How to Ensure You Are Getting the Most Crop Per Drop

By Rebecca Shortt (OMAFRA)

With dry weather across some parts of Ontario this year it’s important to make the most of every drop of irrigation pumped. Making every drop count also increases profits and reduces costs.

Measure how Much Water is Delivered to the Crop Using Buckets or Bowls.

The first big question is: Did every plant get the amount of water I intended?  I have seen drip systems where portions of the field have been receiving NO WATER.  I have seen traveling gun systems where the water application was TWICE AS MUCH as was needed – but some areas only HALF AS MUCH as was needed.  And yet all summer long, pumps were being turned on and farmers were walking away assuming they would get the results of a bountiful harvest.

Measure how much water is being delivered to the crop using buckets (sprinkler/traveling gun) or bowls (drip).  Solutions for overhead irrigation have typically been to increase the overlap between traveling gun pulls and to decrease the depth being applied in each pull (speed up the machine).  This avoids spots with too much water and others with very little or no water.  Similarly, with sprinkler sets, reducing the spacing between sprinkler rows can help improve the coverage.  Solutions for drip irrigation have typically been around increasing the pressure.  Sometimes pumping equipment needs to be replaced in order to increase the pressure (maybe it was never designed to irrigate that field way at the back).  Sometimes filtration stations need to be automated or upgraded – I’ve seen a lot of pressure loss across filtration stations which means you might not have enough pressure to push to the ends of long rows (in the future those long rows may need to be split or shortened).  You’ll never know until you measure.

Schedule Irrigation with Soil Moisture Instruments and/or Evapotranspiration Data

When to start irrigating and how long to run the pumps? Since we don’t have x-ray vision, use soil moisture instruments to “see” how much water you have left in the bank.  Here is an example of what you can see:

The light green line are the soil moisture readings from a probe buried in the root zone, 12 inches below the soil surface (sandy vineyard).  You can see the moisture decreasing each day and then sharply increasing when it rains (grey vertical bars).  You can see how the soil moisture drops quickly at first and then more slowly as the soil dries out and it becomes increasingly difficult for the plant to extract water from the soil.  The PWP (Permanent Wilting Point) for this soil is 6% volumetric water content, that remaining bit of moisture is too tightly bound to the soil particles to be withdrawn by the plant.

There are portable “instant-read” meters; these can be fun and give a sense how the soil moisture is different across the field (mine cost ~$500).  My preferred meter is one with a logger (logging every hour) and at least 2 different depths (mine was ~$300/probe and ~$1,000 for a logger + extra cost for access to cloud based data transfer).  Logging the moisture in the same location over time, you can “see” how the moisture goes up and down and when the plant starts to experience stress.  Did that rainfall soak into the root zone?  Did my irrigation continue down below the root zone?

Here we see the 12 inch deep probe in light green and the 24 inch deep pobe in dark green.  The rainfall (black vertical bars) is seldom getting down to the 24 inch depth – we seldom see the dark green line rising.  There were drip irrigations just before the July 27-28 rainfall and again at the end of the summer.  We can see they raised the soil moisture (light green line) each time.     

Use a Water Meter to Measure and Record Your Water Use

Where can you buy soil moisture instruments?  Your irrigation dealer (http://www.omafra.gov.on.ca/english/crops/resource/irrigation.htm), Hoskin Scientific, Campbell Scientific, Horteau, are others. 

Finally, you can’t manage what you don’t measure.  Purchase and correctly install a water meter.  Record the water meter readings daily or purchase a compatible logger.  Review the daily volumes to understand if the system is operating as you expect.  Too much water – check for leaks.  Too little water – check for plugging or pressure issues.

Generally, in Ontario, I observe irrigation starting too late.  Under irrigation may be the cause of significant yield loss.  In strawberries, studies have shown 50% of ideal water applications has led to 25% yield reduction¹.  In pears, adequate irrigation has reduced corky fruit increasing pack out by 10%².  We know that irrigation pays – why treat it like it doesn’t matter how much or how little we apply?

For more information, see http://www.omafra.gov.on.ca/english/engineer/irrigation.htm

Horticulture VideosMaintaining Drip Irrigation Systems

How to Measure Pressure and Flow in Irrigation Systems

Monitoring Soil Moisture – Part 1

Monitoring Soil Moisture – Part 2

How to Interpret Soil Moisture Results

Monitoring Soil Moisture to Improve Irrigation Decisions http://www.omafra.gov.on.ca/english/engineer/facts/11-037.htm

Jean Caron, Université Laval