By Luke Fuhrer and Doug Houser
As harvest is starting to wrap up in Iowa and the cooling temperatures are making their appearance right in time for fall activities, it’s time to think of our next field operation, anhydrous ammonia. Anhydrous ammonia is an effective nitrogen fertilizer for Iowa corn production, but successful application takes more than an open field and available equipment. Soil temperature, soil moisture, placement, and safe handling all determine whether an application protects your fertilizer investment, and the people doing the work.
As fall fieldwork progresses, resist the pressure to apply simply because harvest is finished. Let field conditions guide the decision.
When should fall applications begin?
Iowa State University Extension and Outreach recommends waiting until soil temperatures at a 4-inch depth are below 50°F and continuing to trend lower. Check the predicted forecast as a brief cold spell followed by warmer weather can allow nitrogen conversion to accelerate again. Use the Iowa Environmental Mesonet soil temperature maps as a starting point, then confirm conditions in your fields. Air temperature and the first frost are not substitutes for soil measurements.
Why does temperature matter you may ask? After injection, ammonia reacts with soil moisture to form ammonium, which is held by clay and organic matter. Soil microorganisms gradually convert ammonium to nitrate, a form more vulnerable to loss through leaching or through denitrification in saturated soils (Figure 1). Cooler temperatures though do not completely stop this from occurring but slows that conversion.
Source : iastate.edu