AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Summer 1996, No. 2
Many plant products high in protein are also high in potassium. Examples include high protein alfalfa forage, and high protein soybean seed, in comparison with the relatively low protein and potassium concentrations of corn and cereal grains. But does this relationship between protein and potassium have any significance for the level and quality of protein in wheat?
In contrast with nitrogen, potassium does not become a part of the protein molecule. However, whenever proteins are made or broken down, ample supplies of potassium must be present to facilitate the reaction. A substantial amount of the protein in the wheat grain comes from protein broken down in the leaves and stems and transported to the grain. Potassium facilitates the breakdown, the transport and the synthesis of proteins. It also stabilizes proteins for storage.
Experiments have shown that potassium can increase wheat protein concentration by enhancing the translocation of nitrogenous compounds from vegetative plant parts to the grain. In doing so, the availability of amino acids for grain protein synthesis is increased. In some experiments, however, potassium enhanced grain yield even more than total nitrogen uptake, and the resulting dilution can lead to lower grain protein concentration.
Almost all of the potassium uptake in wheat occurs before heading. In fact, total potassium content often declines between heading and maturity. Since uptake is very rapid, adequate potassium supply from the soil is important. Plant uptake of potash is about equal to the uptake of nitrogen in wheat grown with intensive management for high yields.
Potassium should be an integral component of any soil fertility program for intensive cereal management for bread wheats. When nitrogen is applied at higher levels in order to boost yield and protein, potassium counterbalances the increased risks of lodging and disease. One study found that high nitrogen uptake with insufficient uptake of phosphorus, potassium and magnesium produced wheat of poorer baking quality, in spite of high protein contents. The need for balanced fertility increases with intensive management.
The choice of potassium fertilizer material must also consider the chloride and sulfur nutrition of the wheat crop. In areas where sulfur limits the yield and protein level of wheat, sulfate of potash may be the material of choice. In many parts of the Great Plains, chloride has been demonstrated to have a role in promoting yield and minimizing disease in wheat crops. In these areas, potassium chloride may be preferred. Interactions with magnesium are often important for potassium nutrition. When soil magnesium levels are low, sulfate of potash magnesia may be the potassium source of choice.
Remember, potassium is the facilitator for protein. It’s no coincidence the two are related. If protein is a goal of your intensive cereal management, include potassium in the package.