Plant & Soil Health: Importance of Potassium in Soybeans

Soybeans have a big appetite for potassium, so ask yourself, are you feeding them enough?

Soybeans require potash and plenty of it and remove more than corn. A 200-bushel corn crop will remove 50 lbs. of potassium per acre, while an equivalent 70-bushel bean crop will remove 84 lbs. How much attention do you pay to making sure potash levels are adequate before you plant your soybean crop?

Many growers have routinely applied fertilizer before two successive crops of corn and let their soybeans scavenge for leftovers. We all know what happens to pigs that become the runts of a litter—they always get the leftovers and remain small their entire lives.

The problem with potassium is that what you apply is not necessarily readily available to the second-in-the-rotation soybean crop, especially 18 months after you apply it. When managing your potassium program, consider the following:

• Potassium is relatively immobile in the soil, so availability depends on location and soil characteristics.
• No-till and minimum tillage methods, as well as compaction, can limit root growth and access to potassium.
• No-till can stratify potassium near the surface, above the root zone.
• Soil temperature, pH and moisture impact potassium availability.

Potassium is most available at a near neutral pH from 6.0 to 7.0.  Soil moisture is essential for potassium to move in the soil to the roots and in dry years it can be limiting. Cool spring temperatures can also limit root grow and mineralization, creating temporary shortages.

Availability of soil potassium depends on the type of clay. Soils that have high clay content retain potassium in their soil lattice structure.  What is the best strategy for managing potassium?

• Make sure soil test levels are moderate to high so your crops never experience shortages.
• Fertilize before each and every crop and apply removal rates.
• Manage for ideal soil conditions to maximize potassium availability.
• Foliar feeding potassium in season is practical and efficient.

How do you manage your potassium fertility program in soybeans?

Let us know in our forums how you approach potassium recommendations and how/if you apply potash before soybeans.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.