It was almost the irrigation season that wasn’t for corn and full-season soybeans in the Mid-South and Southeast in 2014.
Mid-South corn growers, accustomed to having to water their crop four, five or six times, laid out poly tubing but only had to turn on their pumps once or twice. Some wished they hadn’t for at least one of those.
“We had some farmers in the central Delta who saw leaf curl in their corn and decided to lay out their polypipe and irrigate,” says Jason Krutz, Extension irrigation specialist at Mississippi State University. “Two days later, they got a seven-inch rain.”
Krutz says he can understand why growers would be anxious to begin irrigating given how much is riding on their crop.
“We start seeing cracks like this; it hasn’t rained in seven to 10 days; we see a little leaf curling; and we panic and start irrigating,” he said during a discussion with members of the Delta Water Resources Task Force in a field on the farming operation of Tim Clements and Ted Smith near Greenville, Miss.
Clements is one of several growers Krutz is working with to help improve irrigation efficiency, reducing costs and conserving water, an increasingly precious commodity in the Mississippi Delta.
Sensors are useful tools
One of the tools Krutz uses is a sensor that provides readings of soil moisture at depths of six, 12, 24 and 36 inches. Being able to drive up to a field, find out how much moisture the crop has available to the root system at varying depths can help farmers know when and when not to irrigate. Krutz refers back to the heavy rainfall event last spring:
“A lot of our producers held up on irrigating, and our consultants were smiling because the sensors were telling them they still had moisture. Then we saw there were big clouds over in Arkansas. We knew we had five or six days before we had to turn on the wells. Using the sensors allowed the clouds to get there and rain.”
Clements was also using a program called PHAUCET (pipe hole and crown enhancement tool) to help match the water flow from his irrigation tubing to his fields. Last spring, Krutz persuaded him to try a surge valve, as well.
Surge valve aids water penetration
“Using a surge valve helps the grower get better penetration of the soil profile because it sends pulses of water down the rows,” he said. “The water has time to soak into the soil in one area before another surge of water comes down the row.”
On one farm in 2013, the grower was never able to irrigate one of his fields completely because he couldn’t get water to run from his irrigation pipe to the other end of the field even when operating the pump around the clock.
“He went back to look at his yield data, and he said that over the last several years, this field is usually about 10 bushels per acre behind the other ones,” Krutz said. “That makes sense because he’s not irrigating the bottom third or fourth of the pad.”
Krutz and his coworkers installed surge valves on the irrigation pump, set the grower up on the PHAUCET program and installed moisture sensors at the six-, 12-, 24- and 36-inch depths in the problem field.
The producer irrigated five times with 12.85 inches of water and harvested 87 bushels of soybeans per acre in one corner and watered five times with 14.9 inches of water and cut 85 bushels in another.
“This is the problem set,” said Krutz, displaying figures for the upper right quadrant of the field. “We get across it. It takes a little bit of time, but we do it. This well sits idle part of the season.
“We put three shots out with a total of 9.4 inches and cut 86 bushels per acre. On our other 40-acre set, we gave it three shots with about 7.2 inches of water and cut 84 bushels.
“So if you look at it just for this year alone, we’re about a bushel per acre behind, profitability is about equal, and we did it with about 40 percent less irrigation water. In reality, we probably did it with half the water.”
Using more precise irrigation methods also is being extended to the end of the watering season.
Avoid terminating too soon
For corn, experts worry that farmers may stop irrigating too soon and reduce yields. Most agree corn may need irrigation until it reaches the black layer stage. For soybeans, growers can stop watering when the soybeans reach R-6.5.
“At (growth stage) R-5.5, if you took that pod and looked at the seed, about half that space would be filled up,” says Trent Irby, Extension soybean agronomist for Mississippi.
“When you get to R-6, that seed is touching – we like to call that knuckled up. The seed will almost be flat on the edge where it’s full. That cavity will be completely filled up with seed. R-6.5 is when that seed completely separates from the protective membrane in that pod.”
Growers should make sure they have enough moisture in the soil to get to that stage, according to Irby and Krutz, who conducted a series of “Turn-Row Irrigation Termination” sessions in the Delta in late summer.
“When we make termination calls, Trent is looking for those pods in the upper four nodes,” said Krutz. “I’m going to come in with a portable soil moisture sensor, check the soil profile.
“Then we’ll start a conversation about how many days you think it will take to get from whatever growth stage he’s seeing in the upper four nodes to that R-6.5 point.
“Then I’ll put the portable moisture sensor in the soil profile and take an estimate of how many days of moisture I think we have.”
Researchers at the University of Georgia are also using precision farming tools to conserve water.
Yield maps are helpful
A yield map, says George Vellidis, UGA crop and soil sciences professor, can readily show the changes in yield that result from various water patterns in a single field. For example, bright green circles within a field can pinpoint leaks in a center pivot.
“While a yield map can show us that more water resulted in more yield, it also can show us that a field is being under-irrigated. That’s not really a surprise,” says Vellidis.
“These kinds of yield maps provide us with an interesting opportunity. Because not only can we see that the yield increases with additional water, but we can make economic decisions from this data. You can see how much more yield resulted from the extra water, and you can see if it would be economically beneficial to irrigate at the higher rate.”
Many of the commercial center pivot manufacturers are now offering VRI systems that work with their panels, says Vellidis. There are also systems that can be retro-fitted onto pivots from different manufacturers.