Soil moisture sensors

The Grevings are experimenting with wireless soil-moisture sensors, which measure changes in soil water content in the root zone. In 2013, Jeremy tried a McCrometer Connect capacitance soil-moisture sensor with wireless telemetry in one soybean field. The probe monitored soil moisture from 6 inches to 3 feet deep, transmitting the data to Jeremy’s iPad.

In other fields, he employed an irrigation scouting service. “Where the agronomist was telling me to apply 1 inch of water, the McCrometer was telling me to speed up the pivot a bit,” Greving says. “I could see the water was soaking in really well in that field and the crop wasn’t using a whole inch.” So he cut the application rate in that field to 0.70 inch per revolution.

“When we got rain, I started the pivot a day or two later than I normally would have because I had the sensor to tell me I still had moisture in the soil. That was real beneficial, knowing when to start back up again after a rain.” He estimates that having a sensor in the field let him cut water application by about 25% in 2013.

One of the limitations of soil-moisture sensors is placement, says Tom Scherer, an agricultural engineer at North Dakota Extension. “Were do you put them? You have 130 acres under the pivot,” so finding a representative location is essential.

It’s a good idea to check soil water conditions in other areas of the field with a hand probe and compare to the sensor readings, says Chuck Burr, an Extension irrigation specialist in west central Nebraska.

Burr also recommends atmometers, which estimate actual crop water use — or evapotranspiration (ET). You read the ET gage on a weekly basis, then compare how much water the crop has used to the amount of rainfall and irrigation the field has received for the past week.

Variable rate irrigation

One water-efficiency technology that’s coming on very strong is variable rate irrigation (VRI), says Scherer, the North Dakota engineer. Quandt is using VRI zone control in two fields where sprinkler water collects in low spots and clay pockets. He puts together watering prescriptions for each 50-foot section of pipe. In zones prone to pooling, banks of sprinklers pulse off at prescribed intervals, reducing water application. That cuts overwatering and runoff, as well as N loss from leaching, Quandt says.