by Sonja Heyck-Merlin
Ben and Stacey Waterman own and operate Waterman Orchards in Johnson, VT. The U-pick and wholesale fruit operation includes four acres of highbush blueberries, a four-acre apple orchard and an acre of strawberries. Though not certified organic, the farm is managed organically. In the last of the Spring 2021 Maine Climate and Ag. Network webinar series, Ben Waterman discussed the automated watering system used in their more than 20 varieties of highbush blueberries.
“We operate on sandy soils with very little water hold capacity,” Ben said. “It’s very easy to dump more water on the soil than can be held, resulting in a waste of time and money. At the same time, it’s hard to get enough water.” Blueberries are particularly sensitive to water conditions because of their shallow root systems and lack of root hairs.
“Water management is the difference between big, beautiful, bodacious, bountiful berries and terrible, tasteless, tiny and tainted blueberries,” he said. “When the irrigation is not dialed in, it has an incredible impact on our crop.”
Basic drip irrigation systems typically involve manual valves, which rely on people to control them. “This is how we started out, and it’s a lot of guessing work to open and close the valves to irrigate a particular section of field,” Ben said.
One step toward automation is to put a shut-off timer on your irrigation system. Some timers are controlled by the volume of water that flows through them; others are based on the amount of time the valve is open. A person, however, still has to turn the system on when they think they need water. “The key word here is when you ‘think’ you need water because you never really know,” Ben said.
To eliminate the use of such guesswork in deciding when and how much to water blueberries, Ben and Stacey installed an automated drip irrigation system. Their system uses electric submersible pumps (in their farm ponds) controlled by pressure switches, just like in a household well. The pumps deliver water to mainlines, which supply the drip lines.
A key component of this system is the tensiometer – a one-inch pipe with a porous ceramic tip on one end and on the other, a vacuum-activated switch and gauge. The ceramic tip end of the tensiometer is pushed into the ground, where it measures the tension created by dry conditions. They have eight tensiometers located across their four acres of blueberries because moisture levels vary according to the geography.
Each tensiometer controls an electric valve supplying water to the drip tape. “When the valve opens, the pressure drops in the system and the pressure switch above the pump senses this, and it kicks the pump on. When the valve closes, the pressure builds up in the system, the pressure switch senses that and the pump shuts off,” Ben explained.
Tensiometers can also be wired to a rain sensor gauge. If it’s raining or there is sufficient moisture in the air, the controller will sense that and will not allow the irrigation system to operate and not over-water as a consequence.
There are myriad benefits associated with this system, according to Ben. Because they use fertigation to deliver organic fertilizer to the blueberries, they feel confident that the fertilizer is not leaching below the roots since they are never overwatering. Theoretically, there is less leaching of nitrogen into the environment. They’re saving time because the system is completely automated as well.
“We’re also conserving water,” Ben said. “In the drought of 2016, before we installed this system, we pumped all of our ponds down to complete slime. It was really a drastic situation.” The ponds fared much better during the drought of 2020, and Ben believes that water conservation played a role in keeping adequate water levels in the ponds.
One drawback to the automated irrigation system is that it is not frost-proof. At the end of October, all of the system’s components must be drained. It takes another full day in spring to set up. “It’s hard to avoid this,” Ben said. “If you don’t take the time to drain everything, you get cracks and explosions in the system.” The tensiometers must also be removed in autumn because the liquid inside them can expand and destroy the gauges.
Ben would like to transition to gypsum block moisture meters but hasn’t yet found a way to integrate them into the automated system. Like a tensiometer, this type of moisture meter measures the tension of the soil but does not need to be removed in the winter.
According to Ben, the advantages of their system vastly outweigh the maintenance. “The savings and benefits of installing this system have been tremendous,” he said. “We’ve seen better growth and yield because the soil moisture status is always optimal.”