Plants require potassium (K) because it promotes stalk health, balances anions such as nitrate and sulfate, regulates plant water relations, and activates enzymes that promote healthy growth.
Most soils require more K, but soil types vary.
Weathering causes certain soil minerals or parent material to release more K than other soils. Furthermore, some clays can bind K between clay layers. Because coarse-textured sands can leach, their critical soil test K values are lower than those of medium- and fine-textured soils.
Corn and forages consume more than 100 pounds of K per acre and up to 200 pounds of K per acre. Most K remains in the forage, whereas grain removal of K is relatively low in corn and higher in soybeans.
These five suggestions will help farmers maximize the return on investment from their K treatments.
1. Don’t Overapply Phosphorus.
Farmers occasionally overapply phosphorus (P) to their fields, and each crop removal increases soil test P on neutral and acid soils. As a result, excess P fertilizer costs are spent on K, particularly in the Upper Midwest, with higher ROI potential.
2. Test Your Soil.
Every year, take soil samples in the spring and fall. Please don’t change the scheduling of the tests because it can impact soil test K results, perhaps more than other nutrients.
These factors may have an impact on soil test results:
- Mineralogy of clay.
- The moisture content of the soil at the time of sampling.
- If soil testing is in the fall, crop residue.
Crop leftovers include a lot of K, which takes a long time to drain back into the soil. As a result, sampling in the early fall may yield poorer results than testing in the spring.
3. Use the Correct Soil Test.
Use the appropriate soil test and extractant for your location or state to ensure the most accurate soil test results. Mehlich III and other universal extractants must be calibrated to your state’s K fertilizer standards.
4. Consider Applying K Yearly.
On coarse-textured soils, applying K once a year may be beneficial. This is true throughout the Corn Belt and most likely on low-CEC grounds throughout the country.
5. Pursue Higher K Applications, Where Applicable.
According to the University of Minnesota studies, K treatment rates are more significant than crop removal rates for corn and soybeans, especially on medium testing soils — roughly 100 to 150 parts per million using the ammonium acetate test. Depending on the situation, proper K application may differ.
Some crops, mainly maize, may respond to K-band applications. However, new University of Minnesota research indicates that the yield gain is minimal and may not cover increased costs compared to broadcast applications. However, if you are banding in a strip-till-age scheme, continue doing so because it decreases K stratification. I’ve also noticed yield responses to band treatments over broadcast in reduced-till and no-till environments.
Although potassium does not have the environmental concerns of phosphorus and nitrogen, improper potassium management still impacts ROI. Thus, correct application is critical to getting the most out of the fertilizer.
Learn more: How Frequently Do Farmers Soil Test?