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Corn and soybean fertilizer guidelines for Minnesota: Spring 2022 update


Tractor distributing fertilizer

By: Dan Kaiser, Extension nutrient management specialist

Proper nutrient management is a key component of profitable corn and soybean operations. With new data come new fertilizer guidelines for corn and soybean. These guidelines reflect recent research findings from around Minnesota. This blog post highlights the changes and provides links to web pages with the full guidelines for both crops, as well as printable PDFs of both publications.

Corn fertilizer guidelines

With the addition of data from the 2019, 2020, and 2021 growing seasons, we updated the suggested nitrogen rates (Table 1) in the corn fertilizer guidelines. Suggested nitrogen rates for non-irrigated corn grown in the southern two-thirds of Minnesota increased slightly for both corn-following-corn and corn-following-soybean. Current fertilizer prices are hovering at or around the 0.15 price ratio. At that price ratio, the updated suggested rates are similar to those in the previous guidelines when fertilizer prices were around the 0.10 price ratio.

Another change in Table 1 is that the 0.05 and 0.20 price ratios are no longer included. We have very rarely seen fertilizer prices low enough to hit the 0.05 price ratio, and, other than this year, we typically are not close to the 0.20. I added price ratios of 0.075 and 0.125 as we have seen prices around the 0.075 ratio in the past. If you want to see data for different price ratios, the regional corn N rate calculator has been updated and allows you to compare up to four price ratios using current fertilizer and crop prices.

The guidelines for corn grown on sandy soils with or without irrigation have not been updated. We will be compiling the irrigated corn data in 2022.

Research focused on evaluating the potassium (K) guidelines should be wrapped up later this year, so there will likely be another update to the corn fertilizer guidelines before the 2023 growing season. If you want to learn about our ongoing K study, read this recent blog post.
Corn additional resources:

Soybean fertilizer guidelines

Small changes were made to Table 4 of the soybean fertilizer guidelines for phosphorus (P). In the past, no P was suggested for the Medium STP class even though the equations developed for variable rate application suggest applying some P. This was confusing for consultants and growers when coming up with fertilizer management plans. Now, a small amount of P is suggested for the Medium class, such that the equations and table should generally agree.

It is important to remember that the probability of getting a response to P in the Medium class for soybean is relatively low (23% according to Table 3 in the guidelines). If you are applying P, it can still be applied ahead of corn, or, if you are in a high pH situation, application every year is warranted.

We are currently wrapping up a study, funded by Minnesota’s fertilizer tonnage fee through the Agricultural Fertilizer Research and Education Council (AFREC), comparing fall and spring application of P ahead of soybean and will update you on the results at a later date.Soybean additional resources:
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Support for Minnesota Crop News nutrient management blog posts is provided in part by Minnesota's fertilizer tonnage fee through the Agricultural Fertilizer Research & Education Council (AFREC). Learn more at MNsoilfertility.com
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