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Frequent information updates for agricultural audiences

Spring Soil Fertility and Fertilizers - from Mike Roegge

Posted by John Fulton -

It's getting crunch time. April 1st is here and past and as I write this the prediction is for rain two of the next 4 days. Many of you have yet to apply dry fertilizer for this years crop, and quite a few corn acres need nitrogen applied as well. The days are going to be long this spring.

Fertilizer prices have really eased since last fall. They're still very high, but at least we've gotten a little break. The question still remains though, how much, if any, fertilizer does this years crop really need? And to answer that question, you'll need a recent soil test. Use that test to determine if your crop will benefit from phosphorus or potassium. Based upon data from IL and IA, soil test phosphorus levels of 20 #/acre will provide 97% of maximum corn yield and 100% of soybean yield. Soil test potassium levels of 250#/acre will provide 94% of corn and 96% of soybean yield.

The question is then what is your current soil test, and if they're lower that these numbers, what will it cost to bring them up. Or if they're higher, how much can you save by not fertilizing. These soil test levels are not all that high. Many fields are probably at or above that level. But if you elect not to fertilize this year, your soil test level will go down as the crop draws up nutrients. Just remember, you can't play this game very long without sacrificing yield, unless you have very high soil test levels.

Nitrogen is the other concern now. With (likely) limited time to perform field work, every minute counts. Do you really want to be pulling a tool bar across the field when you could be planting corn? There are other nitrogen sources available, and this year may be the year to consider them. Liquid UAN (28 or 32%) can be applied with the herbicide. Yes, it can be subject to loss since it's surface applied (unless you incorporate your corn herbicides). However, rainfall within 10-14 days of application will eliminate those loss concerns. There's also a product called Agrotain, that can be used to limit loss as well.

Urea can be applied with the dry fertilizer as another option. Again, the concern is loss. And the concern is greater with urea versus UAN (since only half the nitrogen in UAN is subject to loss whereas all the nitrogen in urea is). We usually recommend that urea be incorporated to reduce opportunities for loss. Or, Agrotain can be used with urea to help reduce loss. Or another alternative would be coated urea, which breaks down via moisture and temperature, taking 4-8 weeks to do so. The only concern with coated urea is that it can float away if surface applied and not incorporated, and heavy rains occur.

Of course, sidedressing is another option. Which is the method that would allow you to reduce your nitrogen rate since you'll be applying closer to the time when the crop would utilize the fertilizer.

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