Article written by: Rianne Wagner, Matt Ruark and Shawn Conley
As soybeans are hitting V2-V3 across the state and gearing up to begin their reproductive stages later this month, now is the perfect time to think about potassium management strategies to maximize soybean yield. Soil testing is the optimal way to determine the amount of potassium farmers should apply to their field, however soil tests should have been taken already to guide K applications. If no K has been applied and your expected soil test is in the very low to low range, there are things you may consider when deciding to supplement with K in-season.
Application timing
Nearly 25% of total K uptake occurs before soybeans reach the R1 growth stage, with peak uptake occurring just after R2 (Figure 1). Applying potassium fertilizer before the growing season begins ensures that the nutrient will have time to work its way into the soil and become plant-available by the time it’s needed. Potassium uptake is almost complete in soybeans by R5.5, so any rescue applications of potassium after this point are not likely to reverse K deficiency. Soil testing to guide K applications in the fall or spring has been shown to be the most economically effective approach to managing K.
Figure 1. Potassium uptake rate (pounds per acre per day) in soybean.
Soil Moisture
Potassium is only plant-available when it’s in the soil solution, so there must be moisture in the soil for proper K uptake by plants. Applying K fertilizer when soil moisture is adequate or before upcoming rainfall will be most effective for ensuring sufficient nutrient uptake, especially if K is applied in-season. The goal here is to maximize the amount of K that is able to be taken up by the plant. If you’re working with soil that doesn’t hold moisture well or are in a drought, consider applying your potassium earlier to your field than normal to allow more time for the nutrient to make its way into the soil solution.
Residue Management
Removing crop residue or stover from your field also removes potassium from your cropping system. Leaving stover in place allows the potassium in plant tissue to return to the soil and become available for future crop use. This will help reduce the depletion of soil K over time.
Sources
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