Soybean School: Application method and timing drive potash economics

When it comes to feeding soybeans, investing in potash will give growers the best bang for their fertility buck.

On this episode of the RealAgriculture Soybean School, Ontario Ministry of Agriculture, Food and Rural Affairs Soybean Specialist Horst Bohner looks at potash soil test values to determine how soybeans respond economically to the nutrient.

Bohner says that a typical 50 bu/ac crop removes 70 pounds of actual potassium. Based on his trials, he says growers should plan to apply potassium at about half the rate of crop removal if the soil test is mediocre. “The further you go down the scale, the more you can afford to put on,” he adds. But if you soil test for K is good, growers don’t get any response.

Bohner also looks at application methods, comparing broadcast to in-furrow application. He notes that potash is mined from ancient sea beds with high levels of salt. As a result, potassium chloride can prove toxic when applied in-furrow, close to the seed.

Research has indicted that broadcasting potash at high rates can also prove detrimental to the crop. In Ontario, Bohner says that up to 300 lbs/ac can be broadcast safely ahead of soybean planting. In the video, he looks at a series of trials he conducted in 2022 that support this strategy. “I think we have to really get into some specific dry soil conditions or extremely high rates of potash before we start to run into chloride problems for soybeans,” he says.

When it comes to timing potash applications, Bohner says shallow soybean roots allow for good flexibility when applying nutrients. Both fall and spring applications are effective. Even broadcasting after the plant has emerged can pay on low potash testing ground if timely rains occur after application.

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