By Marshall Hartley
At Florida Southern College, I remember doing an experiment using a large washtub with holes in the bottom. We filled the tub with very dry sand and then poured 1 inch of water over the sand and let it soak in. The water did not travel through the sand evenly. Instead, the water would find one area of the sand to drain through. We repeated the experiment the next day and found that the water drained through the same area of sand.
Dry sand will repel water. This concept applies to citrus growing in sandy soils. Today, citrus groves are not cultivated any more. Growers no longer disk or chop to break up the soil surface so water can get in. So once the area under the tree becomes very dry, water will have a hard time getting into the ground. Trees with a lot of weeds will exacerbate the situation and serve to further dry out the ground under the trees. Growers will then have a difficult time trying to rewet these dried out areas.
The best way to check where your water is going is to dig a few holes and see if the water is penetrating the soil. You might be surprised at what you find.
Cone jets work best with citrus trees less than 2 years old.
FROM CONE JETS TO FAN JETS
I use cone jets for all of my young citrus trees. A cone jet will concentrate the water at the base of the tree. Growers used to put cone jets on PVC pipe for cold protection. I don’t use PVC pipe, so the jets spray about a 12-inch circle around each tree. This type of application of water causes the tree roots to grow deeply downward.
Most growers use fan (fill-in) jets, which cause roots to spread out like a pancake instead of growing downward. After Hurricane Irma, there were a lot of citrus trees blown over with shallow root systems. None of my trees have ever blown over, but some split during Irma and had to be pulled out with a loader. Some of these trees had an impressive 3- to 4-foot taproot.
The irrigation jet is placed too closely to this mature citrus tree. The trunk will block nearly half of the irrigation spray, preventing water from reaching the other side of the tree.
Once my trees reach 1.5 to 2 years old, I switch my cone jets to fill-in jets. Then I move the jets from near the trunks of the trees to midway in between the trees. This is a relatively easy and inexpensive procedure once you realize how the trees will benefit from better irrigation coverage. Moving the jets is simple. No additional hole-punching is needed, as the existing holes and tubing can be used.
BIG BENEFITS
Placing the jets between trees provides full irrigation coverage. Most growers leave their jets next to the trunks of the trees to keep the equipment away from pickers. But when jets are placed so close to trunks of trees older than 2 years, up to 40 percent of the wettable area on the other side of the tree is blocked. This means that 40 percent of the tree’s root system is not getting proper water or fertilizer (in the case of fertigation).
Proper spacing of fan jets between citrus trees allows for more efficient uptake of water and nutrients.
Another advantage of putting the jets in between the trees is easier maintenance. You’ll no longer need to crawl under the trees to repair the equipment when something goes wrong. Additionally, herbicide booms won’t inadvertently knock over the jets once they are moved away from the tree trunks.
The one disadvantage of having jets placed between trees is that pickers may knock some jets over during harvesting. However, the jets are unlikely to break and can be easily stood back up. Since growers normally go through their groves after harvest to clean up, this is the time jets can be checked and propped back up.
Marshall Hartley is a certified crop adviser and citrus grower in Lake Wales, Florida.
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