Irrigation’s Changing Face

02/01/2010 02:00:00 AM
Steve Heisler, contributing writer

Tomato and pepper growers face one major irrigation issue across Florida—how to most efficiently deliver water and nutrients to plants’ roots in widely diverse soil types.

From the deep soils of north Florida to the sandy ridge in the central part of the state and the challenging uncoated sands of Immokalee, growers are embracing new technology and using soil moisture sensors to meet that need.

“The challenge becomes if you go out and over-irrigate, you tend to leach the nutrients from the growing beds below the surface,” says Bob Hochmuth, a Suwannee-based multi-county Extension agent. “Sensors are important helping us determine when the farmer should turn on the irrigation and how long it should be run.”

Hochmuth, with the Institute for Food and Agricultural Science, has watched as sensors have evolved during the past few decades. When drip irrigation was fine tuned 15 years ago, tensiometers were popular.

They’ve given way to granular matrix sensors, such as The Watermark, which measure soil water tension through electrical resistance readings.

More recently, many growers have chosen the time domain reflectrometry, or TDR, probe. A portable TDR is available for about $600. It uses two prongs buried in the soil to measure moisture near the surface, in the root zone and beneath it. The prongs are wired to a controller that can start or end an irrigation set.

“That one is going to give the best information about what’s happening in the entire soil profile,” Hochmuth says of a TDR probe. “The technology in the soil sensor area is greatly improved in the last five years. The utilization at the farmer’s level has made that quantum leap.”

Soil variability plays a role

Growers in Immokalee face this issue regularly. Although some use the FAWN weather network as a predictive model with evapo-transmitters, most of those who farm the area’s collective 5,000-plus acres of peppers and 22,000 acres of tomatoes opt for the TDR.

South Florida’s sandy soil particles are uncoated and don’t bind well with phosphorus. As a result, phosphorus may easily leach into environmentally sensitive areas if too much water is applied, says Gene McAvoy, a regional vegetable agent and Hendry County Extension director in Immokalee.

“Our soil has gone from drought to flood in 10 to 14 days; there’s no buffering capacity,” he says. “We’re constantly moving water, taking it off the land or putting it back on.”

McAvoy’s research focus is to develop nutrient profiles so over-watering and over-fertilization don’t occur. Too much nitrogen can open the door for diseases, such as bacterial spot and viruses spread by whitefly.

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