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Think a year in advance when fertilizing for soybeans

Read Time: 8 minutes

By the Cargill team March 21, 2018

It’s an investment in next year’s crop

We get questions about soybean fertility every year. With all the research showing lack of response to synthetic fertilizers, I don’t have an easy answer.

More and more, we’re looking at how and when we can get nutrients in the soil in advance of soybeans, hoping that by the time they’re seeded, the fertilizer will have become something they can use. So, what can we do for fertility in this crop year to prepare for next season’s soybeans?

Choose the right field for your soybeans

Yes, it’s the old song and dance. You’ve probably heard it multiple times from multiple agronomists. But soil tests before soybeans are even more important than for other crops. If you’re getting ready to put more fertilizer into a field to prepare it for beans, you need to make sure it’s the right field, and soil tests are the best way to inform that decision.

You want to see a pH below 7.3 if it at all possible. However, if you’re in an area like mine, where 7.3 is the low end of the pH scale, carbonates and soluble salts come into play. Soluble salts below 1 mmhos/cm-3 and carbonates below 5% will reduce your risk of iron deficiency chlorosis (IDC). If you want to see that soybean crop reach its full yield potential, you’ll want to keep it free of IDC.

Don’t hold back on P and K

There have been plenty of studies around P and soybeans, and these have shown the ideal soybean field should have P levels higher than 10 ppm. Soybeans love to mine the soil, and keeping those P levels high means there will be nutrient there to be mined.

If you’re going to fertilize for this year and next year’s crop, you must know what nutrients are critical. You also want to be sure that you’ve picked a field that can grow soybeans – because their nutrient requirements are much higher than you might think.

In my territory (the Red River Valley of Manitoba), 50 bushel or higher soybeans are common on a good soybean year. According to IPNI (International Plant Nutrition Institute), a bushel of soybeans takes up 1.1 lb P2O5/bu and 2.3 lb K2O/bu.  This means you’re looking at uptake requirements of 55 lb/ac P and 115 lbs/ac K to reach 50 bushels.

Depending on what your yield goals and rotation are, you could be looking at applying nearly double your usual P and K fertility if you’re looking to fertilize for both crops. 

Make your fertilizer work for you

Every farm is unique, and applying all the fertilizer for two crops at the same time might not be possible. You have to keep in mind how many pounds your equipment can apply per acre, and there are always toxicity concerns if you’re putting down P and K in the seed row. The goal is to fertilize for two successful crops, after all.

What about alternative timing or methods? More and more growers in my area are starting to apply P and K in the fall before their planned soybean crops. If this is an option on your farm, the most effective way to apply is banding, which can prevent runoff losses come spring and snow melt. P is incredibly immobile in the soil, and depending on texture, K doesn’t tend to move a lot either, which means that come spring seeding, the nutrients applied in the fall should be there and ready for your spring seeded soybeans.

What will your upcoming crop yield?

If only we could answer this question right now! Although we can’t definitively predict the future, we can be realistic about expectations. We know from experience that yields on any given year can surprise you. If you spring applied fertilizer for a 50 bu wheat crop and a 40 bu soybean crop, only to get 70 bu wheat in the end… well, there may not be a whole lot left for next year’s soybeans. 

Your local Cargill agronomist is ready to help you figure out the best way to plan for your future (and current) soybean crop.