Push a button on a data logger or a handheld meter, read the number and line it up with your soil type in a table of soil-moisture levels. That's it. You have the answer to whether you need to irrigate.
It's that simple.
That simplicity has a number of south-central and central Nebraska irrigators enthused about putting precision in their irrigation scheduling. It's generally allowing them to cut out one or more irrigations a season. And, at $1,000 or more in energy cost per irrigation on a typical quarter-section center-pivot installation, that's not to be shrugged off, say irrigators Dennis Valentine, Hastings; Walt Traudt, Clay Center; Jerry Stahr, York; and Gerry George, Waco. Maybe even more important in many areas of the country is the savings in water — an increasingly precious resource.
While this scheduling system can be used with gravity irrigation as well as pivot-irrigated fields, pivots allow more control over timing and application amounts to fit tighter scheduling.
Equipment costing $300-500 can let an irrigator do that on several irrigated fields.
Valentine, Traudt, Stahr, and George are just four of more than 300 south-central and central Nebraska irrigators trying the newest soil-moisture-sensor technology as part of the Nebraska Agricultural Water Management Demonstration Network (NAWMDN). The network began with just 18 irrigators four years ago, according to Suat Irmak, soil and water resources engineer at the University of Nebraska-Lincoln. That's how fast this technology is catching on. Irmak has developed a system that simplifies using this equipment.
TRAUDT USED TO manually probe to 1-, 2- and 3-ft. depths to see if soil pulled from the probe was becoming too dry to ribbon in his hand, an indication that he should irrigate; not exceptionally precise and not an easy chore in a hot, humid cornfield.
Now, he says, “We can pull up and jump out of the pickup and — boom, boom — I've got the reading.
“For us, it took all of the guesswork out of irrigating,” Valentine adds. He irrigates land near Fairfield, NE, with his brother Rod. They've used the sensors for irrigation scheduling the past two years under three quarter-section pivots of corn and soybeans on a silty clay loam soil.
“What sold me was saving two irrigations on corn,” Valentine says. “On soybeans, I know we saved an irrigation.”
Stahr, who irrigates corn and soybeans on silt loam soil — much of it under center pivots — says moisture monitoring gives you not only “a good grip on when the crop needs to be irrigated, but helps you hone in on the amount you want to put on. In all, you're saving at least 20% (in pumping).”
George, who used gypsum blocks “years ago,” says he is “more comfortable with the sensors,” which he reads with a handheld meter. He's participated in the water management network for several years and estimates that the sensors have helped him cut back irrigation by one application every season.
The first year, Valentine says, “I questioned the sensor readings a little bit.” Now he and his brother confidently hold off on irrigation longer than they used to, improving their opportunity to catch a rain to replace part or all of an irrigation, but still having time to irrigate before crop moisture stress if it doesn't rain in time.
About a dozen miles from the Valentines' fields, Traudt operates seven pivots with the sensors. He estimates he saved at least $1,200/circle last year. Sensor readings have given him the confidence to hold off on irrigating when he might otherwise have jumped the gun. In a wet year, it's even more difficult to know where you are on soil moisture than when it's dry, he feels.
“This last year, we saved one and one-half to two circles (irrigations) per pivot,” Traudt says.
Traudt says the sensors and ETgage help him determine when to schedule the last irrigation of the season. His goal is to leave about a 40% moisture deficit to take advantage of fall rainfall to fill the root zone.
Stahr sees the most potential for payoff from this technology at the beginning and end of the irrigation season — when to start and when to stop watering.
The tendency is to “typically err on the side of making sure we are not short (of water), says Gary Zoubek, York County Extension educator who has worked with irrigators using the technology in his county. “But, Suat's data shows in our area, in many cases, we just don't utilize all of the water stored in the soil, especially at the end of the season.”
DON'T FORGET THE ATMOMETER
All of these Nebraska irrigators — Dennis Valentine, Hastings; Walt Traudt, Clay Center; Jerry Stahr, York; and Gerry George, Waco — use another piece of technology to help them with their scheduling: an ETgage. The patented atmometer measures evapo-transpiration, which mimics how much moisture is given up by the crop through evaporation and transpiration.
While the soil-moisture sensors tell these irrigators how much soil moisture has been depleted, the ETgage lets them see how fast the crop is using water on a daily basis, which helps them know how long they can safely hold off irrigation in anticipation of a rainfall. “It's good checks and balances,” Traudt says of the ETgage.
Stahr agrees. While either one — sensors or ETgage — can work for scheduling, they work best in conjunction with each other, he says.
HOW IT WORKS
The new sensors, like gypsum blocks, are based on how soil moisture level affects electrical conductivity in the soil. But the new sensors are more durable and reliable. And, readings from the improved sensors for irrigation scheduling are further simplified by an easy-to-use system developed by Suat Irmak at the University of Nebraska-Lincoln (UNL). From a table of moisture readings for various soil types (varying soil water-holding capacities) that he devised from his documented research results, an irrigator can apply a moisture reading to the table for a direct answer on whether to irrigate.Continue on Page 2
Fifty irrigators who completed 2007 questionnaires about their use of this technology reported an average savings of 2.6 in. of water/acre on corn and 2.1 in. on soybeans that year. That amounted to pumping cost savings of $24/acre for corn and $19.40/acre for soybeans on a typical center-pivot installation with diesel-powered pumping that year, says Irmak, soil and water resources engineer at UNL. Even at this past winter's lower diesel prices, the savings would come to roughly $13 and $11/acre, respectively. (Collection and tabulation from a survey for the 2008 season are underway.)
Here's how the system works. Soon after crop emergence, a sensor is placed at each of three depths — 1, 2 and 3 ft. — within the crop row, in a representative part of the field. Generally, only one set of sensors is needed per field per crop, as long as the soil type and slope are generally uniform.
For each depth, a corresponding length of PVC pipe with a 1-in.-diameter Watermark sensor glued to the end is used to push the sensor to the bottom of the hole made by a ⅞-in. probe. The tight fit of a 1-in.-diameter sensor in the ⅞-in. hole ensures soil contact with the sensor. Placement early in the season avoids disrupting crop roots that will grow around the sensors to ensure an accurate measure of soil moisture uptake by the crop.
Electrical wires leading up through the PVC tubes are attached so that soil-moisture readings can be taken by either a handheld meter carried from field to field, or by a data logger that remains in the field, hooked up to the sensors for continuous soil-moisture readings.
A reading from either is lined up with the appropriate soil-type column in the table, which lets you read directly from the table the water depletion, in inches per foot of soil, for your field's soil type.
To simplify further, the table includes the readings at which irrigation is recommended for each of the eight different soil types. Those recommendations are based on irrigating when approximately 35% of the soil's water-holding capacity per foot in the top 2 ft. has been depleted during vegetative stages of growth and the top 3 ft. during crop reproductive stages. “This table is the brain of what we do,” Irmak says.
Sensors cost $25-30 each and can be used at least five years, Irmak says. (A twist of the PVC tubes with Vice-Grips helps pull them up at the end of the season.) A handheld meter costs $230-250 and a data logger costs $300-325, Irmak says. The data logger can be purchased with the optional capability of being read remotely by telemetry up to 15+ miles away, according to Irmak.
For more details and videos of how these sensors are installed and used, go to http://water.unl.edu, click on Agricultural Irrigation, and then on Nebraska Agricultural Water Management Demonstration Network. Under that heading is a menu for viewing videos of use of the ETgage and Watermark sensors, as well as information on the water management demonstration network.