Fall Freeze Takes Toll on Western Kansas Soybeans

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GARDEN CITY, Kan. - Typically, some late-maturing soybean fields suffer from freeze damage in the fall, but more soybean acres than normal have been affected this year in western Kansas, according to Kent Martin, crops and soils specialist with Kansas State University´s Southwest Area Extension Office.

Temperatures fell to 24 degrees Oct. 10 in Garden City, 20 degrees at Tribune, and 20 degrees at Colby, he said. For much of western Kansas, the earliest killing freeze occurred Oct. 3.

"This caused many late-maturing plants to die before the seeds were fully developed," Martin said.

Temperatures in the range of 30 to 32 degrees damage soybean tops, the agronomist said. Wisconsin data show that 80 percent of soybean leaves were damaged after five minutes at 26 degrees.

While freeze tolerance may be slightly higher in thick stands and narrower rows, Martin said, the Wisconsin research found that yields were reduced when frost occurred at or before R6 (the stage at which seed fills the pod cavity at one of the four uppermost nodes). The most sensitive growth stage for economic yield loss was the R5 (seed 0.3 centimeter long at one of the four uppermost nodes).

Yield reductions occur as a result of a reduction in number of beans per plant and reduced bean size, he said. The maturity of freeze- damaged soybeans is never delayed, but can be accelerated.

"Soybean seeds that are soft and green at the time of the freeze will shrivel, but those in pods that have turned yellow may still mature normally," Martin said. "Clearly, green soybeans are undesirable because of low seed quality and yield, as well as poor end-use qualities. Green soybeans result in off-color meal and oil. They have to be refined out of the oil because of high levels of free fatty acids, which can cause the oil to become rancid."

Martin outlined the options producers have with green soybeans.

* Feeding to cattle - If the soybeans are not moldy, they can be fed to beef cattle if introduced slowly. They should not be fed to young calves that do not have a functional rumen, but can make up to 7 percent of a growing calf´s diet. In a roughage diet, the fat content should be limited to less than 4 percent, which is key in feeding green soybeans to cattle.

* Grazing - The best growth stage for grazing freeze-damaged soybeans is when the plants are in R4 to R5 (full pod to 0.3 cm long seed at one of the four uppermost nodes). The cattle need to have another forage source available, which could include grass pasture, hay or silage. Bloat may be a concern at times, but is less of a concern than with alfalfa or clover.

* Haying or Ensiling - Freeze-damaged soybeans can be a great source of hay or silage for livestock. The best time to harvest soybeans for silage is near maturity, but before leaf loss. When ensiling, producers must add another source of fermentable carbohydrates, such as ground corn grain or molasses (minimum of 10 percent on a dry matter basis), because soybeans near maturity are low in soluble carbohydrates.

"Without the addition of other materials, the silage will have an unpleasant smell and be low quality," Martin said. "Soybeans may be cut for hay at any time because both forage and pods provide digestible protein. Some portions of the hay may not be eaten by the cattle, though, due to refusal -- which can be substantial in some cases."

* Storage - If not sold or fed to livestock, soybeans must be stored. Green soybeans will require special considerations. Note that the soybeans will not lose their green color, although it will be camouflaged after being mixed with other beans. More specifically, aeration does not affect the internal color of green soybeans. But, aerating green soybeans quickly is still very important because of their greater risk of spoilage from mold or insects while in storage.

"During aeration, the grain temperature should be reduced to below 40 degrees as soon as possible," Martin said. "Note that it will take longer to aerate these smaller, immature beans, and make adjustments accordingly. The storage risks for green soybeans are the same as they are for yellow soybeans, as long as they are stored at the recommended 18 percent moisture."

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by: Mary Lou Peter mlpeter@ksu.edu http://www.ksre.ksu.edu/news

For more information: Kent Martin - 620-275-9164 or kentlm@ksu.edu