At the 2018 Fisher Delta Research Center (FDRC) Field Day, Dr. Earl Vories shared his latest research with crop sensor technologies he believes will maximize water use and reduce costs associated with irrigation. “Sensor technologies have advanced to the point where a farmer can more readily benefit from the information coming from the sensor as it relates to crop stress,” says Vories, who is in his 14^th year of conducting research in the diverse soils at the FDRC at Portageville, Mo. “I’m using two kinds of soil moisture sensors in this project: Time Domain Reflectometry Sensors (TDR) and resistance sensors, which are built into a probe that records measurements at five different depths.”

TDR sensors provide readings related to the volumetric moisture content of the soil. “If you’ve got a pint of soil and the water volume is 50 percent, that means you have one-half pint of water in that pint volume of soil,” says Vories. “Resistance sensors measure the tension, or how tightly the water is held in the soil.”

After a rain, readings from these two sensors will move in opposite directions, with the resistance sensor sending a reduced reading because the water is held less tightly, while the volumetric sensor’s reading will scale upward because there is more water.

Sensors and Drones

Vories is using three different types of crop sensors to measure reflectance, height, and canopy temperature. A Holland Scientific ACS 430 reflectance sensor measures in three different wave lengths. “This is an ‘active’ sensor because it has a built-in light source,” says Vories. “You don’t have to be close to solar noon to operate this sensor.”

Passive sensors measure the reflectance of available sunlight but are less reliable on cloudy days. The principle is the same with both sensors — measuring light reflected off the crop canopy. In this case, Vories is using the sensor to measure the red, red-edge, and near infrared portions of the light spectrum.

The Normalized Difference Vegetation Index (NDVI) values calculated from the reflectance give insight about various aspects of the crop like nitrogen needs, chlorophyll status, and water stress.

Researchers continue to benefit from the advantages unmanned aerial vehicles or drones provide. Dr. Jianfeng Zhou, assistant professor, University of Missouri, brought his drone to the FDRC and flew several passes over a field at 160 feet above the ground and was able to then stitch together the acquired digital images to get a complete interpretational image of the entire field. “We also acquire field images from sensors mounted on center pivots, but those only provide a narrow band of field data near the sensor,” says Vories.

An ultrasonic sensor, which works very similar to the way sonar works, sends out a sound wave and a measurement is taken of the time it takes the wave to bounce off the target and back to the sensor. “This allows us to calculate the crop’s height,” says Vories. “This sensor is valuable especially when it comes to PGR applications and certain yield prediction models.”

Vories collects crop temperature data via an infrared thermometer (IRT), also mounted on a center pivot equipped for variable rate irrigation. Temperature readings are taken as the pivot moves across the field. “We can then take those readings and use them to write a variable rate prescription for our next irrigation event,” adds Vories.

One new area of site-specific management Vories is investigating with sensors is providing timely information to breeders. “We hope we can get an indication of a variety’s drought tolerance traits and share that information with our breeders. If a potential new variety responds poorly to drought, that line can be taken out of the development process early, allowing the breeder to concentrate on more promising lines of germplasm,” concludes Vories.