Grape Irrigation – Both art and science

by Rebecca Shortt, Engineer, Water Quantity, OMAFRA

It’s a delicate dance to get just the right amount of water on grape vines at this time of year.  Water is crucial for cell division and the rapid berry growth occurring.  However, too much water can cause too much vegetative growth.

Dr. Andy Reynolds of Brock University has shown that irrigation between 0 and 100% ETc is best for balancing grape production and vine vigour.  Sauvignon Blanc in 2006-2008 responded best to a program of 25%ETc resulting in improved grape composition and wine aroma typicity.  Cabernet Sauvignon in 2006-2008 with deficit irrigation improved grape composition.  Earlier work on Chardonnay in 2001-2004 showed that irrigation increased yield by 18-19% with a similar to higher Brix, higher soluble solids and greater intensities of apple, citrus and floral aromas and flavours as well as lower levels of earthy aroma and flavour.

So what is deficit irrigation?  Basically it means giving the vines small drinks of water on a regular basis so that the vine experiences some stress but not enough to cause quality or yield impacts.

How to calculate the length of time to run my drip system each day?

Use www.vineandtreefruitinnovations.com/ (free but you must register) to see the daily evapotranspiration (ET) measurements for wine grape areas.  Use the ET multiplied by a crop factor (Kc) of 0.75 to get the maximum depth of water the vines can use.  Multiply again by 0.25 to 0.75 to create some stress in the plants.

Drip irrigation example in NOTL (parkway)

ET June 17-23 = 27.9mm

ET daily average = 4mm

Kc = 0.75

Maximum vine water use per day ETc = ET x Kc = 4 mm x 0.75 = 3 mm

Deficit irrigation (I’m choosing to only apply moderate stress of 0.50 because this is a critical time for berry development)

Deficit Irrigation ETd = ETc x deficit% = 3mm x 0.50 = 1.5mm

How much water do I need to apply?

Your vine area x ETd x units conversion factor (0.0245)

= 9ft x 4ft x 1.5mm/day x 0.0245

= 1.3 U.S.gal

Gallons/Plant/Day = G/P/D = 1.3 gal

How long do I need to run my drip system?

Run Time = Gallons/Plant/Day ÷ (Number of emitters/plant x Emitter Flow Rate)

If my vines are spaced every 4 ft and the drippers are every 24 inches, then I have 2 emitters per plant.

In this example we’ll use 0.42 gph for the emitter flow rate

Run Time = Gallons/Plant/Day ÷ (Number of emitters/plant x Emitter Flow Rate)

= 1.3 gal ÷ (2 x 0.42gph)

= 1.5hrs

If the weather is similar to last week you can run this example system for 1.5hrs every day or 3hrs every other day to provide some water and 50% stress to the vines.