Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


Printer Friendly Version

October 28, 2010




Soil Temperatures


Currently, soil temperatures are in the mid 40’s, and with the forecast of highs in the low to mid 50’s in central Iowa for the next week, soil temperatures may stay below 50 for a while. Nitrogen losses have been substantial the last 3 years and losses are greater when N is applied in the fall. Waiting until the soil temperature is below 50 and falling can reduce losses, but it is hard to predict now what the soil temperatures will be in mid-November. In many years it is mid-late November before soil temperatures remain below 50 in central and southern Iowa. For continuous updates on average 4-inch soil temperatures go to: For more discussion on fall N application see the recent article on the ICM News at







It looks likely that we will see temperatures in the low-mid 20s over much of the area tonight. This qualifies as a “killing frost” for alfalfa.  There is an old, persistent false-hood around that alfalfa becomes toxic following a frost.  Alfalfa does not contain any "toxic" compounds that arise from exposure to frost.  However, alfalfa can cause bloat, and immediately after a frost, alfalfa's bloat potential is higher than normal.  An over-simplified and brief explanation for this is:  Bloat is largely caused by a rapid release of soluble proteins into the rumen.  Alfalfa has considerable amounts of soluble proteins.  As cattle eat alfalfa, their chewing action breaks up plant cells and slowly releases the soluble proteins into the rumen.  If the cattle eat recently frosted alfalfa, they eat already-broken cells from the frost which rapidly releases soluble proteins which increases the chance of bloat.  Once the frosted parts of the plant dry, alfalfa's bloat potential is back to normal.




Prussic acid accumulates in the frosted tissue of sudangrass and sorghum-sudan within a few hours after thawing and wilting.  A "light" frost may damage just the tops of plants.  If this occurs, delay grazing or harvest a few days after frost to allow the prussic acid to dissipate from the plant tops.  Livestock can be returned to frost injured sudangrass (18 inches or taller) and sorghum-sudan (28 inches or taller) after 5 to 7 days.  Once a complete killing frost occurs, which is likely to happen tonight, wait until the frosted tissue is drying out (usually about 10 days) before grazing or harvest.


If haying the forage, the curing process decreases the prussic acid content as much as 75%, which removes the feeding concern.  If green-chopping the forage, chop only as much forage as the cattle will consume in 4 to 5 hours.  Never green-chop the forage and let it sit on the wagon overnight.  If ensiling, harvest at proper moisture for your storage structure to ensure good fermentation.  Good fermentation takes a minimum of 4 weeks.  The fermentation process will reduce the prussic acid content.  Since immature plants can contain higher prussic acid levels, leave this forage ferment for at least 8 weeks before feeding.  Never allow horses to graze sorghums or sudangrass at any time.



The 2010 Iowa State University Corn and Soybean Yield Trial data can be found at  As the raw data is accumulated at each location, it is being posted at this web site in spreadsheet format.  Once harvest is complete, the data will be consolidated and analyzed and those results will also be posted at this web site.





Integrated Crop Management Conference – Ames

December 1 & 2, 2010, Ames


Registration begins at 7:30 am Wednesday, Dec. 1 in the Scheman Building and the program concludes at 4:00 pm Dec. 2.  Conference attendees can choose from 36 workshops that offer the latest information on crop production and protection technology in Iowa and surrounding states.  A popular feature of the conference is the variety of guest speakers on the program.  Iowa State specialists invite colleagues in their field to share their research activities with conference attendees.  This provides an opportunity to hear expertise and opinions from across the region and country at one location.  In recent years the conference has filled to capacity with nearly 1,000 producers and agribusiness people in attendance.  The conference is fortunate to have a loyal following of people that attend each year.  While filling to capacity is a good problem to have, we hate to turn people away and encourage people to register early.  Attendees can obtain CCA credits as well as recertification for Commercial Pesticide Applicators in categories 1A, 1B, 1C, 4 and 10.  Register online ($185 now, $235 after Nov. 19) or find more information at the conference website.   Enrollment is limited and no registrations will be accepted at the door.



Ag Seed, Fertilizer, & Chemical Dealer Update

December 9, 2010, 9:00 a.m. – 3:45 p.m.

Highlander, Iowa City


            Updates on weed, insect, and plant disease management will be provided by Bob Hartzler, Erin Hodgson, and Alison Robertson. In addition, John Sawyer will present “Managing Nitrogen Fertilizer Products and Additives for Enhancing Nitrogen Use.” CCA Credits will be available (3 in PM, 1 in NM, and 0.5 in CM) and Commercial Pesticide Applicators can renew their certification in categories 1A, 1B, 1C, and 10 for the 2010 calendar year. The registration fee is $70 one week prior to the event ($85 at the door). More registration information will be available soon.  See



Crop Advantage Conferences

Burlington – January 7, 2011

Cedar Rapids – January 19, 2011

Waterloo – January 26, 2011

Details will be posted soon at



If you have any questions, please feel free to contact the Iowa State University Extension Office.

maroon ball East Central and Southeast Iowa Crops Home Page maroon ball ISU Extension and Outreach maroon ball ISU maroon ball ISU Extension Agronomy maroon ball ISU Agronomy
maroon ball Calendar maroon ball Search maroon ball Jobs maroon ball Feedback maroon ball Internet Resources maroon ball State Extension Sites in Other States maroon ball Local Extension Offices in Other States maroon ball ISU Extension and Outreach Policies

Last Update: October 10, 2010
Contact: Jim Fawcett

Nondiscrimination Statement and Information Disclosures