Extension News

Remember 50 Degrees F

Note to media editors:

ISU Extension has established a special Web page to offer farmers risk and energy management tools to help them make better decisions this harvest season. That page is www.extension.iastate.edu/agenergy.



AMES, Iowa --  As the crop continues to be harvested across the states, some farmers are already starting to prepare for next year’s crop. Part of that process crop may include consideration for application of anhydrous ammonia fertilizer.


“I want to remind producers that they need to wait until the soil temperature has cooled to 50 degrees and is continuing to cool before applying this fertilizer,” said John Sawyer, Iowa State University (ISU) Extension soil fertility specialist.


Sawyer says that when anhydrous ammonia is applied to soils warmer than 50 degrees, a chemical process can quickly convert it into nitrate. The nitrate can then be leached from the soil, resulting in the movement from a producer’s field into water resources, or it can be lost as nitrogen gas if soils become water-saturated.


“Waiting for cold soils does not guarantee that fall-applied N will be a successful application practice,” said Sawyer. “Warm fall conditions might occur, or warm and wet conditions may occur the next spring and early summer. However, if one decides to make applications in the fall, then waiting until soils are cold is better than applying early.” The same goes for inclusion of a nitrification inhibitor.  It will work better after soils have cooled.


Soil temperatures can be found at several Web sites. One that shows the three-day, 4-inch depth soil temperature estimates for each Iowa county is Soil Temperatures for Agriculture (http://extension.agron.iastate.edu/NPKnowledge/). The site also can be accessed through the Agronomy Extension Soil Fertility Web site (http://extension.agron.iastate.edu/soilfertility/), either from the weather page or nitrogen topic page.


You can access the average daily soil temperatures from yesterday, two days ago, and three days ago, and you can get the six- to ten-day weather forecast. Four-inch soil temperatures for the previous day recorded at specific sites in Iowa can be found at the Iowa Environmental Mesonet Web site (http://mesonet.agron.iastate.edu/agclimate/display.php?src=/agclimate/daily_pics/4in-temp-out.png).


“The 4-inch soil temperatures are estimated for each county based on interpolation of observed soil temperatures at 14 locations,” said Elwynn Taylor, ISU Extension climatologist . “The estimates are for soil temperatures on level, bare soils. The reliability of the estimates is within 3 degrees F with normal conditions in Iowa. The variation in soil temperature within a locality is generally more than 8 degrees F depending on the slope of the land and condition of the soil. Also listed are dates during the past five years when soils cooled to below 50 degrees F.”


During the past five years the dates when soils cooled below 50 degrees F varied considerably, from late October to late November. “Don't get fooled by a temporary cold spell, especially if it occurs early in the fall. Also watch the six- to ten-day weather forecast, noting that a forecast for 'above' average temperature may signal soil warming,” said Taylor.


ISU Extension offers a number of resources for producers wanting to know more about this soil fertility process.


Integrated Crop Management Newsletter







PM 1584         Cornstalk Testing to Evaluate Nitrogen Management

PM 1688         A General Guide for Crop Nutrient and Limestone Recommendations in Iowa

PM 1714         Nitrogen Fertilizer Recommendations for Corn in Iowa (Web only)

PM 1811         Managing Manure Nutrients for Crop Production


These publications are available through any ISU Extension county office, on the Web at  (/store/) or by calling (515) 294-5427.



Contacts :

John Sawyer, Agronomy, (515) 294-7078, jsawyer@iastate.edu

Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu