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3/26/2012 - 4/1/2012

Is Dry Soybean Seed an Issue for 2012?

By Mark Licht and Terry Basol, Field Agronomists and Andy Lenssen, Department of Agronomy

Areas of Iowa and other Corn Belt states were very dry during soybean harvest in 2011. Subsequently much of the soybean harvest occurred at lower than normal grain moisture levels, including soybeans grown for seed. We have heard reports from farmers, Extension and industry personnel that some fields were harvested with seed moisture as low as 7 percent. Handling seed with low moisture must be done very carefully to prevent damage to seed coats. This includes seed movement during harvest, seed cleaning, seed treatment and delivery to planters. 

Careful handling
At this time it is not possible to prevent damage done during harvest, and typically farmers, elevator operators and seed dealers handle seed as carefully as possible to prevent postharvest damage. Careful movement of seed includes avoiding use of steel screw augers, slower than normal flow rates whether with air, conveyer belt or brush augers, and keeping seed drops as short as possible to prevent damaging soybean seed coats. When handling individual bags of soybeans, simply dropping them onto one another off the back of a truck may damage soybean seed coats. This is even more of a concern this spring given the very dry soybean seed from the fall of the 2011 harvest. Seed with damaged coats rarely contribute to stands. 

Farmers should carefully read tags or papers obtained with each seed lot purchased. Information on Certified Seed tags or Quality Assurance papers will include germination percentage. It is important that farmers use the Pure Live Seed percentage when determining the desired seeding rate. But remember, the germination on tags or papers was the germination when the seed left the point of purchase. Soybean seed often is moved at least two times prior to planting, and each movement can result in decreased germination. However, germination percentage does not always tell the entire story on vigor of seed, particularly for soybean seed. 

Seed Germination Tests
The Iowa State University Seed Testing Laboratory offers several tests that can provide additional, useful information for farmers. These include Sand Germination (7-10 days duration), Cold Germination (Iowa Test, 12-14 days duration), and Accelerated Aging (about 10 days duration). Results from these tests can help determine seeding rates required for each specific seed lot, a particularly important consideration for early planting soybean. Additional information on seed testing by the ISU Seed Testing Laboratory is available at:

A quick home test, called Chlorox Soak Test, can provide useful germination determination. Information on the “Chlorox Soak Test” was provided to us by Dr. Brent Turnipseed, Professor and Manager of the South Dakota State University Seed Testing Lab.  Briefly, the test requires:

  • Mix three fluid ounces of chlorox in one gallon of water.
  • Count out one or more 100-seed lots, depending on accuracy desired.
  • Remove all “splits” or obviously broken seed, and place each 100 seeds in a separate tray.
  • Pour a sufficient amount of chlorox-water solution over the seed so all are covered.
  • After 10-15 minutes, pour off the chlorox-water from each tray and spread out the seed on a paper towel so they may be counted.
  • Count the number of swollen seeds in each 100-seed lot. Swollen seed are damaged seed, and likely will not contribute to stands.

Swollen seed typically should not exceed 10 percent, or 10 of the 100 seed in each lot. This test can be used when harvesting seed to confirm combine operation is not damaging seed, or any other time seed are handled at seed plants or farmsteads prior to planting.   

This year it will be extremely important to consider pure live seed and seed germination when determining seeding rates. Keep in mind research studies have documented that about 100,000 soybean plants per acre at harvest will provide optimal yield in most Iowa environments. Planting sufficient seed to obtain a suitable stand is important, but planting excessive amounts of seed reduces profitability of soybean production. Knowing the germination percentage of each seed lot is important in developing the most profitable planting rates by Iowa farmers.


Mark Licht is an ISU Extension field agronomist serving Central Iowa. He can be reached at or 515-382-6551. Terry Basol is an ISU Extension field agronomist serving Northeastern Iowa. He can be reached at or 641-435-4864. Andy Lenssen is the ISU Extension soybean systems agronomist. He can be reached at or 515-294-1060.

Best Corn Planting Dates for Iowa

By Roger Elmore, Department of Agronomy

Optimum Iowa corn planting dates range from mid-April to the end of April in North Central and Northeast Iowa and to the first or second week in May in other parts of Iowa (see Table). If we consider the differences between early-planting and late planting, yields are reduced less early in the planting season than late. That means that planting early during the optimum window is generally a better practice than planting a few days after the optimum window. Yields drop off dramatically in mid-May across Iowa. If possible, plant corn prior to May 15 to avoid this "slippery slope" of rapidly reducing yield potential.

One of my colleagues said, “Planting early insures that you won’t plant late!” But, we’d both add, that doesn’t mean that you won’t replant. Be cautious. If conditions remain unseasonably warm in early April, this would be a good year for date of planting studies…on a small scale.

The best thinking on corn planting dates is the understanding that we should begin to plant if:

  1. Soil conditions are favorable in mid- to late April
  2. AND they are expected remain that way for a week or so, or actually improve.

For example, let’s say it is April 20 and soil temperatures are in the high 40s and rising fast. Soil conditions are excellent and you’ve got everything ready to go: the best hybrids, your planter is fine-tuned to perfection, the tractor fueled and you need to do something – and the five to seven day forecast calls for more of the same. Would you plant corn?  Most of us without hesitation would say yes.

Let’s change one element of that situation: all of the factors just mentioned remain the same but the five to seven day forecast is for cold-wet conditions. In fact it might even snow. Would you plant corn? At this point some of us may get uneasy and shake our heads gently no. Others pound tables and shout, “Of course I’d plant!” And, given their individual situations and aversion or fondness of risk, both may be valid responses. What I know is that yield will likely be compromised in the second situation due to the factors mentioned above.

The situation described is very similar to what we actually experienced the second week of April 2011 and in mid-March 2012. Some planted with varied results in early April 2011, most waited to plant and were pleased they did.

Once we cross the April 11 crop insurance date, if soil temperatures are in the high forties and rising, plant if soil conditions are favorable and conditions are expected remain that way for five to seven days, or improve. 


Table. Recommended planting date windows for Iowa. Based on multiple-location research, Iowa State University.


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.

Influence of Soil Temperature on Corn Germination and Growth

By Roger Elmore, Department of Agronomy

We experienced June-like temperatures in March. Trees budded, spring flowers bloomed and fertilizer rigs crisscrossed fields. Soil temperatures matched what we normally experience in late April and early May, jumping well ahead of previous records.

Because of the unparalleled warm March weather, many wonder about planting corn. Perhaps some did plant. This year’s warm spring temperatures encouraged early development of flowering trees and shrubs, as well as lawns, pastures and early weed-flushes in many fields - But wait until at least the April 11 crop insurance date to plant corn! Data from other scientists and Iowa planting date studies – suggests to plant corn after mid-April when soil temperatures are near 50 degrees Fahrenheit to maximize yield.

Germination process and soil temperature
Seed absorbs about 30 percent of its weight in water; temperature does not affect that process. But temperature does affect growth of both the radicle (first root) and coleoptile (shoot). With soil temperatures below 50 F, seeds readily absorb water but do not initiate root or shoot growth. This opens up opportunities for insects and pathogens to attack seeds resulting in poor emergence especially if poor seedbed conditions are prolonged. Even though soil temperatures are above 50 F at the time I write this, they can quickly plummet with a cold spell. The odds for more cold weather and or snow are still high before mid-April. With that in mind, to minimize risk, begin planting when soils are 50 F or greater or are near 50 F and rising quickly after mid-April.

Problems associated with corn in cold soils
Cool soil temperatures early in the season increase variability in final stands. We want to give every precious seed the chance of survival unless we intend to overplant to compensate for seed viability lost before emergence.

Cool soil conditions early in the season also lead to more unevenness in growth and development from one plant to another. In addition, once the seed begins to germinate, a significant change in soil temperature can cause problems for mesocotyl growth. To maximize yield, manage corn to reduce plant-to-plant variability.

In addition to the effects of early planting on seed development and growth, early planting also exposes seeds and seedlings to increased potential for frost. We know that since a corn seedling’s growing point is below ground until V6 – the sixth leaf stage – it can withstand freezing temperatures when plants have emerged until the V6 stage. Indeed that fact has saved a lot of replanting and the associated costs over the years. 

What we don’t always say – or for that matter understand – is that frost often affects individual plants differently resulting in more variability from one plant to another. That variability can result in unequal interplant competition and lower yield potential. Depending on the potential date of replant though, keeping the surviving stand – albeit of variable plant heights and development – may still be the best option. (See: Replanting Information

In addition to the impact on seedlings, extreme cold snaps can refreeze soils down to seeding depths. This can and does kill seeds and growing points, reducing stands and forcing a complete replant.


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.

'Early' Early-spring Weed Management

by Bob Hartzler and Mike Owen, Department of Agronomy

The unusually warm weather may create additional weed challenges this spring. Winter annuals in no-till fields will likely accumulate much more biomass prior to planting than normal and therefore use more soil moisture, tie up more nutrients and potentially interfere with planting and crop establishment. In addition, weeds such as horseweed (marestail) will grow more rapidly and reach growth stages that are difficult to control much sooner than in a “normal” spring.

Due to these potential problems, applications of burndown herbicides in early April may be beneficial and improve the control of winter annual and early spring annual weeds. An additional benefit of earlier application dates for the burndown is minimizing the risk of including 2,4-D at the higher rates (i.e. 2 pts/A of LV-4) in the program. Of course, there is the important assumption that planting dates are not moved proportionally earlier.

Many farmers will want to include preemergence herbicides with these early spring burndown treatments. While this may provide a clean seedbed at planting and crop emergence, the longevity of weed control is likely to be shortened significantly. The magnitude of this reduction will depend on the time period and weather encountered between application and planting, and the herbicide rate. The rates of many preemergence products have been reduced due to the reliance on postemergence products, primarily glyphosate. If applications are going to be made a few weeks earlier than normal, carefully evaluate the product rates in order to maximize the contribution of the preemergence herbicide(s) to residual weed control after crop emergence.

Preemergence herbicides are a key component of herbicide resistance management. But to be effective, they need to be used in a manner that results in significant control of the target species. Very early applications of preemergence herbicides or reduced rates will greatly reduce their effectiveness on late-emerging weeds such as waterhemp, or large-seeded species such as giant ragweed. Many products specify split applications where a portion of the product is applied early and a remainder is applied at, or shortly after planting. This approach could be beneficial this year where an extended period of weed control may be needed due to early applications resulting from prevailing weather conditions.

Winter annuals are likely to be a greater problem in no-till fields this spring.


Bob Hartzler and Micheal Owen are professors of agronomy and weed science extension specialists with responsibilities in weed management and herbicide use.

This article was published originally on 4/2/2012 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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