Soil type determines soybean irrigation decisions

Frances Gould, Morgan, Johnny W.  |  10/21/2014 11:33:13 PM

LSU AgCenter agronomist Josh Lofton looks over soybeans in his research plot at the Macon Ridge Research Station near Winnsboro. Lofton said this is the second year of the study, and he is finding that soil type is a major factor when making irrigation decisions in soybeans. The light soils on the Macon Ridge tend to need much more water than soils at the Northeast Research Station in St. Joseph. (Photo by Johnny Morgan)

Moving into the second year of data collection for his soybean irrigation study, LSU AgCenter agronomist Josh Lofton says soil type is a major factor in irrigation decisions with soybeans.

The two objectives of the project are to look at how irrigation is managed in soybeans and how management in soybeans differs depending on whether you’re farming light soils, like on the Macon Ridge, or in heavier soils, like those found across the Mississippi alluvial valley.

Trial locations are at the Macon Ridge Research Station and at the Northeast Research Station at St. Joseph. Both of these areas are known for soybean production. The difference is the amount of water needed to produce the crop.

Lofton wants to find out the optimum time to apply irrigation to obtain maximum benefit.

"Essentially we are continuing the project we started last year," Lofton said. "That’s because we found a lot of good results last year in the project."

The project consists of four different timing sequences for irrigating the soybeans at each location, he said. "

The first application of irrigation water is applied when they are planted, then at four or five trifoliates, which is near the end of the vegetative stage," Lofton said. "Then again at mid-flower, what growers call R2 to R3, and finally at pod set, which is our current recommendation, as well as a late-season irrigation at seed fill."

Lofton said economics is the determining factor in most decisions about irrigation.

Last year was a wet year, and that presented some challenges and limited the benefit of some of the earlier irrigations, Lofton said.

"In the alluvial soils, we started irrigation at pod set, and we lost no yield," he said. "We had a tremendous amount of moisture in early season last year, and we only applied one irrigation between flowering and pod set, where in most years you need more.

"You could delay irrigation until pod set in soybeans at St. Joseph in those deep Mississippi alluvial soils," he said. "But that was not the case at Macon Ridge."

Lofton said there was the possibility of yield loss if you waited until pod set, as well as losing yield if you waited until flowering.

"So we needed to be irrigating during late vegetative stages to reduce significant yield loss," he said. "In really hot, dry years, we probably needed to have watered at least once during this stage."

So far, the project has later irrigations in the St. Joseph area, which means farmers don’t have to turn on those expensive pumps as often as on the lighter soils.

"You can definitely save yourself one or two irrigations on those deep Mississippi soils," Lofton said. "But you can’t do that on the light soils at Macon Ridge when it starts to get hot and dry."

The bottom line is what the grower is interested in, and to this point in the project, St. Joseph appears to be the area requiring the least irrigation to harvest a good crop.

"Without irrigation, we achieved 30-40 bushels at St. Joseph, but we only got about seven bushels at Macon Ridge," he said. Johnny Morgan

This article was published in the 2014 Louisiana Soybean & Grain Research & Promotion Board Report.

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