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Managing Irrigation During Dormancy

Hortau in Dormant Almonds

The East Coast and much of the Midwest and Plains states are grappling with the aftermath of bomb cyclones and the polar vortex. But on the opposite end of the country, California is entering the new year following one of the driest Decembers in a century, leaving the Golden State’s growers questioning when it’s time to fire up the irrigation.

Whether the weather in California turns around and more rain shows up is really a craps shoot, and growers shouldn’t wait for the rain to keep their soils properly hydrated. It’s important to make it a priority to provide all water to the soil through irrigation, and any extra that comes in the form of precipitation should be considered pennies from heaven.

For citrus and select cool-weather row crops that are in full production through the winter months, the strategy is pretty straight forward: irrigate to the needs of the crop.

But for dormant crops like stone fruit, nuts, and grapes that aren’t pulling nearly as much water as the spring and summer months, irrigation management can be a guessing game if you don’t know what’s happening below the surface. If that’s the case, you could be putting your crops at risk of damage.

“Winter dormancy is a time where plants reduce their metabolic activity and make some minor physiological changes to cope with freezing weather that would be damaging if it weren’t for dormancy,” says Ben Smith, Hortau director of grower support and irrigation scheduling. “Although trees, vines and bushes are dormant, they are still living, just at a slower rate.”

Smith likens the dormancy of deciduous crops to a hibernating bear.

“Bears sleep for several months in the winter, relying on what they were able to stockpile in their bodies,” he says. “However, they are still living. If someone were to shoot a sleeping bear while sleeping it would still die. Similarly, dormant plants are vulnerable to death, even in their hardened, dormant state.”

While peppering your trees with buckshot may not kill them, the overly dry soils that can occur during the winter have the potential to put them at risk for damage or worse.

Soils can dry out due to a number of reasons including poor post-harvest irrigation management, lack of precipitation or cold temperatures, or a combination of all of those factors.

Frost Near a Young Almond OrchardCold air, specifically, has a tendency to dry out the soil, as it does not have the capacity to hold as much moisture as warm air. As temperatures drop there is an increase in the gradient that promotes the evaporation of water from the soil, in turn drying it out.

We can’t control the temperature, but we certainly can control irrigation.

For deciduous crop growers, it’s important to produce conditions that support a “healthy” dormancy for trees, vines and bushes in order to help establish more robust crops heading into bloom and leaf-out. Effective irrigation management while the crops are sleeping is one of the ways to ensure this.

If you use Hortau’s precision irrigation management system, managing crop stress during dormancy is still as simple as staying between the lines. In fact, some might argue that it’s easier in the winter time because you don’t have to battle with the plants pulling water the way they would during the warmer months.

Keeping soil tension between the boundaries of the blue band (tension thresholds) on the graphs assures growers that soil moisture is ideal for dormant plants. In addition to keeping tension steady, growers irrigating to keep their dormant trees, vines and plants in the comfort zone will also benefit from keeping the soil profile full, as well as leach salts from the profile, and protect roots from frost damage.

PROTECTING ROOTS, FILLING THE PROFILE AND BEYOND

If you read our blog post on rehydrating soils after a deep loss in soil moisture, you would know that it’s a long and tedious process to restore soil moisture, regardless of the time of year. If your post-harvest irrigation was lackluster, now is a good time to consider starting that refill process as to not get caught off guard by a potential early break in dormancy.

“Dormancy is an ideal time to get everything topped off and ready to go for next year, but don’t expect that one irrigation will do all the work,” Smith says. “If rainfall is very low, a field may require multiple irrigations throughout the winter to keep conditions in a suitable range.”

Touching on the opposite end of that spectrum, it is to crucial not over-assume that heavy rain events will infiltrate to your entire soil profile. Just because it’s wet on the surface, doesn’t necessarily guarantee it’s going deep. In fact, Smith says that a typical storm in California will really only fill up the first 12- to 18-inches, leaving the lower —and most productive — part of the profile dry (you can read more about managing irrigation during wet years here).

Another benefit to irrigation during dormancy is the opportunity to flush salts beyond the root zone to help start the year with a clean slate before more nutrition is added prior to bloom. While it’s discouraged to allow leaching to occur during the season (unless you enjoy throwing away money on nutrients that your crop doesn’t use), the dormant months offer a good opportunity to implement a winter leaching plan that prepares the soil to receive new applications of nutrients come spring.

“Winter is the one time of the year that leaching should be promoted,” Smith says. “Take advantage of the crops not using water to fill the profile and then to cause several, at least three, leaching events to move salts out of the root zone. There is nothing like a fresh start at the beginning of the year.”

Perhaps the most important reason to irrigate during dormancy is to protect root structures from drying out and dying as a result of cold weather. Dormant trees with deeper root systems are better at protecting themselves from dry conditions, but if the soil gets too dry, growers risk desiccating vital feeder roots that the trees will have to expend energy to regrow in the spring— taking energy away from pollination and foliage development.

Grape Vines Heading Into DormancyNon-tree crops, such as grapes, blueberries or bramble fruits, have shallow, frost-sensitive roots and are extremely susceptible to dry soils that result from cold weather. Keeping the soils moist will help buffer the roots from potential cold damage because water is excellent at storing heat and releasing it when it gets cold.

“A moist soil will soak up heat during the day and then buffer cold temperatures at night by releasing the stored heat,” Smith says. “Dry soils cannot hold very much heat, which can lead to frost damaged roots under the soil.”

With Hortau’s precision irrigation management system growers are able to see what’s happening below the surface so they can make informed irrigation decisions in any season.

To learn more about irrigation management with Hortau, set up a consultation with a representative in your area.