DRIP IRRIGATION SCHEDULES

FOR VEGETABLES

By: Kerry Harrison, Extension Engineer

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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

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).

ET x PfDU

Water Use =

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 knownApp. Rate assumes that tape flowrate and wetted area are known

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Irrigated Area and Volume

• With microirrigation, the whole area is not wetted– must adjust water volume

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Volume and Time ExampleAssume 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 “TargetGallons” has gone through flow meter

Step 2b. Calculate operating time for each zone by dividing “Target

Gallons” by pump (zone) flowrate

Application Rate Example

InHr = 96.3 x GPM

Square feet covered

InHr = 96.3 x tape flowrate

Tape length x wetted width

Use 100 feet of row (tape) with high and low flowtape and wetted bed widths of 3', 3.5', 4', and 4.5'.

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Wetting Patterns with Drip Line in Raised-Beds

Clay Soil Loamy Soil Sandy Soil

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 0.062 0.054 0.048

Application Rate for Drip Tape(Inches/hour)

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?)

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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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Time for Break

Maintenance for Drip Systems

PReligious Flushing (both PVC submains and drip lines)PMaintaining adequate flows during flushingPCleaning filters (screen type filters)PHaving adequate pump capacity for filter backflush (media type filters)PPressure gauges to monitor system performance

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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 flushingPCleaning filters (screen type filters)PHaving adequate pump capacity for filter backflush (media type filters)PPressure gauges to monitor system performance

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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 flushingPCleaning 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