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4/5/2010 - 4/11/2010

Updated Planting Date Recommendations for Iowa

Lori Abendroth and Roger Elmore, Department of Agronomy

Note: A full-length summary and publication on this data set will be available later this year. The statistical analysis and recommendations used and stated in this article may be changed slightly given further interpretation. The recommendations are not expected to be altered significantly though and are stated now to aid producers and agronomists this planting season.

Our research group has been working to update corn planting date recommendations based on new field data (2006-2009). As corn growers and agronomists know, corn planting dates have increasingly become earlier over the years. This change is largely due to advancements in equipment, seed treatments, hybrid stress tolerance, tile drainage and reduced tillage. Combine these factors with a desire to maximize the length of the growing season and it is clear why we encourage earlier planting than before.

Our new recommendations are based on multi-year (2006, 2007 and 2009) and multi-location (seven research sites) data for a total of 21 site-years. Plots were planted on April 1, or as soon as possible, and the last planting date was June 1. Once all the data was pooled and analyzed, three distinctive patterns or "regions" emerged for Iowa.

corn planting dates

Recommendations are developed based on achieving a percentage of the maximum yield possible in relation to planting date. Each region had a different response curve, or optimum window of time. These "windows" were developed for each region by identifying the date that optimized yield on average and then expanding the window from there. Recommendations are given for achieving 95+ percent or 98+ percent maximum yield. The window of time that producers can expect to reach 98 percent to 100 percent yield potential in relation to planting date is narrower than the 95 percent to 100 percent window.

Northeast region (red):
This has the narrowest planting window due to the need to maximize the length of the available growing season. Grain yields begin to drop off more significantly here than the rest of the state if plantings are too late. We recommend planting between April 12 and May 2 (95-100 percent yield window) or between April 12 and 30 (98-100 percent yield window). The dataset is limited for plantings before April 12 in this region, which limits our ability to make recommendations prior to this date.

Northwest and central region (yellow):
This has a flatter yield response to planting date than the other regions. In other words, planting date does not appear as important of a management practice here as in other parts of the state. We recommend planting between April 15 and May 18 (95-100 percent yield window) or between April 15 and May 9 (98-100 percent yield window). The dataset is limited for plantings before April 15 in this region, which limits our ability to make recommendations prior to this date.

Southern region (blue):
The yield response in this part of the state is presumably related more closely to rainfall patterns and soil moisture than the length of the growing season since this typically is not a limitation as it is in the northern part of the state. We recommend planting between April 11 and May 13 (95-100 percent yield window) or between April 17 and May 8 (98-100 percent yield window).

Although planting date impacts yield and is an important factor, it is clear that an approximate three- to four- week window exists for growers in each Iowa region to plant their crop and realize 95 percent or greater yield. In terms of planting date, growers should feel secure when planting within the windows cited above. It is interesting to note that the start date for all regions is approximately the same, approximately April 10-15. The difference among the recommendations primarily lies with the length of time each region has from that starting point and the yield reduction that occurs after the recommended window ends.

Thank you to the following ISU faculty and staff for their significant contributions to this project: Stephanie Marlay, Anthony Myers, Robert Foster, Dr. Philip Dixon, Jeff Butler, Mike Fiscus, David Haden, Ken Pecinovsky, Nick Piekema, David Rueber, Ryan Rusk, Jim Secor, and Kevin Van Dee.

More information
An expanded article, with more detail specifically on the methods behind this project and the development of recommendations can be found on the ISU Corn Production website.


Lori Abendroth is an agronomy specialist with research and extension responsibilities in corn production. Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. Abendroth can be contacted by email at or (515) 294-5692; Elmore can be contacted by email at or (515) 294-6655.

Remember to Check Planter Settings

By Mark Hanna, Department of Agricultural and Biosystems Engineering and Roger Elmore, Department of Agronomy

There are several planter settings that must be checked when heading out to the field this spring. Your planter may have been perfectly adjusted for the last field planted in 2009, but likely is not well-adjusted to plant your first field this spring. Soil moisture in the top couple of inches can vary from saturated to moist or even dry depending on sun and wind. For those fortunate enough to be using a new planter, avoid assuming all adjustments are ‘correct’ because it just came from the dealer. Features such as adjustable closing wheel down pressure are on the planter so that the operator can make final adjustments subject to field conditions. 

Planting depth
Planting depths of about 2 inches are appropriate for corn in Iowa. Given this, Iowa State University research shows that corn emerges and produces well from both much deeper and shallower planting depths - provided ideal conditions occur following planting. We can’t count on ideal conditions!

Corn plant crowns and the primary nodal root system form from 1 to 1½ inches below the surface provided soil conditions are good and seeding depth is below that point. Shallow seeding can result in rootless corn and may seriously impact crop standability and yields. Planting too deep can reduce stands and uniformity of stands. In some cases, inadequate planter adjustments coupled with fast planter speeds results in seeding depth variability within a row. Variable seeding depth translates into variable emergence rates which results in reduced yields.

Remember that the planter row unit must carry enough weight so that the depth-gauge wheels are firmly on the soil surface. Otherwise the double-disc seed opener is holding the row-unit out of the ground and seed will be planted too shallow. 

Closing wheel pressure
Virtually all planters feature adjustable down pressure by using a spring on the closing system.  Most Deere, Kinze and White planters use a multi-position lever to adjust surface pressure exerted by two closing wheels. Case planters have an adjustment of spring pressure on two closing discs ahead of a single press wheel. 

Research shows that increasing down spring pressure can increase soil strength and help bring capillary water to the seed if soil is dry. Higher contact pressure may be useful in dry soil conditions. Light or ‘no’ down spring pressure should be used in moist or wet soils to avoid over compaction of soil around the seed. Using no spring pressure, sometimes called the ‘float’ position, supplies the lightest pressure using only the weight of the wheels. In wet soil conditions, consider using a drag chain or tine to close the seed furrow instead of resorting to high spring down pressure that can compact soil. Although rubber-coated aluminum closing wheels are commonly used, some planter operators prefer ‘finger-‘ or ‘spade-type’ closing wheels in wetter soil conditions. 

Depth-gauge wheel pressure
Depth-gauge wheels on either side of the double-disc seed opener need to have enough contact pressure in order to be firmly on the soil surface (to gauge seed depth), but not so much contact pressure that the depth wheels overly compact soil adjacent to the seed zone. In practical terms, this means that when soil moisture is overly moist or wet, use only enough down spring pressure on parallel links attaching the row unit to the toolbar frame to maintain firm contact of the wheels on the soil surface. Some newer planters adjust depth-gauge wheel contact pressure with pneumatic diaphragms. If significant weight has been transferred by down pressure springs for drier soil and you have been rained out of the field, remember to lighten spring tension when going back in to wetter soil. 

For further information see Don't Use More Pressure than Needed on Wet Soils.



Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at or (515) 294-0468. Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or (515) 294-6655.

Leveling Soil for Planter Operation

By Mark Hanna, Department Agricultural and Biosystems Engineering ; and Mahdi Al-Kaisi, Department of Agronomy 

Last fall wet soil conditions during harvest time created unavoidable soil destruction and significant soil scars or ruts. Most likely significant soil compaction took place as the ruts were made. The wheel ruts remaining from harvest and general irregularities after primary fall tillage often lead growers to consider spring tillage to level the soil for subsequent planting operations. 

Although many fields have a chance to drain between rainfall events, soil below a couple of inches of the surface still remains at field capacity moisture content and may be too wet and plastic to respond well to tillage. Soil at field capacity water content is in ideal condition for maximum soil compaction. Therefore if you are planning to work these soil ruts out, check your soil moisture condition before conducting any tillage operation and avoid worsening the problem by increasing soil compaction.

If you determine the soil is dry enough to work, closely check the rut conditions and how deep these cuts are in the soil surface to decide proper management.
• Unless surface irregularities are deeper than planting depth (e.g., 1.5 to 2 inches), tillage is likely not needed ahead of the planter to maintain seed depth.
• If deeper surface irregularities are present, consider shallow tillage with a field cultivator or light tandem disk in those areas to level soil for planter operation. 
• Tilling soil only surface soil avoids pushing, smearing, and compacting wetter soil below the surface. 

For further information on handling ruts left from fall harvest see Soil Management of Harvest Ruts.


Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at or (515) 294-0468. Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or (515) 294-8304.

Compliance or Complacency: Corn Producers and Bt Refuge

By Roger Elmore, Department of Agronomy; Aaron Gassmann and Erin Hodgson, Department of Entomology

Tragic events or situations result in great loss and misfortune. The Tragedy of the Commons - by British writer, William Forster Lloyd, 1832, and cited later by Garrett Hardin, Science 1968 – illustrates this well. Lloyd asked, “Why are cattle on a common (publically-owned pasture) so puny and stunted? Why is the common so bare-worn, and cropped so differently from the adjoining (privately-owned) enclosures?”

Lloyd concluded that individual herdsmen guided by self-interest and personal gain, added more animals to their herds. Other herdsmen did the same, ultimately, ruining the common property. Hardin summarized this by writing, “Ruin is the destination toward which all men rush, each pursuing his own interest in a society that believes in the freedom of the commons. Freedom in a commons brings ruin to all.”

A potential tragedy looms for U.S. corn producers: the loss or reduced efficiency of an important technology, Bt. According to USDA-NASS data, 71 percent of Iowa’s corn acres contain at least one Bt trait compared to 63 percent nationwide – see page 24 in the USDA report. Hybrids with stacked traits occupied 57 percent of Iowa’s corn acreage compared to 46 percent nationwide. This means hybrids on 9.7 million of Iowa’s 13.7 million acres carried at least one Bt trait (see figure)!

While Bt traits protect yield they impose intense pressure on the target pest populations to develop resistance. Many scientists agree that refuges delay or prevent pests from developing Bt resistance.

A grave assessment of compliance
A Center for Science in the Public Interest (CSPI) report released last November summarized producer compliance for planting of refuges. Data were based on industry reports submitted to the Environmental Protection Agency. For Bt corn targeting European Corn Borer (ECB), compliance with refuge size requirements was greater than 90 percent from 2003 to 2005. A trend of decreasing compliance has since occurred, with compliance falling to 78 percent in 2008. Refuge distance compliance figures were slightly better with 88 percent compliance in both 2007 and 2008, but these were down from the 93 to 96 percent compliance from 2003 to 2006.

Compliance and trends for corn rootworm (RW) are more discouraging. Refuge size requirements for RW went from 89 percent in 2006 to 74 percent in 2008. Corn rootworm refuge distance compliance percentages fell from 82 percent to 63 percent in the same three years.

Stacked hybrid refuge compliance and trends were even more discouraging. Size compliance dropped from 78 percent in 2006 to 70 and 72 percent in 2007 and 2008. Compliance to the distance requirement fell from 92 percent in 2006 to 66 percent in both 2007 and 2008.

The CSPI used these data to estimate total compliance over all three categories ECB, RW, and stacked hybrids. The results averaged 73 percent compliance for distance and 74 percent for size. One out of four producers did not comply with the refuge requirements! According to the CSPI report, this amounts to 13.2 million acres in the U.S. that are not in compliance – that’s an area the size of Iowa’s corn crop. On the other hand three out of four producers do comply.

Transgenic hybrid adoption in Iowa, 2000-2009. Data adapted from USDA-NASS.

Why does refuge compliance matter?
Refuges delay pest resistance to Bt corn because susceptible pests emerging from the refuge mate with resistant pests from the Bt field. This dilutes the resistance genes and maintains susceptibility of pest populations to Bt corn. If refuges are too small or too far from Bt fields, a shortage of refuge insects to mate with insects from Bt fields will occur. When this happens, pests will quickly develop Bt resistance.

What’s at stake?
At least three issues come to mind:
• First, if compliance rates do not quickly improve, expect more demands for compliance, insistence to change the regulatory process, and/or steep penalties for noncompliance from groups like CSPI…and rightly so. Based on the CSPI report, 90 percent or greater compliance appears necessary.
• Second, refuge requirements form an integral part of insect resistance management programs. If some producers continue to ignore these requirements, insects may develop resistance to Bt corn sooner.
• Third, every business enterprise – including corn production – bears a social role and responsibility. Peter Drucker, a renowned writer and management consultant, warned that an enterprise, “…that fails to ‘think through its impacts and its responsibilities’ exposes itself to justified attack from social forces. Consumerism and environmentalism, he taught are not enemies to be vanquished, but symptoms of business’ failure to understand its broad social role.” (from Michael Hiltzik, Los Angeles Times, 31 Dec 2009). Some of us ignore our social role!

On the positive side, groups like the National Corn Growers Association place first priority on grower refuge compliance education programs. Certainly with the 2010 introduction of new combinations of transgenic traits, some refuge requirements indeed will change. However, producers planting current ECB, RW, and stacked hybrids must continue to follow the refuge requirements specific for those technologies. We thank the 3 of 4 who comply with refuge requirements.
Insects do not know property lines; our corn fields are the ‘commons.’ Consider the environment, consumers, your neighbors, your kids – or whoever farms after your time – when you decide whether to comply with scientifically-sound, government-mandated, socially-responsible, refuge requirements. Let’s do what we can to preserve this excellent technology!




This article first appeared in Wallace’s Farmer, February 2010.  Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or (515) 294-6655. Aaron Gassmann is an assistant professor of entomology. He can be reached at or (515) 294-7623. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at or phone (515) 294-2847.

Maintaining Stored Grain Topic of April 9 Webinar

By Charles Hurburgh, Department of Agricultural and Biosystems Engineering

A webinar scheduled for 11 a.m. April 9 will give farmers and grain elevator operators information on keeping their stored grain in good condition.

Last fall’s wet conditions meant that many producers had to harvest corn and soybeans before it had a chance to dry to optimal levels. As a result the condition of grain stored in Iowa is at risk because of mold and insect problems.

The trade publication Grain Journal is presenting the webinar at no cost. Charles Hurburgh, Iowa State University, and Dirk Maier, chairman of the Department of Grain Science and Industry at Kansas State University, will offer ways farmers and elevators can ensure the quality of their stored grain.

The hour long webinar will cover:
• The current grain management and quality situation at Midwest grain elevators
• Grain quality practices that can minimize damage and subsequent quality management problems
• How to condition high-moisture grain to prevent further damage, maintain quality in storage and maximize safety by preventing dryer fires

Register for the webinar online at: High speed internet service is required for the webinar.


Charles Hurburgh is an agricultural and biosystems engineering professor who manages the Grain Quality Research Laboratory and the extension-based Iowa Grain Quality Initiative. He can be contacted at (515) 294-8629 or by email at

This article was published originally on 4/12/2010 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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