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4/25/2011 - 5/1/2011

Early Preplant Time – Opportunity Lost!

By Micheal Owen, Department of Agronomy

Weeds are well underway for another year of reduced crop yields. Except for those producers that were able to take advantage of the one or two days available for field work in April, the opportunity to use a soil-applied residual herbicide for weed management in corn —in the manner that provides the most stewardship and economic benefits —has been lost. Now is the time to consider the next best opportunity to protect crop yields, as well as provide stewardship to mitigate the evolution of herbicide resistance in weeds for fields to be planted to corn. 

In no-till fields, DO NOT wait to apply the traditional burndown herbicide treatment until after the corn has emerged. The philosophy of the delayed burndown approach is to reduce trips across the field; however, this approach usually guarantees considerable loss of crop yield potential and thus profit. Given the corn market now, this could be costly indeed. The best option now is to apply residual herbicides in combination with a burndown product immediately prior to, or immediately following planting, but prior to the emergence of the crop.

Early preplant herbicide opportunities still exist for soybeans, but given the weed growth that currently exists, a burndown product should be included with the soil-applied residual herbicide. The sooner a soybean herbicide is applied, the better the weed management and the greater the soybean profits.

Selection of herbicides must be done with an understanding of existing resistances to herbicides in weeds. Consider that all waterhemp in Iowa should be considered resistant to ALS inhibitors (Group 2) herbicides. Thus, any herbicide (single product or pre-package mixture) that is a Group 2 product will not provide any control or stewardship with regard to waterhemp. In Iowa, resistance to ALS, HPPD, triazine, PPO and glyphosate products exists in waterhemp populations and in most instances, the waterhemp populations have multiple herbicide resistances. The take-home message is make herbicide selection a well-thought and informed decision.


Micheal Owen is a professor of agronomy and weed science extension specialist with responsibilities in weed management and herbicide use. Owen can be reached by email at or by phone at (515) 294-5936.

How Much Corn Can We Plant on a Good Day in Iowa?

By Roger Elmore, Department of Agronomy

Corn planters are rolling in parts of Iowa. This is good news; the bad news is that only 3 percent of our crop was planted as of April 24. On Monday, April 25, Iowa Secretary of Agriculture Bill Northey commented on the current NASS Iowa Crops and Weather Report and the slow corn planting progress to date. There was only a half-day suitable for fieldwork the previous week so little corn planting progress had been made. 

As I write this on Friday, April 29, although planting has started again in some places, rain is forecast for tonight and tomorrow for parts of Iowa. Secretary Northey on Monday also presented useful historical crop planting information indicating that we can plant up to slightly more than 20 percent of our corn acres in one week,  based on the five-year average. Remember though, the five year average includes one of the fastest planting seasons on record, 2010, and one of the slowest, 2008.

Another way to look at this is to consider how many acres are planted per day suitable for fieldwork. On average, during any week this time of year, fields are suitable for work about 3 ½ days, or half the time.

We can put a lot of corn in the ground quickly! Last year, based on data from the Iowa Crops and Weather Reports, Iowan’s planted from 37,000 acres per suitable day to nearly 1.4 million acres (see Table). In 2008 and 2009, over 1.2 million acres were planted per day suitable for field work during the best weeks.

Several factors contribute to our ability to plant rapidly. Modern planters are larger than older models, fields are larger, more fields have improved drainage with tiles, and global positioning systems, improved operating lights, planter monitors and well-equipped tractor cabs all allow farmers to plant longer hours with less fatigue. In addition, the common knowledge that yield penalties generally are less with early planting than late planting has spurred this trend.

It remains to be seen how long it will take to plant our estimated 13.9 million acres this year. Iowa farmers are well-equipped to do it in record time, if the weather cooperates. We just need ten excellent days!

Table.  Iowa corn acres planted per day (that farmers could be in the field), 2008, 2009, and 2010. Data adapted from USDA-NASS.


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.

Maximizing Yield Potential by Optimizing Soil Management Practices

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

Current weather conditions and wet soils cause certain anxiety and concerns for late planting, especially for corn. Spring weather this year definitely creates challenges in preparing fields and getting certain field operations done on time, such as tillage, anhydrous injection, manure application, etc. Decisions to conduct these operations need to be made carefully regarding the soil moisture conditions. The current soil moisture status makes the soil conditions susceptible to soil compaction, low soil temperature and soil erosion just to name a few. These problems can be yield robbers. Let’s discuss them individually and why we need to be more patient in entering fields and why waiting a few days may pay off significantly.

Soil Compaction and yield

Soil compaction can occur when soil moisture is at field capacity, where the soil retains the maximum amount of water as dictated by soil texture and natural drainage of that particular soil.  The best way to determine if your soil is at field capacity is to check your tile drain. If it is still running your soil is saturated and you need to consider waiting before entering the field. 

However, once the tile stops running then the soil is at field capacity. As a rule of thumb when soil is at field capacity, it is advisable to wait one to two days before entering the field, because at such conditions soil compaction and side wall compaction (when soil smeared by anhydrous knife or seed bed-openers) can be very significant and much deeper than at dry soil conditions. The reason for a high level of soil compaction at such moisture conditions is that soil aggregates will easily break down under a heavy load. The compression of soil particles will reduce soil porosity and reduce aeration that is essential for root growth and development and ultimately reduce yield. 

One study documented 18 to 27 bu/acre losses when corn was planted into wheel tracks of a susceptible wet soil during spring field work. Although yields over time may be reduced 4 to 6 bu/acre for corn and 2 to 3 bu/acre for soybean, yield due to severe soil compaction from disturbed soil operation can range from 10 to 30 percent or more depending on the level of soil compaction. These conditions can encourage shallow root formation.

Another problem that may be associated with wet soil condition planting is the proper seed depth, which should be on average a 2-inch planting depth to ensure best root formation. Therefore, check planter settings often and proper closing of soil is essential to ensure a uniform plant stand.

Low soil Temperature

Excess soil moisture can significantly affect soil temperature, especially in poorly drained soils.  The current moisture condition and the saturated soil profile caused significant drop in soil temperature from two weeks ago. Ideally, for optimum soil conditions for seed germination, soil temperature should be approximately 50 F or above at the top 2 inches. Some of the risks of planting in cold soils include a delay in germination and exposure of seeds to soil borne diseases that can have considerable impact on yield potential.

Soil erosion

Soil erosion is always a concern during this time of the year when soil, especially conventionally tilled fields, is most vulnerable without growing plant cover or residue cover, and exposed to rain intensity. Working soils during wet conditions can accelerate soil erosion due to soil compaction that reduces water infiltration and increases surface runoff. These freshly tilled soils are most susceptible to top soil loss during heavy rain events. It was documented that reduction of top soil depth (A-horizon) by 2 inches caused corn yield loss by as much as 2 and 5 bu/acre for loess- and till-derived soils, respectively.

Operating field equipment at suitable moisture soil condition is essential for maximizing yield potential and avoiding unnecessary soil compaction that can cause nutrient loss and deficiencies of nutrients such as potassium, and ultimately resulting in yield loss. Even delaying an operation part of a day to allow surface drying can make a big difference. Modern agricultural technology and equipment can make a difference in compensating for loss of time.



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. 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.

Corn Hybrids Adjust to Late Planting Dates

By Roger Elmore, Department of Agronomy

Three percent of Iowa’s corn lies quietly in the ground awaiting warmer soil temperatures (see USDA- NASS report). That contrasts dramatically with an average of 28 percent for the last five years and is hardly worthy of mention when contrasted with the record of 61 percent last year.  If temperatures warm as promised later this week, field work and corn planting will resume in earnest.

We still have time to plant corn in Iowa without sacrificing significant yield potential. On average, yields within 5 percent of maximum are still attainable in all but the north central and northeast regions of Iowa if we can plant by mid-May. In past research, this area shows a greater reduction in yield as planting is delayed presumably due to the limitations in growing season length. Regardless of the exact calendar date, maximizing harvestable yield depends upon soil conditions at planting and subsequent weather during the remaining growing season. In some rare situations, later planting dates produce more yield than early planting dates.

One thing discussed with later than normal planting is whether different hybrids should be planted to compensate for the later planting dates. For May planting dates, this is not normally necessary; hybrids adjust for delayed planting

To test this, I used a computer model, Hybrid Maize, to estimate physiological maturity dates of generic hybrids with relative maturities (RM) typically grown at either Nashua (NE Iowa) or Lewis (SW Iowa) (see Table). In both situations, hybrids matured before there was a significant probability of frost. Of course, along with delayed maturity, grain moisture will be greater with delayed planting.

We still have time to plant corn without significant yield losses. Adapted hybrids adjust to later planting by shortening the time necessary to reach silking. Farmers will want to plant longer season, adapted hybrids as soon as possible followed by mid- and shorter-season hybrids. Development and final yield of these hybrids will not be largely affected unless an early fall frost occurs.

Table. Effect of planting date on days to maturity (R6) and the probability of frost.  Two Iowa locations with hybrids of typical relative maturities (RM) for those locations.

† Days to maturity from planting and maturity date were estimated with Hybrid Maize corn modeling program.
‡ R6 is physiological maturity
§ Frost probabilities for Charles City (near Nashua) and Atlantic (near Lewis) from
Climodat, Iowa Environmental Mesonet.




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.

This article was published originally on 5/2/2011 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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