Soybeans and Potassium

Potassium’s primary plant function is to regulate the direction of water flow between cells and different plant tissues.  The xylem and the phloem, which is the plants “plumbing,” relies on potassium to direct its direction of flow.  The xylem moves water and nutrients upward and outward while the phloem moves sugars and water downward toward roots. Just as in your home plumbing, higher pressure in one plant region (like your water main) will push sap towards areas of lower pressure (like an open faucet)

Leaves act as solar panels that are switched on during the day.  Just as a lightning rod absorbs static electricity and harmlessly channels it to ground, leaves depend on converting potent solar energy to sugars that can be safely transferred and stored. Plants absorb sunlight which is converted to energy via photosynthesis. The plant uses water – H2O + C – carbon from carbon dioxide in the air to make plant sugar or sucrose – C12H22O11. Plant sugars are then respired at night through chemical reactions in the plant to fuel plant and seed growth. The ultimate goal of a plant is to simply produce as many potential offspring as possible. Our goal is to manipulate the plant into producing large numbers of offspring and have the offspring be as large as possible.

Potash soil test levels have widely declined during the past several years, and need to be more closely monitored. Growing conditions that limit uptake of nutrients include reduced root mass from excessive soil moisture early for some and periods of very dry soil where potassium and other nutrients are held tightly to the soil and thus are not available for plant uptake. Potash is a mobile nutrient in the plant so deficiencies typically show as yellow tips at the lower leaves of the plant. One interesting aspect is that aphids love beans that are low in potassium levels. It is very common to the largest aphid populations on soy plants with low K levels.

If you are witnessing these conditions in your crop, what can you do?  Consider a foliar fertilizer that directs potassium directly to plant leaves.  Often, it is tempting to reduce foliar fertilizer cost by focusing on one or two nutrients.  Effective fertilization, however, depends on having adequate potassium to distribute sugars (and foliar nutrients) to other plant parts.

Don’t stand by while your soybeans go into shock.  Give them a shot of potassium with their next foliar feeding.