How far ahead in terms of calendar days should you apply anhydrous ammonia before you plant corn in that same field? That's an often-asked question this time of year. Brian Lang, Iowa State University field Extension agronomist at Decorah in northeast Iowa, passes along the following information and guidelines.

University of Illinois conducted research where corn was planted at a depth of 2 inches on a silt loam soil on top of NH3 injection bands. In this study, there were three NH3 injection depths (4, 7, and 10 inches), three dates of planting (0, 1, and 2 weeks after NH3 application), and two nitrogen (N) application rates (100 and 200 lb N/a). There was also a control treatment where no NH3 was applied.

The 100 lb N/a rate showed no reduction in stand compared to the control 27 days after planting for any injection depth or date of planting. The 200 lb N/a rate showed significant stand reduction at a 4-inch NH3 injection depth, but no stand reduction at the deeper depths when planted the day of NH3 injection.

Depth of injection more important than days

Plant height was slightly stunted 41 days after planting when 100 lb N/a was injected the same day as planting at a 4- or 7-inch depth; if injected at 10 inches there was no stunting apparent. While, the 200 lb N/a showed severe, slight, and no stunting for the 4, 7, and 10 inch NH3 injection depths, respectively.

Overall, depth of NH3 injection was more important in reducing injury than was the amount of time between NH3 application and planting.

Follow these guidelines to minimize corn injury

To prevent or minimize injury when planting corn a few hours after NH3 application, Lang advises farmers to:

* Inject NH3 at least 7 inches deep and perhaps as deep as 10 inches if possible.
* Do not plant the corn row directly on top of the injection bands. If possible, apply NH3 at an angle relative to the corn rows.
* Lower N application rates will minimize risk of injury (e.g. typical N rates in corn-soybeans vs. corn-corn situations).
* Ensure that the soil closes behind the knife openings to limit N loss and movement upwards towards the seed.