Some Georgia farmers may see state-mandated irrigation water meters as yet another example of “big-brother”-style government tactics. But the meters can be used to make irrigation systems more efficient, saving both water and money for growers, say state officials.
House Bill 579 — passed by Georgia's General Assembly and signed into law by the governor — requires that water meters be placed on all of the state's permitted irrigation systems.
“House Bill 579 mandates that the Georgia Soil and Water Conservation Commission (GSWCC) place a measuring device on each one of the agricultural water permits in the state,” says David Eigenberg, GSWCC division director.
Farmers who choose to do so can use these state-provided meters as management tools, he says, to help them become more efficient in how they apply water to their crops.
Growers can take the soil-water curves provided for different crops by the University of Georgia and USDA-ARS and incorporate those readings with information from the water meters, says Eigenberg.
“Information from crop water-use curves along with data from the metering device can help you to become more efficient in your crop management schemes,” he says.
How long, asks Eigenberg, will 1 inch of moisture provide water to a growing crop? “We'll assume you have 60-day-old peanuts out there, and if we read the water-use graph, we understand that the crop will use about two tenths inch of water per day. One inch of water will provide moisture to that growing crop — 60-day-old peanuts — for about five days.”
Not all farmers, he says, talk in terms of gallons when they speak about inches of rainfall, or when they speak about water application through a center pivot, he says.
“Many irrigation engineers use a unit of measurement called an acre-inch. If you apply 1 inch of rainfall or 1 inch of irrigation over 1 acre, you're going to apply 27,154 gallons. Farmers understand this unit.
“Whenever you talk to a farmer, you don't ask him how many gallons he applied to his growing crop. We tried to make this management tool match the scheme of your farming operation,” says Eigenberg.
Farmers can use the 27,154 gallons number to do a better job of irrigating and to understand more about their water use, he says. There currently are two or three methods used by farmers to measure the water applied in a field, he adds.
“There's the single rain gauge approach. You set some rain gauges in a field, run your center pivot, and walk over the field. This can give you a pretty good idea of what's applied in certain spots. But the uniformity might vary in that pivot, and we don't know the exact amount of water applied through it.”
Another method, he says, is to use an application chart and a percent timer on your irrigation control panel. “When your pivot is new, this is a very accurate tool. But as time passes and there's wear and tear on the system, the chart can be a little bit off. The best way to know the total volume of water that passes through that system is to place a meter on it.”
The meter itself, says Eigenberg, uses acre-inch increments, or the 27,154-gallon unit. The meter utilizes the same technology as that used in a car, with a speedometer and an odometer.
“With these two tools, you can help identify whether or not you have pumping problems. If you think you're applying 1,000 gallons of water but you're applying only 800 gallons, this tool will tell you that with an instantaneous reading. It'll show you the gallons per minute, and it'll give you an accurate read of the volume that is passed through the pumping unit.”
As an example, says Eigenberg, if you began irrigating with 1400.89 acre-inches on the meter and ended with 1526.11 acre-inches, you know — through simple subtraction — that you applied 125.22 acre-inches through the irrigation system.
To calculate the total gallons of water applied, multiply 125.22 by 27,154.
“We can take it a step further and assume that the water was applied over 140 acres. By simple division, we know we applied about nine tenths inch to that growing crop. We're shooting for about 1 inch every five days, so we're thinking we have enough out there for the five-day time period.”
But, he adds, growers should consider a couple of other factors. “No irrigation system is 100 percent efficient. Some are very close, and with new technology they're getting closer. But there's always potential for loss. There's also the potential for canopy evaporation, drift and even some run-off.”
A good “ballpark” figure for efficiency is 85 percent, says Eigenberg, with the range being between 80 to 92 percent. “But if you multiply that 85 percent by your gross application, you're applying only about three fourths inch to that growing crop. Early in the season, you probably won't see that as a detriment to your crop. But if we have to turn five to seven circles, and we short that crop by one quarter inch each time, we'll probably see some yield reduction, and it'll hit our pocketbooks.”
Installation of the water meters is fairly straight-forward, he says, and they can be installed in either an upright or vertical position.
“The meters will be installed in as farmer-friendly a fashion as possible. It's more complicated than just going out and finding your site, ordering the meter, and putting it in. You'll see commission people on your property, and we appreciate your cooperation.”
There have been many estimates made about agricultural water use in Georgia, but Eigenberg says he doesn't believe some of them are valid.
“Agriculture is a tremendous water user, but not to the point of what the Environmental Protection Division says we are now using. By placing these devices in our fields, we'll get an accurate account of water usage.”
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