Resist temptation is the message being delivered to strip-till farmers across Illinois.
To ensure that strips get tilled before soils freeze, some strip-till farmers are tempted to apply fall anhydrous ammonia before the recommended dates. But Bob Hoeft, University of Illinois Extension soil fertility specialist, warns that nitrogen loss could be significant if anhydrous is applied too early in the fall.
According to Hoeft, there are two key guidelines in timing a fall nitrogen (N) application:
1. Apply N after the soil temperature at 4" is below 50º F. For farmers who use a nitrification inhibitor, the target temperature is below 60º F.
2. Do not apply N before the third week of October, even if soil temperatures drop below 50º F before that time. By applying nitrogen before the third week, you run the risk that soil temperatures will warm back up above 50º F, creating a greater risk for N loss.
These guidelines are set up so farmers have enough time to apply anhydrous before soils freeze, without running the risk of applying N when the soil is too warm, Hoeft says. But because strip-tillers are so dependent on creating strips during the fall, they have an even greater temptation to push up the dates.
Strip-till is an increasingly popular form of conservation tillage, in which producers till narrow, 7"-wide strips in crop residue while applying anhydrous ammonia during the fall. Come spring, producers plant into ridges in the strips, which were created by the anhydrous applicator.
By tilling narrow strips, the seedbeds will be warmer and drier by planting time than they would have been if crop residue had covered the entire field, Hoeft says. And this translates into improved germination and emergence. At the same time, crop residue still remains untouched on 75% of the field, providing an effective cover on the surface to buffer the soil from erosion.
In other words, strip-till combines the seedbed-preparation benefits of conventional tillage with the erosion-control benefits of no-till.
However, because the strips are tilled during anhydrous ammonia application in the fall, this poses a predicament for southern Illinois producers who would like to use the practice, Hoeft says.
South of Highway 16, fall application of anhydrous is not recommended because some soils in the far southern part of the state never freeze, he pointed out. If the soil does not freeze, the nitrification process continues through the winter, converting the ammonium form of nitrogen to the nitrate form. This means greater losses because the nitrate form of N is more susceptible to denitrification and leaching.
In this area of the state, Hoeft says producers should create the strips in the fall and then apply nitrogen between the ridges the following spring, either before or after planting.
For those producers north of highway 16, the key is sticking to the recommended soil temperature and N application dates – something that most strip-tillers observed faithfully last year, Hoeft notes.
"People really conformed to the recommendations last year," he says. "But the temptation to push the envelope is still there."