Writer: Pam Dillard (806) 359-5401, p-dillard@tamu.edu
Contact: Brent Bean (806) 359-5401, b-bean@tamu.edu
AMARILLO – Farmers in the Texas Panhandle and South Plains have jumped on the soybean bandwagon. Soybean production in those areas has increased dramatically over the last two years, says Dr. Brent Bean, agronomist with the Texas Agricultural Extension Service.
According to Bean, Texas soybean acreage grew from 290,000 in 1996 to 420,000 in 1997. This can be partly attributed to the loss of cotton acreage in the South Plains, Bean said. Other factors that led farmers to make the switch included poor early season weather conditions and boll weevil concerns.
Bean said the availability of Roundup Ready herbicide- resistant soybean varieties also has helped producers make the change. Using Roundup in soybeans appears to help effectively control or suppress weeds that producers were less able to control in other crops.
In the past two years, a few producers have been successful in growing dryland soybeans, said Bean. Yields have generally ranged from 15 to 20 bushels an acre with an occasional jump to 25 bushels per acre. With these kinds of dryland yields, soybeans will compete favorably in most years with wheat or sorghum, he added.
Bean also cautioned producers to check rainfall histories in their area for 1996 and 1997 when considering crop selections. Weather conditions were very favorable for soybean production in those years, he said.
For example, in 1996 more than 16 inches of rain fell from May 1 to Sept. 30, with nearly 5 inches falling in August. Although 1997 was drier from May 1 through Sept. 30, almost 3 inches of rain was received, again in the critical month of August.
The agronomist also cited studies in 1982 and 1983 by Dr. Harold Eck at the USDA Agriculture Research Center at Bushland, which showed the importance of rainfall and irrigation timing on soybean production. Seasonal rainfall in 1982 was 15.3 inches but in 1983 only 6.4 inches.
As a result, soybean yield was much higher in 1982 compared to 1983 regardless of irrigation, he added. In 1982, the wettest year, production reached 30 bushels an acre with no irrigation. By contrast, with the drier conditions in 1983, soybean yields fell to six bushels per acre, even when irrigation was used early in the season.
This study demonstrated the importance of water that the plant must have for grain fill, which typically occurs in August, Bean added. In both years, rainfall was less than one inch during August. When irrigation was not applied during the critical grain-fill period, yields were greatly affected.
In 1983, if a single irrigation treatment was missed during this period, yields were reduced 22 bushels an acre. Even in 1982, when rainfall early in the season was abundant, yield was reduced 29 bushels per acre when one irrigation was skipped during grain fill, he said.
According to Bean, soybeans can be stressed early in the season without greatly affecting yield. However, if the soil profile is allowed to dry out it may be difficult to provide adequate water necessary to prevent the crop from being stressed later in the season, he said.
Soybeans have a taproot system, allowing the plant to capture moisture from a depth of 5 feet, he said. This ability to use deep soil moisture diminishes the need for frequent irrigation.
Bean also pointed to research by Dr. Bill Lyle at the Texas Agricultural Experiment Station at Halfway, which found no difference in yield for soybeans that were watered on a 3.5-day schedule compared to ones watered every 14 days.
Farmers should keep in mind that the demand for full irrigation on soybeans, as with any crop will vary from year to year, he said.
In 1995 studies by Dr. Terry Howell at the USDA research station at Bushland, yields topped in at 68 bushels an acre when irrigation was based on evapotranspiration demand. These fully irrigated beans required 20 inches of irrigation water, or about 85 percent of the irrigation water needed by corn.
Because peak water use for soybeans occurs in August and early September, they make for a good rotation crop with corn, particularly short-season corn, said Bean. As the peak water demand for corn begins to decrease, that’s when irrigation resources can be diverted to soybeans.
A soybean-corn rotation will give producers an excellent opportunity to clean up weeds, and break insect and disease cycles that can build up in continuous corn systems.
Last year, one local farmer showed a 13-bushel increase in corn yield on his half circle following soybeans when compared to the same half circle planted to corn the previous year, said Bean. The difference was attributed to less insect pressure in the corn grown after soybeans.
Soybean rotation with cotton or sorghum isn’t as viable, from an irrigation scheduling stand point, since the periods of maximum water use are virtually the same for these crops.
If adequate water is available, double cropping behind wheat is a good option, said Bean. Soybeans can be planted as late as July 5 and still produce satisfactory yield.
In 1996 and 1997, some farmers realized 40-bushel yields when beans were planted in the first week of July. However, for every day past about June 20 that planting is delayed, yield will generally be reduced one bushel per day, the specialist said. Even the potential for an early freeze cannot be discounted, which can dramatically reduce yield in late-planted soybeans.
For more information on growing soybeans, Bean recommends contacting the local county Extension office.
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