Time to Rethink Your Water Program

Time to Rethink Your Water Program

Test plot research shows consistent yield gains using variable-rate irrigation

Water is often top of mind this time of year, whether battling too much or too little in fields. In recent years, irrigation pivots have sprung up across the countryside, drastically changing the concept of water. To keep  in tune with the latest irrigation technologies, the Farm Journal Test Plots  have been studying variable-rate irrigation (VRI) methods. 

Calibrate pivots to ensure nozzles are in working condition and to verify target water rates are being met in different management zones.

In partnership with Valmont Industries Inc., the test plots crew installed a Valley VRI system to efficiently apply water to natural management zones within a field. The system was outfitted on a pivot owned by Dan Meeker in Mason County, Ill. The VRI system uses existing electrical lines on a 1,296' half-circle pivot to send signals and information along the span. 

The three-year study consists of an 80-acre field with soil types that range from sandhills to loams. The soil types include Canisteo silty loam, Selma loam, Onarga sandy loam, Sparta loamy sand, Ridgeville fine sandy loam and Gilford fine sandy loam. To cater to the various soil types, the pivot was outfitted for Zone Control, which allows for prescriptions to vary by management zone.

“Our goal was to collect years of yield data to see if we can predict how much water it takes to maintain yields on certain soil types,” says Farm Journal Field Agronomist Ken Ferrie. 

This thermal image shows the temperature of the crop. The green areas are receiving adequate water, the red and white areas too little and the purple and blue areas too much water. 

In its first year of study in 2012, the Farm Journal Tests Plots crew learned each zone or soil type was not getting the appropriate amount of water using a standard center pivot. The sandhills require more water than the bottom loams, but without VRI, there is no efficient way to cater to the specific needs of soil types. 

To more effectively use the VRI system, the following year, the test plots crew conducted a water infiltration test with equipment available from Cornell University. Test results found the infiltration rate in the bottom loams was twice as much as the sandhills. This was opposite of what the crew assumed for the given soil types. In this particular case, soil characteristics trump gravity. 

“We realized in our soil moisture data and infiltration tests that more water across the board wasn’t the issue; it was the amount of water each zone was receiving per watering,” says Isaac Ferrie, who oversees the project. 

With this knowledge, the  test plots crew altered the prescriptions to make sure the actual watering rate matched the infiltration rates of each zone. Based on data and in-field evaluations, the VRI prescription was altered to cut back on application rates but apply water more often. 

Across all three years of the study, the loams received an average 7.8 bu. increase, and the sandhills received an average 34.7 bu. increase. The VRI and non-VRI sandhills received the same amount of water, but the water was applied more efficiently. The VRI loams received less water compared with the non-VRI loams, yet yields increased in both areas using less water more frequently. 

To monitor and fine-tune prescriptions, the test plots crew used a variety of methods. A series of thermal images from AirScout and normalized difference vegetation index (NDVI) maps provided by GeoVantage helped the test plots crew dial in and apply the amount of water each zone needed. 

“The thermal images show us crop temperature, and the NDVI maps measure crop biomass,” Isaac says. “We found cooler crop temperatures and higher biomass levels correlate to higher yields.”

Irrometer soil moisture sensors were also used as a monitoring tool to gauge how much water each zone requires. The sensors were placed in a representative zone for each of the primary soil types at three depths—6," 18" and 24"—then networked to a modem in the field that wirelessly transmitted the data to the test plots crew. 

The project gathered well-rounded data thanks to Mother Nature—from one of the worst droughts in 2012 to ideal growing conditions in 2014. 

“In 2012, even at the highest watering rate, some areas didn’t receive enough water,” Isaac explains. “The 
pivots couldn’t run fast enough to apply adequate water to some areas.”

Despite the difficult conditions, the test plots team and farmer continued the study, which paid off in valuable baseline information.

“In a drought, there is still only so much water you can apply in a day,” Ken says. “When it got too hot, we had corn plants abort ears, and if an area is lost to the drought, no matter how much water we apply, we might not bring it back.”

As this multiyear effort comes to a close, the Farm Journal Test Plots will continue to study cutting-edge irrigation technologies. 

By altering application rates and frequency, the silt loams received an average 7.8 bu. increase with 5.5" less water in certain years. Likewise, the sandhills received an average 34.7 bu. increase in certain years using the same amount of water. 

What Ken Ferrie Thinks You Need to Know

  • The VRI prescriptions were altered to cut back application rates but apply water more often. 
  • Match the actual watering rate to the infiltration rates in each zone.
  • Use VRI technology in conjunction with in-field scouting to help prioritize water schedules in extreme weather conditions. 

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You can count on our test plots to be conducted on real farms with real equipment using a high-touch set of protocols. The information will be completely independent and actionable. Our hands will always be in the dirt researching the production practices and technology that are best for you. To learn more, visit http://www.FarmJournal.com/testplots


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