Is lack of potash holding back your soybean-wheat system?Is lack of potash holding back your soybean-wheat system?
Virginia soybean farmers need to make sure they are applying enough nutrients to their crop to achieve maximum yields. Potash is important while sulfur deficiency is now showing up in the commonwealth.
August 16, 2017
Virginia soybean farmers need to make sure they are applying enough nutrients to their crop to achieve maximum yields. Potash is important and sulfur deficiency is now showing up in the commonwealth.
Mark Reiter, assistant professor of soils and nutrition management at Virginia Tech’s Eastern Shore Agricultural Research and Extension Center in Painter, says producers aiming for 60 bushels per acre soybeans and 100 bushels per acre wheat in a soybean-wheat system, need 411 pounds of potash to be available to both crops. “Most of it is in the soil, but farmers need to put out 80 to 120 pounds of potash depending on the soil,” he explains.
Reiter spoke at the Virginia Ag Expo held at Renwood Farms in Charles City, Va. on Aug. 3. Renwood Farms is owned by the Stanley Hula family and is the site of the world record corn yield of 532 bushels per acre produced by David Hula in 2015. In addition to producing corn, the Hula family produces soybeans and small grains on more than 6,000 acres on the James River in southern Virginia.
At the expo, Reiter said determining potash needs is critical for achieving maximum yields in a soybean-wheat system.
“If you’re removing 60 bushels of beans, you’re actually removing 84 pounds of potash. In wheat, if you’re just removing the wheat grain, you’re actually removing 34 pounds of potash, so in the soybean-wheat system you’re removing 118 pounds of potash. To keep all things equal, how much fertilizer do you need to put out? At least 118 pounds. For high yielding systems you need more,” Reiter said.
In the meantime, Reiter said he is seeing more sulfur deficiencies in soybeans across Virginia. He attributes this to the Clean Air Act that has greatly reduced acid rain. In 2000, crops received about 20 pounds of sulfur per acre from rain; today it’s less than two pounds. Most soybean plants need about 30 pounds of sulfur per acre..
At this time, Virginia Tech has no official sulfur recommendations, but Reiter is conducting research at the Hula farm and other locations where he is applying 10, 20, 30 and 40 pounds of sulfur per acre from gypsum or calcium sulfate.
Depending on what area of the state they farm and their soil types, there is likely 20 to 30 pounds of sulfur in the soil 20 inches below the surface. “If your roots can’t get to it, you’re probably sulfur deficient,” he said.
Reiter noted that the Hulas have plenty of sulfur in their sandy loam soils.
Turning to soybean varieties, Virginia Extension soybean specialist David Holshouser, after evaluating 10 years of data at five locations across Virginia of both double-crop and full-season beans, says Group Vs tend do best in southern Virginia while group IVs tend to perform better in the northern part of the commonwealth.
“The yield potential can be quite substantial during bad years when you pick the wrong maturity group,” Holshouser said.
As far as seeding rates in Virginia, Holshouser’s standard recommendation for full-season soybeans is 80,000 to 90,000 plants per acre.
“To get that need to be putting out about 90,000 to 110,000 seeds per acre. We can probably go lower on that on a good soil. On soil under irrigation, I feel comfortable going down to 80,000 seed per acre,” he said.
On poor soils, a rate of 120,000 to 140,000 seeds per acre works best.
David Holshouser, far left, Virginia Extension soybean specialist says Group V’s tend do best in southern Virginia while group IV’s tend to perform better in the northern part of the commonwealth.
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