CHAMPAIGN, Ill., 10/7/21: Favorable weather has helped push Illinois’ fall harvest progress well ahead of normal. As a result, producers may be considering early application of fall fertilizer following harvest. University of Illinois experts caution that fall nitrogen fertilizer application on soils warmer than 50 degrees can result in loss of effectiveness and potential environmental issues.
The unusually warm start to fall has caused soil temperatures across the state to remain 5 to 10 degrees warmer than average for this time of year, according to Illinois State Climatologist Trent Ford at the University of Illinois’ Illinois State Water Survey (ISWS).
Measurements at ISWS Water and Atmospheric Resources Monitoring (WARM) Program sites show 4-inch soil temperatures under sod have remained in the high 60s to low 70s across the state. Daily average 4-inch soil temperatures on October 6 ranged from 66 degrees at DeKalb to 74 degrees at Rend Lake.
Given these warm soil temperatures, farmers should seriously consider holding off on fall fertilizer and manure applications for at least two or three weeks, according to Jay Solomon, Illinois Extension educator based in Freeport. Applied nutrient loss and potential environmental impacts are the primary concerns for applications to warm soils.
The Illinois Agronomy Handbook recommends not applying fall fertilizers until the daily maximum bare soil temperature at 4 inches is below 50 degrees. Above this temperature, the rate of nitrifications increases significantly in soils. This chemical change increases the risk of nitrogen losses through gas emissions and leaching with soil water movement before spring crop planting. On average, the last day with maximum 4-inch soil temperatures above 50 degrees is around November 1.
“The push for application may be to empty manure storages,” Solomon said. “However, these warm air and soil temperatures can increase the potential for odor complaints. The nitrogen volatilized off as ammonia gas can be a major component of the odor produced during application. Keeping the nitrogen in other forms longer benefits both the crop and the environment.”
Farmers may be concerned about the potential of less-than-favorable weather for fertilizer application later in the season. Yet forecasts and longer-term outlooks are not showing any signs of the potential for problematic weather in the next few weeks.
“Both long-range forecasts and outlooks are leaning to near to above normal temperatures at least through the last week of October.” Ford said. In addition, forecasts do not show any indication of persistently wet conditions for the second half of October.”
Current soil temperatures across Illinois are available through the State Water Survey’s Water and Atmospheric Resources Monitoring Program: www.isws.illinois.edu/warm/soil/.
-----
Illinois State Water Survey Media Contacts: Trent Ford, 217-333-0729, statecli@isws.illinois.edu; http://stateclimatologist.web.illinois.edu/; news@prairie.illinois.edu
University of Illinois Extension Contact: Stanley Solomon, Jr., Environment and Energy Stewardship Educator, 815-235-4125, jssolomo@illinois.edu