Blog > June 2020 > Making Potassium Fertilizer Recommendations

Making Potassium Fertilizer Recommendations

June 1, 2020

6.1.20 | Potassium Recommendations v1 from Central Valley Ag on Vimeo.

Tim Mundorf, CVA Nutrient Management Lead
Today we wrap up the Agronomy Focus series on Building a Fertility Plan for N, S, P, & K. Today, we want to focus on potassium. Like phosphorus, potassium is a nutrient we build a long term plan around. We focus on the soil test levels and use crop removal replacement to keep soil test levels in a good range. Usually, that range will be around 200 ppm K in the soil test. Sandier soils sometimes are a little under that number, and heavier soils are often over it, and we will usually make some adjustments based on soil texture. When we think about crop removal, a good rule of thumb is 200 bu corn is going to remove about 60 lbs of K2O while 60 bu soybeans will remove around 85 lbs of K2O.   

Potassium throws a little bit of a curve at us compared to phosphorus. If we look back at those crop uptake curves for the different nutrients, we see that the potassium uptake curve looks very similar to the one for nitrogen. It is much steeper than the uptake curve for phosphorus. We almost never talk about in-season application of phosphorus, but more and more about in-season of potassium. When I think about in-season application in corn, my mind first goes to nitrogen, then to sulfur, and then to potassium. To hit the uptake needed for late vegetative growth, it can make sense to supplement a little in-season K.

Most potassium recommendations focus on potassium chloride, often referred to as potash or 0-0-60. It is by far the most used K fertilizer product and really the most bang for the buck in terms of replacing crop removal or building soil test levels. One hundred pounds of 0-0-60 perfectly matches crop removal for 200 bu corn so is just a natural recommendation that comes to mind.

When we think about in-season application of K, we have some options. Potash (0-0-60) can be applied as a topdress, but I prefer a product called K-Mag. It is a naturally mined blend of potassium, magnesium, and sulfate. It will provide both potassium and sulfur and can be blended into a urea application to give N, K, and S all to the growing crop just prior to rapid uptake. If a grower wants to inject fertility into his pivot, we can accomplish the same thing with Potassium Thiosul (KTS).  

Like we have talked about in previous installments. The best way to purchase fertilizer is to make it part of an overall fertility program developed between a grower and their trusted advisor. If these articles have piqued your interest, set up a time to meet with your Field Sales Agronomist. Work on a plan for soil testing, yield goals, and an overall fertility plan for each of your fields.   

Listen to Tim on the SOIL TALK Podcast today

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