Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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April 18, 2008

Iowa State University Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246




            The wet weather is slowing down spring field work and has already delayed the planting of wheat and oats. Those planning to try some spring wheat this year may want to change those plans if the rain continues next week. Potential yields decline for both oats and wheat about 10% per week for each week planting is delayed after April 15, and an additional 15% per week if planting is delayed beyond May 1. Lance Gibson has a nice fact sheet on growing spring wheat in Iowa at




               There does not appear to be widespread problems with winter-kill, but some fields in the area do have patches where ice sheets formed and smothered out the alfalfa. The smothered out areas tend to be in low spots where ice accumulated, and are more likely to have occurred in fields where the alfalfa was cut or grazed short in the fall. One option for these fields is to try to extend the stand another year or two by inter-seeding red clover, perennial  ryegrass, or oats into the thin areas. Its best to wait until the alfalfa has about 6 inches of growth to make a final determination on whether the stand is too thin to keep. The stem count method can be used then and is usually more reliable than counting crowns. Optimum yields are obtained with stem counts of 54 or more per square foot (regardless of stand age). Areas with stem counts of less than 40 per square foot (4 crowns per square foot on older stands) usually have enough of a yield loss that they either should be rotated out of alfalfa or inter-seeded to prolong the stand.
               We are approaching the ideal planting window for both corn and soybeans. Although timely planting by the first week of May is important for obtaining optimum yields for both crops, any potential yield gained can be more than lost if the crop is mudded in to try to beat the clock. Small mistakes made at planting time can haunt you the rest of the season. There is little change in yield potential until planting is delayed after May 10, and even with late May plantings, yields usually do not drop by more than about 10%. Many producers can get most of their corn planted in about 3-4 days, so starting a day too soon and planting half the corn under marginal conditions usually doesn’t make sense. Some points to consider with corn planting this spring:
1.   Don’t plant into wet soils. This can lead to sidewall compaction which can lead to season-long problems. The roots will have difficulty growing through the compacted zone made by the planter and will be pancaked into a flat plane in the direction of the planter. This can lead to uneven corn growth, rootless corn, and K deficiency symptoms due to poor root growth. Poor root growth will be an even greater problem later if the summer turns dry, as Elwynn Taylor has been predicting. Mark Hanna advises producers to use “gentle” planter settings this spring if forced to plant under marginal conditions to try to reduce planter-caused soil compaction.
2.   Don’t plant too shallow. When soil moisture is plentiful producers are tempted to plant corn more shallow. For every corn field I see with problems caused by planting too deep, I see a hundred fields with problems caused by planting too shallow. If the seed ends up being less than 1.5 inches deep, problems such as rootless corn and K deficiency symptoms are much more likely to occur. Even if the seed is placed 1.5 inches deep, sometimes the soil can settle after planting or there can be soil erosion so that the plant actually “sees” a more shallow depth. Corn should be planted 1.5-2” deep and error on the deep side. 
3.   Shoot for corn stands of 30,000-34,000 plants per acre. Ideal corn seeding rates have been increasing at the rate of about 400 seeds/A/year. Average corn yields per plant haven’t changed much in the past 50 years. Most of the yield gain has been from breeding corn that can tolerate an increased population. If you are still planting the same population you did 10 years ago, you’re paying 2008 seed prices and only getting 1998 yields. 
4.   Pay attention to details at planting. A little extra time making sure planter settings, seed spacing, depth, and population, and soil conditions are correct can pay big dividends, especially with today’s prices.




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            Certified Crop Advisors can obtain 5 hours of credit (including 2 hours of soil and water) by attending a special session in the morning followed by the afternoon tour at the ISU SE Iowa Research & Demonstration Farm near Crawfordsville on June 26. More details will be posted soon.



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

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Last Update: April 18, 2008
Contact: Jim Fawcett

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