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The NDSU Extension weekly podcast In the Pod: Soybean Updates delivers timely insights and expert advice on soybean production.
You're listening to In The Pod, Soybean Updates, a weekly trek into the latest soybean information from NDSU Extension. When it comes to soil fertility, the three big nutrients are nitrogen, phosphorus, and potassium. Today, we're discussing how potassium can be critical to a soybean crop. Brady Goettl, NDSU's soil science specialist, has the facts. Brady, how important is potassium to soybeans?
Brady Goettl:When we start thinking about our three main macronutrients as it relates to soil fertility, p and k are the two most important in soybeans. We know that we're not having to fertilize soybeans with nitrogen if we have good nodulation, but when it comes down to thinking about potassium, we remove a lot of potassium with a soybean crop in North Dakota, about 60 pounds per acre, which is different than our historical wheat based rotations. So potassium is becoming more and more important because we need to replace what we're removing with those soybean crops. And through long term not replacing that potassium, we're seeing a downturn in soil test values, which is starting to lead to visual potassium deficiencies in soybeans.
Bruce Sundeen:Why is potassium important to soybeans?
Brady Goettl:Potassium plays a strong role in seed quality. What are we harvesting from soybeans? The seed. We need that potassium in order to facilitate the management and the uptake and the metabolism of other nutrients. K helps facilitate all of those things. And if we start having a deficiency in K, it's gonna decrease the overall yield of the plant and how well it's able to take up and process those other nutrients.
Bruce Sundeen:How does soybean farmers achieve higher potassium levels in their fields?
Brady Goettl:Really, it comes down to just applying more k based fertilizers. Historically, our wheat rotations in North Dakota really didn't remove a lot of k from our soils, but now with soybeans and the high rate of removal, we're seeing that downturn in soil test levels. I sampled fields this year that have k levels anywhere from 100 to a 120 parts per million. Our critical level or the point where we won't see any deficiency symptoms or downturn in yield, is somewhere from 150 to 200. So we're much below that critical level.
Bruce Sundeen:When and how do producers identify potassium deficiency?
Brady Goettl:In most crops, we're gonna see a potassium deficiency occurring early in the season. It's gonna occur on the older leaves because potassium is what you call a mobile nutrient within the plant. It's able to take it from the older leaves of the plant and move it to the new growth. So typically, you'd see it in those older leaves. In years like this, we have a unique thing that's called late season potassium deficiency, where actually during pod fill, during dry conditions in fields that are low in soil test K, we'll actually start seeing those symptoms occur on the upper leaves. And that's because all of the K is trying to go towards that seed to produce that yield, and now it's being stripped away from those leaves in the upper part of the plant. What's nice about identifying a potassium deficiency is it's a very obvious, what we call haloing effect around the leaves. You'll have an overall healthy plant, but at early onset of that deficiency, you'll see a chlorosis or a necrosis, so a yellowing to starting to die along that leaf margin, a halo around that leaf that'll slowly work its way to the center. And when you start seeing that, that also means we're losing yield.
Bruce Sundeen:What's the easiest way to keep track of potassium in the soil?
Brady Goettl:Yeah, so the easiest thing is going to be soil sampling, but also thinking about when's the last time we put on potassium fertilizer? How critical is it to my rotation? Am I growing high k removal crops? Corn and soybeans remove a lot of k from our soil. So if we're in a corn and soybean rotation and we haven't put on potash or k fertilizer recently, there's probably a good sign that those soil test levels might be getting low.
Bruce Sundeen:Thanks, Brady. Our guest has been Brady Goettl, NDSU soil science specialist. You're listening to In The Pod, Soybean Updates, a weekly trek into the latest soybean information from NDSU Extension, supported by the North Dakota Soybean Council.