrap-up
• Filtration is the key to long-term success
with microirrigation
• Understanding how the whole system works
is the key to being a successful irrigator
– system includes the plants, the soil, and the
water
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Final Words
• Use many pressure gauges.
– these are your indicators as to the health of the
irrigation system
– make sure there is enough pressure without
there being too much pressure
• Flush the dripline
– open the end while the system is running and
flush the solids out
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