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Get set for a wet spring

Last fall’s prolonged harvest and wet conditions didn’t leave much time to get fieldwork done, such as tillage and fertilizer application. It’s hard to get a handle on how much work is being pushed into this spring. But from talking to colleagues around the state and to farmers and fertilizer dealers at winter meetings, there will be plenty to do before the corn planters roll.

In Iowa, usually about half of the nitrogen fertilizer applied is anhydrous ammonia, and about half of that is applied in the fall. But in some areas of the state, that job didn’t get done last fall. Also, P and K fertilization was limited, as was soil sampling.

We’ve been cautioning farmers this winter not to make winter applications of fertilizer on bare frozen ground with slopes greater than 4% to 5%, or to ground with deep snow cover, to avoid fertilizer runoff with snowmelt. And here in western Iowa, it’s been a winter with plenty of snow to melt. That means a full tank of soil moisture and a likely later-than-preferred start for fieldwork.

Consider trying no-till

If you’re planting soybeans following corn, you should consider no-till. ISU research across the state for the past seven years with various tillage systems shows no significant difference in soybean yield among all tillage systems. If you are planning on corn following soybeans or corn following corn, tillage recommendations will vary depending on soil type.

The most challenging situations are where tillage is needed to help warm up the soil. Rather than doing tillage, you may consider the attachments on the planter. Some farmers adjust the row cleaners to more aggressively move the residue aside and create a strip to help warm the seedbed and promote early seed germination. While we don’t want to be too aggressive and move soil and create a trench, removing crop residue from the planting zone can be as effective as doing tillage.

Pay attention to soil moisture

Pay attention to soil moisture conditions. Light tillage such as with a field cultivator can be effective. But deep tillage can result in soil compaction, which can damage yield, especially if the soil moisture is close to or at field capacity. No matter how rushed you are, stay off of wet soils. Working ground that’s too wet will create problems the crop has to live with all year.

Planting in wet soils can cause sidewall compaction, a problem we saw last spring. Waiting just a day or two to allow soils to dry a little can help a lot.

What if you didn’t get all of your nitrogen applied last fall? You have two choices: preplant or sidedress. If you want to apply early in the spring and can get into the field, anhydrous ammonia is a good form because it converts to nitrate more slowly and isn’t as apt to be lost from the soil. Or use a slow-release form of N, such as coated urea. In the nitrate form, N is more mobile than when it is in the ammonium form.

Some farmers are thinking of switching to a product like liquid nitrogen or UAN, which is half urea and half ammonium nitrate. Remember, with UAN, whether it’s 28% or 32% N, either knifing it in or incorporating it into the soil with light tillage is very important. Or getting some rain on it, usually a half inch or so will do the trick. Or consider using a urease inhibitor if you are going to surface apply and not incorporate. Urea can volatilize and escape into the air.

For nitrate-containing fertilizer, like UAN or ammonium nitrate, apply as close to planting time as possible. Or inject it into the soil after planting, which is preferable to applying in early spring.

Talk to your fertilizer dealer now, for ideas and help in formulating your plans. There may be some opportunity to switch from the product you normally use. But the fertilizer supply-and-delivery system can’t provide for a lot of product switching on short notice.

McGrath is the partner program manager and Extension agronomist for ISU’s Corn and Soybean Initiative.

For more information

To learn more about the Corn and Soybean Initiative, contact your local ISU Extension office or visit Also, for information about fertilizer application and soil fertility, go to

This article published in the March, 2010 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.