Researchers recommend that soil temperatures at the 4-inch depth are 50° F and cooling before applying fall anhydrous ammonia or manure with a high ammonium nitrogen (N) content, such as with liquid swine manure.
Looking at the current 4-inch soil temperatures across the state, we did drop below that 50° F mark this weekend.
However, the weather forecast is calling for warmer temperatures this upcoming weekend, which may result in soil temperatures warming back up into the low to mid-50s again before dropping below 50° F again. You can monitor the 3-day history average soil temperatures in every Iowa county and forecasted 4-inch soil temperatures here on the ISU Environmental Mesonet website.
Historically, the soil temperatures at the 4-inch depth cool below 50° F in the northern third of the state the first week of November. For central and southern Iowa, soil temperatures cool below 50° F during the second week and third weeks of November, respectively.