For those who missed the drip irrigation workshop at the OFVC, here is a summary, giving a step by step that you can use to calculate your approximate run time for your drip system.
Plant water use is driven by the weather. It depends on the temperature, relative humidity, wind speed and solar radiation. These weather parameters can be measured by a weather station and then used to calculate the potential water use called the potential evapotranspiration (ET) in mm. The actual plant water use is moderated by the size of the plant canopy and the “thirstiness” of the crop. This can be described by a number called the crop factor (Kc). Crop factors for berries are listed in the table below. Early in the spring the canopy is very small so the water use is much lower; you can estimate the Kc by considering the % canopy coverage (bare soil, use 0.2 and partial canopy use 0.4 or a percentage of the full Kc). Multiply the ET x Kc to calculate the potential plant water use. Finally, plants will not use as much water if the soil is getting dried out and the plants are stressed (but hopefully that’s not the case in your field!).
ET data can be found at www.farmwest.com and click on the Evapo-transpiration button, where they calculate it from Environment Canada weather station data and also provide a 5 day forecast. Historical average data can be found in the Irrigation Management BMP book at https://bmpbooks.com/publications/irrigation-management/ page 45.
Note that before full canopy/flowering/sizing the crop water demand may be lower but this doesn’t mean lack of water won’t affect yield/quality. Before full water demand, carefully calculate the crop needs and apply the small amounts regularly. For overhead irrigation the water demand should be applied once a week or, when the roots are small, split into 2 applications per week. For drip irrigation water should be applied daily or every other day.
For overhead irrigation, use a rain gauge in the field to make sure you applied what you think you applied.
The calculation of plant water demand should also include a soil factor which slightly reduces the water needs because the soil acts as a water storage reservoir. The calculation should also include an irrigation system efficiency factor which slightly increases the water needs because the irrigation system isn’t perfectly even and in order to get the minimum amount of water to every plant, we need to over irrigate a bit. Since these 2 factors typically balance each other out (in Ontario production systems), we can leave them out and use a “quick” method as shown in the examples below.
Strawberry example in Woodstock for hottest week (Peak ET)
Step 1
ET = 4.9 mm (from table below, using “London”)
Kc = 0.75 (from table below)
Area of each plant (use your actual plant and row spacing)= 1’ x 4’ = 4 ft2
Convert area to metric = 4 ft2 ÷ 10.764 = 0.37 m2
Plant Water Demand = ET (mm) x Kc x Area (m2)
= 4.9 mm x 0.75 x 0.37 m2
= 1.4 Litres/Plant/Day
Step 2
Look on your drip line for the emitter spacing and the emitter flow rate. This example uses a drip line with emitters every 1 ft and flow rate of 1.6 litres per hour.
# Emitters/plant = plant spacing ÷ emitter spacing = 1 ft ÷ 1ft = 1
Flow rate of Emitter = 1.6 lph (litres per hour)
Daily Run Time = Daily Plant Water Demand ÷ (# Emitters/plant x Flow Rate)
= 1.4 Litres/Plant/Day ÷ (1 x 1.6 lph)
= 0.88 hours per Day
Blueberry example in Delhi for hottest week (Peak ET)
Step 1
ET = 5.6 mm (from table below, using “Simcoe”)
Kc = 0.8 (from table below)
Area of each plant (use your actual plant and row spacing)= 5’ x 10’ = 50 ft2
Convert area to metric = 50 ft2 ÷ 10.764 = 4.6 m2
Plant Water Demand = ET (mm) x Kc x Area (m2)
= 5.6 mm x 0.8 x 4.6 m2
= 21 Litres/Plant/Day
Step 2
Look on your drip line for the emitter spacing and the emitter flow rate. This example uses a drip line with emitters every 1.5 ft and flow rate of 2.0 litres per hour.
# Emitters/plant = plant spacing ÷ emitter spacing = 5 ft ÷ 1.5 ft = 3.3
Flow rate of Emitter = 2.0 lph (litres per hour)
Daily Run Time = Daily Plant Water Demand ÷ (# Emitters/plant x Flow Rate)
= 21 Litres/Plant/Day ÷ (3.3 x 2.0 lph)
= 3.2 hours per Day
* Use your own values to calculate the water needs of your berry crop.
** Use the ET data from www.farmwest.com in your calculations during the growing season. You can use a ratio so you don’t need to go through the whole calculation again. See example for early August 2022 below
Blueberry example in Delhi for Aug 5-11, 2022
Peak ET = 5.6 mm (from example above)
Peak run time = 3.2 hours (from example above)
Aug 5-11 ET = 3.9 mm (from www.farmwest.com)
Aug 5-11 Run time = Peak run time/Peak ET x Aug 5-11 ET
= 3.2 hours/5.6 mm x 3.9 mm
= 2.2 hours
This is how long to run the drip lines for that example field and drip system when the weather was cooler in early August of 2022.
Peak Evapotranspiration (ET) for Trickle Irrigation Design
Location | Peak ET mm/day |
Windsor | 5.4 |
Ridgetown | 5.2 |
London | 4.9 |
Simcoe | 5.6 |
Vineland | 5.3 |
Toronto | 4.9 |
Mt. Forest | 5.3 |
Trenton | 5.1 |
Ottawa | 5.0 |
North Bay | 4.2 |
Thunder Bay | 5.1 |
From the Ontario Irrigation Management BMP book https://bmpbooks.com/publications/irrigation-management/
Crop Coefficient (Kc)
Plant | Crop Coefficient | Approximate plant spacing |
Blueberries | 0.8 | 5’ x 10’ |
Raspberries | 0.7 | 2.5’ x 10’ |
Strawberries | 0.75 | 1’ x 4’ |
From the BC Trickle Irrigation Manual by Ted Vander Gulik, BC Ministry of Agriculture and Food and the Irrigation Industry Association of British Columbia, 1999
https://www.irrigationbc.com/product/bc-trickle-irrigation-manual
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