Don’t Forget About Potassium When Making Fertilizer Plans for 2021
Dry weather conditions early in the 2020 growing season brought about some issues related to potassium (K) that we have not seen for a few years, write Dan Kaiser, Extension nutrient management specialist and Jeff Vetsch, soil scientist, at the University of Minnesota Extension.
Soil moisture is required for plants to access soil potassium. Dry weather conditions and soils where K is stratified near the soil surface can lead to more prevalent K deficiency with plants on marginal K soils.
Potassium fertilizer guidelines for corn and soybean were updated before the 2019 growing season, suggesting higher critical levels for loam and clay loam soils. Suggested K application rates were also adjusted for soybean, particularly for the medium soil test K category (101-150 ppm).
Two research projects are underway to further refine the fertilizer K guidelines for corn.
A study funded by the Agricultural Fertilizer Research and Education Council (AFREC) is trying to determine whether the suggested reduction in the K application rate in the current U of M guidelines is valid. Two trials were established in southern Minnesota at Waseca and near Rochester on field sites where K soil test values varied from Low to Very High. Observations from the two locations showed greater corn growth early in the growing season where the same rate of K was banded compared to broadcast applied. Past research has demonstrated a benefit to banding K in reduced tillage situations as it helps maintain K availability deeper in the soil profile if the upper soil surface is dry. Conventional tillage is used in the current studies.
A study funded by the Minnesota Corn Research & Promotion Council began in 2019 to study the impacts of soil chemistry on potential differences in how corn responds to K. One item of interest for this study how much K was required to maximize grain yield on very sandy soils. Several on-farm trials were established in Minnesota to assess differences in soil chemistry, particularly clay species, across the state. The goal is to study factors such as clay type, cation exchange capacity, and K base saturation and how they relate to corn K response. This study will be continued with additional research sites in 2021.
Continue reading at the University of Minnesota Extension.
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