How Long Do I Run My Drip Lines?

By Rebecca Shortt, Water Quantity Engineer, OMAFRA

This blog post will show the 2 steps to roughly calculate how long to run a drip system.

First calculate the plant water demand.  This was shown in my post from last week.

Plant Water Demand (U.S. gal)

= ET (mm) x Kc x Area occupied by plant (ft2) x conversion factor 0.0245

  • ET from (free but you must register) or
  • Kc (Crop Factors) from the tables below and/or consider extent of canopy
  • Area occupied by plant is the row spacing x the plant spacing
    • If there is significant space without crop canopy between rows (e.g. apple trees which have been hedged) then this area could be reduced. Keep in mind that the Kc (crop coefficient) may be partially accounting for this already (e.g. strawberries have Kc of 0.75 partly because we assume bare straw between rows).  Also keep in mind that living cover crops between rows will be competing with the crop for water.

Second, divide the Gallons/Plant/Day by the number of emitters per plant x emitter flow rate.

Daily Run Time = Daily Plant Water Demand ÷ (# Emitters/plant x Flow Rate)

Hops example in Prince Edward County

Step 1
ET July 1-7 = 24mm/7days = 3.4 mm
Kc = 1.05
Area = 0.9m x 3.7m = 3.3 m2          (3’ x 12’ = 36 ft2)

Plant Water Demand = ET (mm) x Kc x Area (m2)

= 3.4 mm x 1.05 x 3.3 m2
= 11.8 Litres/Plant/Day

Step 2
# Emitters/plant = plant spacing ÷ emitter spacing = 0.9 m ÷ 0.45 m = 2
Flow rate of Emitter = 1.6 lph (litres per hour)

Daily Run Time = Daily Plant Water Demand ÷ (# Emitters/plant x Flow Rate)
= 11.8 Litres/Plant/Day ÷ (2 x 1.6 lph)
= 3.7 hours per Day

Note: in Norfolk county where the ET has been 4.4mm per day the run time would be a ratio 3.7hrs x (4.4mm/3.4mm) = 4.8 hours per Day

Ginseng (3yr garden) with 2 drip lines per bed, example in Simcoe
Step 1

ET July 1-7 = 31mm/7days = 4.4mm
Kc = 0.8
Area = emitter spacing x bed spacing = 0.3m x 0.9m = 0.54 m2           (= 1’ x 6’ = 6 ft)

Plant Water Demand = ET (mm) x Kc x Area (m2)

= 4.4 mm x 0.8 x 0.54 m2
= 1.9 Litres/Area/Day

Step 2

# Emitters/Area = 2 (because there are 2 drip lines, there are 2 drippers for every 0.3m)
Flow rate of Emitter = 1.6 lph (litres per hour)
Daily Run Time = Daily Plant Water Demand ÷ (# Emitters/Area x Flow Rate)

= 1.9 Litres/Area/Day ÷ (2 x 1.6 lph)
= 0.6 hours per Day

Estimated crop factors for ginseng (Kc)

1 year garden 0.3
2 year garden 0.7
3 year or 4year garden 0.8

Kc Crop Factors for other specialty crops see previous post

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
This entry was posted in All Specialty Crops, Culinary, Ginseng, Ginseng Production, Goji, Haskap, Herbs, Hops, Hops Production, Lavender, Medicinal, Other Herbs, Other Specialty Fruit and Nuts, Other Specialty Vegetables, Sea Buckthorn, Specialty Fruit and Nuts, Specialty Vegetable Production, Specialty Vegetables, Tree Nuts and tagged , , , , , , . Bookmark the permalink.

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