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soil moisture probe being installed in soil beneath citrus tree

Soil Moisture Probes for Citrus

Can you tell when your trees need water? Most growers can see the angle of the leaves and know immediately that their plants need water. If the soil is already moist, then they know they have a root problem. Letting your trees get to the point that they tell you they need water means that they are stressed, and stressed plants don’t yield as well as unstressed trees. Especially if your citrus has HLB (Citrus Greening) where any stress increases the chances that tree will not thrive.

Ways to Measure Water Use

How do you know when your trees have had enough water and it is time to turn the irrigation off? The old rule of thumb was to get the water all the way down to the deepest roots – four feet down – and irrigate for hours to get there. HLB affected trees don’t have roots four feet down, even on the ridge. Watering that much is a waste of water, fertilizer, and probably plant health. How much water you need to apply can be measured various ways. You may just guess based on your experience and historic water use (this has changed with HLB), use schedules like those found at Management of Microsprinkler Systems for Florida Citrus, use the Florida Automated Weather Network website (FAWN), or use your own weather station to find out the evapotranspiration from your site and calculate how much water is needed to replace what your trees used. What if you could know how much water there was down in the root zone and know exactly what was needed? That is what a soil moisture sensor can do for you. So why aren’t we using them?

The old tensiometers or irrometers I used in the 1980s measured soil moisture with a column of water, a porous tip, and a pressure gauge to measure the pressure required to pull water from the column. When I used these in the past I was frustrated enough to call them errometers because you could not always trust what they said – if the water column broke, if the gauge wasn’t quite right – too many things could go wrong and did. Then new technology brought new measurement techniques, a much higher price tag, and much more technical displays, but a really reliable measurement.

Barriers to Adoption

What is keeping growers from using these new soil moisture sensors? Many feel that you have to have a PhD to be able to tell whether your plants need water or not using the computer graphical interface. It really is just a new thing to learn and not that difficult once you get the hang of it. And if you don’t want to have to learn a new thing, there are companies that provide that service. What about the cost? These new sensors can cost $1,800- $2,200 plus a service contract between $200-$700/year depending on the vendor, and that is beyond what most growers want to pay, especially if you need several probes. However, there are cost share programs from multiple agencies that can bring that price down to a much better range, and there are new soil probes coming out all the time that are less expensive as the technology becomes cheaper.

Cost Share Programs

What are these cost share programs? First, the Florida Department of Agriculture and Consumer Services (FDACS) has cost share that will reimburse producers for the purchase of soil moisture probes and the first year of maintenance at a 75% rate. The St. Johns River Water Management District (SJRWMD) Districtwide Agricultural Cost Share Program collects applications up to two times per year and ranks projects on criteria including benefit to the resource, cost effectiveness and proximity to areas of resource concern.  Selected projects are funded up to 75% with a cap of $250,000. Soil moisture probes are eligible for funding and would include the probes, installation, training and the first year’s subscription fee. And if that is not enough, the National Resource Conservation Service (NRCS), within the Environmental Quality Incentives Program, has financial assistance for irrigation water management which includes soil moisture sensors up to $1,895, depending on the type. You can combine the various cost share programs to get a full 75% coverage, but you still have to pay 25% of the cost for FDACS and SJRWMD. The NRCS cost share does not base their payment on any percentage, it is based solely on a table of allowed expense. That really is not that much considering what you can save in water, fertilizer, and tree health. What is keeping you from adopting this technology?

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