Conventional wisdom has long held that farmers should stop irrigating soybeans when the beans are “touching” in the pod.
New research and field observations are showing that terminating irrigation when the soybeans are merely touching may mean at least one more irrigation is needed, says Trent Irby, Extension soybean specialist with Mississippi State University.
But that can also depend on how much moisture is in the soil profile, according to Jason Krutz, Extension irrigation specialist with MSU. Drs. Irby and Krutz talked to farmers about determining when to stop irrigating their crops in a series of Turn-Row Irrigation meetings in the Delta Aug. 26.
“At (growth stage) R-5.5, if you took that pod and looked at the seed, about half that space would be filled up,” said Irby. “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.”
That’s the point where growers want to make sure they have enough moisture in the soil to get to that stage, according to Irby and Krutz, who conducted their “Turn-Row Irrigation Termination sessions at stops at the Richy Bibb Farm in Tunica County, the Delta Research and Extension Center at Stoneville and the Reese Pillow Farm in Leflore County.
The sessions were sponsored by the Mississippi Soybean Promotion Board, Mississippi State University and members of the Detlta Sustainable Water Resource Task Force.
“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.”
If the specialists think they have enough moisture in the soil to carry the soybeans to the R-6.5 stage, then “we can walk away from this field without having to send another irrigation shot down the field,” says Krutz.
For more about irrigation in the Mid-South, see http://deltafarmpress.com/irrigation-technology/variable-rate-irrigation-featured-milan-no-till-field-day.