Iowa had only 18% of its corn planted as of Sunday May 4, thanks to a very soggy April. That compares to 42% a year ago at this time and 64% for the 5-year average. The weekly survey of planting progress and weather conditions was released May 5 by Iowa Ag Statistics Service, the Iowa field office of USDA's National Ag Statistics Service.

The government survey indicates farmers were able to start getting into fields in parts of western Iowa to apply fertilizer and to plant corn this past week. The majority of that 18% of the corn planting that has taken place in Iowa so far has been in western Iowa. Farmers in the central and eastern parts of the state are still facing wet conditions and field work is just getting started there as of May 5.

Some farmers have begun planting corn in certain parts of central and east central Iowa, selecting the higher ground to plant on. They'll have to come back later and plant the lower parts of fields that are too wet now, notes Roger Elmore, Iowa State University Extension corn agronomist.

Northwest Iowa one-third finished

The areas most suitable for planting have been in northwest and western Iowa so far this spring. The survey shows northwest Iowa was able to plant over one-third of its expected 2008 corn acreage last week. West central has 30% and southwest Iowa has planted 20% of its expected corn acreage for 2008.

Is Iowa dramatically behind at this stage of the game in terms of getting a corn crop in the ground for 2008? "No, we are not, if we can get good planting weather this week," says Elmore. "Farmers can put a lot of corn in the ground per day."

"Last year during one week—I think it was this first week of May a year ago—Iowa planted 1.4 million acres of corn per day," he says. "At that rate, Iowa farmers can plant the state's entire corn crop in 10 days. Let's just hope for 10 days of nice weather so we can do that this spring."

Should you apply N or plant corn?

To save precious time, some farmers are going ahead and planting corn and will apply nitrogen later—after they finish planting. "It's good if you are able to get nitrogen fertilizer applied for your corn before you plant," says ISU Extension soil fertility specialist John Sawyer. "Obviously, nitrogen is a very important nutrient for good corn yields. If you can still get the N applied without slowing down your planting progress, go ahead and apply the nitrogen before you plant."

Sawyer prefers to see nitrogen applied before the corn is planted, for several reasons. But you can make sidedressing work too, he adds.

Some farmers are applying dry nitrogen fertilizer, some use liquid and some are applying anhydrous ammonia. "When you look at pricing of products, anhydrous ammonia historically is the least expensive nitrogen source and that continues to be the case today," notes Sawyer. "So a lot of farmers like to use anhydrous."

Anhydrous has special considerations

Anhydrous ammonia must be injected into the soil, while a dry product like urea can be broadcast and incorporated. Liquid N, which is a urea-ammonium nitrate solution, can be broadcast and incorporated into the soil.

A concern with anhydrous is the potential for corn injury. After corn is planted, if the seedling is too close to the ammonia band in the soil, young corn roots can be burned or stunted by the ammonia. "You need to have good soil conditions when ammonia is applied," says Sawyer. "The ammonia needs to be applied deep enough, to minimize the potential for damage. When ammonia is applied before corn planting, you don't want the ammonia injected too shallow because if soils are wet, it puts the ammonia band closer to a future corn seedling."

There is no exact "safe" waiting period before planting, and anhydrous ammonia injury to corn can happen even if planting is delayed for a considerable time period after applying ammonia. "This happens because the risk of ammonia injury depends on many factors, with several that are not controllable," he says.

A couple things farmers can do:

• Wait and apply ammonia when soil conditions are good.
• Apply ammonia at the right injection depth. That is, an injection depth of seven inches or more.
• If you can't control the injection placement relative to future corn rows, apply the anhydrous at an angle across the field.
• After applying the ammonia, wait several days before planting corn.
• If you can control the injection placement with GPS guidance positioning technology, such as swathing or autosteer, then split the future corn rows to inject ammonia. With this system there is no waiting period before you plant corn.

By applying the ammonia at an angle to the rows in the field, the anhydrous knife tracks won't match up with the corn rows when the corn is planted after you apply the anhydrous.

If you are using the new RTK autosteer type of equipment where you know where you are putting the ammonia, then you can split the row middles between the future corn rows and avoid potential damage to the corn plants.

What about sidedressing N?

Sidedressing is an option. This spring, some farmers are switching from preplant application to sidedressing their N. "They can do that--switch from a planned preplant application to a sidedress," says Sawyer. "But they need to work closely with their fertilizer dealer to make sure the type of nitrogen fertilizer product they want to use is available."

Also, make sure you have access to sidedressing equipment. Some of the toolbar applicators can work both preplant and sidedress--and some can't.

What works best for the corn—preplant application or sidedressing of N? If you are committed to getting your corn planted as quickly as you can because you feel it will be difficult to plant it later due to wet weather conditions or perhaps you will be getting past the time when the corn can yield at its highest potential--would you then go in and plant the corn first and follow with the fertilizer?

Sidedressing has benefits, too

Citing the benefits that can come from sidedressing—mainly you are applying the N closer to the time when the corn can use it—Sawyer has no problem with sidedressing. "It's a good practice to sidedress nitrogen for corn," he says. "If someone is doing that and already has a sidredressing plan in place, that's great. If they can switch to that plan and can get anhydrous ammonia and injection equipment or if they can inject liquid UAN sidedress, that is a very good approach and I encourage people to do sidedress."

The downside is not everyone can switch from preplant to sidedress, both because of getting the nitrogen product when they want it--and also having the equipment to make the application. "But from an agronomic view, for supplying nitrogen to a corn plant, sidedressing is a very good approach," says Sawyer.

You need to make sure the corn plant has access to N in its early growth stages. "This would be even more critical for a corn-after-corn crop rotation," he says. "So by having some nitrogen fertilizer applied either preplant or as a 'weed and feed' application, or even better yet--as a starter fertilizer, these options will carry your crop along until the sidedress application is made and then the plant can get access to the nitrogen that is sidedressed."

Sidedressing is a great practice, if farmers can get it accomplished. "Those who sidedress can plant corn and then they need to apply the N before the corn gets too tall," notes Sawyer. "You don't want it to start raining and keep you out of the field so you can't sidedress and then the corn keeps growing and suddenly it's too tall to get the applicator through and you never get the nitrogen applied. However, considering these pros and cons, sidedressing certainly is a viable option to help farmers manage nitrogen fertilizer."