Foliar feeding Not effective
Foliar feeding soybeans doesn’t usually increase yields, says Ron Gelderman, South Dakota State University Extension soils specialist.
“In general, foliar fertilization has not proven effective unless there is severe deficiency of a particular nutrient,” he says.
One bushel of soybeans requires about 4.9 pounds of nitrogen, 1.1 pounds of phosphorus, 2.4 pounds of potassium and 0.4 pound of sulfur.
Micronutrients such as zinc, iron, manganese, copper and boron are taken up as a fraction of a pound per acre.
“The amount that is actually needed is less than what is taken up in most cases, but those levels are not well defined because micronutrient deficiencies in soybean are rare — especially in South Dakota with our relatively high-fertility soils.”
Because of the large need for macronutrients, foliar application is usually not considered. Macronutrients are better applied as a soil application.
“In high soybean yield situations, there is some evidence that N added in-season at about early pod, (20-30 pounds per acre) may be beneficial but the uptake of the applied N is mostly from the soil rather than foliar,” he says.
In South Dakota, there have been foliar fertilization studies on 14 soybean sites, three corn and two small-grain sites over the past 35 years. These studies had multiple treatments covering almost all the macro, secondary and micro nutrients. Of these studies, Gelderman says there was only one positive response.
“That was added foliar P to very P-deficient corn. There were four treatments that caused yield declines, either from leaf burn or other unknown causes,” he says.
Gelderman says there has also been an increased interest in adding manganese with glyphosate applications to soybean. He says most of these positive responses took place in Indiana on soils with very high organic matter and high pH. “These are soils on which we would anticipate a micronutrient deficiency. These soils are not found in South Dakota,” Gelderman says.
“Unless a rescue operation is needed, most nutrient applications should be done prior to or at planting.”
This article published in the September, 2012 edition of DAKOTA FARMER.