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6/23/2008 - 6/29/2008

Yellow Corn, Wet Soils, and N Loss – Part 2

by John Sawyer, Department of Agronomy

Last week (June 19) I provided some observations on corn growth and response to nitrogen (N) applied in an anhydrous ammonia study being conducted at the ISU research farm between Ames and Boone. Following are some observations one week later (June 26, 2008).

Response to Anhydrous Ammonia Timing – More Observations
In this study, anhydrous ammonia is applied in late fall (Oct. 31, 2007), spring preplant (April 30, 2008) and sidedressed (June 18, 2008) at different depths of injection and application rates. Corn was planted May 15. The study is “low” on the landscape, and like many fields this year part of the study area was wetter than the rest, with a small part where the corn is dead due to standing water.

Plant growth has progressed a growth stage or two since last week. As of Thursday, June 26, the corn on the “higher” ground continues to grow better and respond more to applied N than plants on the “lower” ground or where plants were severely impacted by wet conditions. However, plants on the lower ground are now responding to the fall and spring applied N, where they did not show this response a week ago.

Looking at the plant coloration and growth, I generally still see a better response to the spring applied ammonia compared to the fall applied ammonia, especially at lower N rates. It is still too early to tell what amount of N may have been lost this spring, but the corn coloration is beginning to show the classic response to N rate (with more differentiation between rates where corn is growing the best). In this study there are two depths of injection. In the lower part of the landscape, the N response appears better with the shallow ammonia placement. This is likely due to the N being placed closer to the root system, especially where the root growth into the soil was restricted by wet soil.

As the corn continues growth I would expect to see more differentiation between N rates. Also, experience with N rate studies would tell me that the low N rate (80 lb N/acre) would not be an adequate rate even in a “normal rainfall” year. And, in this wet year, experience would indicate that the N response will be greater than normal and to a higher required N rate. Over time, as the plants grow and demand more N, this will become more clear.

The corn has not responded yet to the sidedressed ammonia. There was no rain from the time of sidedress application to the time I evaluated the corn this week. While I was evaluating the corn I got rained out of the field. Following that precipitation and with additional root growth, I would expect the corn to now begin accessing the sidedressed N.

Yellow Corn & Nitrogen Figure 1

Figure 1. The middle orange stake is in the border between two four row plots. The plot on the right (stake is in the middle of the plot) had no N applied and the plot on the left (stake is in the middle of the plot) had 80 lb N/acre applied last fall. (J.E. Sawyer, June 26, 2008)

Yellow Corn and Notrogen Figure 2

Figure 2. The middle orange stake is in the border between two four row plots. The plot on the left had no N applied and the plot on the right had 160 lb N/acre applied last fall. (J.E. Sawyer, June 26, 2008)

Yellow Corn and Nitrogen Figure 3

Figure 3. The middle orange stake is in the border between two four row plots. The plot on the right (stake is in the middle of the plot) had no N applied and the plot on the left (stake is in the middle of the plot) had 80 lb N/acre applied last fall. The plot to the extreme left had 160 lb N/acre applied last fall. These plots are in the area with best corn growth. (J.E. Sawyer, June 26, 2008)

John Sawyer is a professor of agronomy with research and extension responsibilities in soil fertility and nutrient management.

Corn Yield Predictions for Replanted and Late-planted Fields

By Roger Elmore, Department of Agronomy

The June 23, 2008 USDA report stated that 11 percent of Iowa’s corn crop was replanted or is to be replanted. Eight percent was flooded.  Governor Culver declared on June 20 that three million acres of our corn and soybean acres were damaged by the floods. 
Many things come to mind when we consider replanting any crop, let alone corn in late June.  Replanting corn this late is typically not recommended. Extension publications from previous years often say something like this, “As planting is delayed, the yield potential of corn declines at a faster rate than soybeans.  In most cases the relative advantage will move to soybeans after approximately June 10 to June 15.”  

So, why are producers even thinking about replanting corn? A one word answer -- Economics. Never-before seen corn prices challenge our conventional thinking.

Summary of Previous Research
Guidelines for replanting  are posted on our Web site.  One variable important in any replant decision is what yield to expect.  Estimated yield based on planting date and final population is listed in a table in the Corn Planting Guide. Using this information, we find that 52 percent relative yield potential is possible with a population of 32,000 plants per acre when corn is planted between June 24 and June 28.  This table was based on research conducted in the late 1990’s combined with previous data.

Garren Benson, retired ISU Extension corn agronomist, reviewed planting date experiments and summarized the findings in 1990 (Table 1). Regardless of hybrid maturity, yields when planted on July 1 ranged around 30 percent.  Earlier maturing hybrids resulted in drier grain at all planting dates, but early maturing hybrids also yielded less than adapted full-season hybrids especially if planted on or before June 1.

Table 1. Influence of planting date and hybrid maturity on corn grain yield and harvest grain moisture in north central Iowa. Maximum yield in this table was 144 bu/acre.  Table adapted from Benson, 1990.†

Plant Date and Hybrid maturity Table

† Benson, Garren O. 1990.  Corn replant decisions: A review. J.Prod. Agric. 3:180-184 (1990). 

With either late planted corn or replanted corn, an early fall frost can destroy or dramatically reduce seed yields. Table 2 summarizes locations and years which had either a late frost or an early frost in Benson’s series of trials.

Table 2. Impact on corn grain yields and harvest grain moisture when fall freeze was 3 weeks later or 2 weeks earlier than normal in north central Iowa. Maximum yield in this table was 148 bu/acre. Table adapted from Benson (1990).

Grain Moiture Table 2
† Benson, Garren O. 1990.  Corn replant decisions: A review. J.Prod. Agric. 3:180-184 (1990). 

‘Adapted’ hybrids in these trials were likely between 105 and 110 days relative maturity; ‘early’ hybrids were likely 10 days earlier, and ‘very-early hybrids’ 15 or more days earlier. Year to year variability among hybrids was much greater for later planting dates than for early planting dates. Early frosts profoundly affected corn yields and grain moisture contents. For example, an adapted hybrid planted on July 1 yielded 61 percent of optimum in years with a late frost, but only 7 percent in years with an early frost.

Computer Simulations
Iowa research on extremely late planting dates is limited to Tables 1 and 2; most efforts center on yield response to earlier planting dates. Much effort though has focused on developing computer simulation models to predict corn yield. I used a corn simulation model, Hybrid-Maize developed by colleagues at the University of Nebraska, here to estimate effects of late planting dates with different combinations of hybrid maturities at three Iowa locations. As the developers of the model caution, “…the results of model simulations should be considered approximations and not taken as fact.” The model will help us meet our objectives of estimating yield potential and assessing the risk of frost associated with late planting.

Background information on the variables used in the Hybrid-Maize model relative to planting dates and hybrids used for each location are shown in Table 3.

Table 3. Variables used in Hybrid-maize simulations. Constants in all of the simulations were optimal water during the growing season, a seeding rate of 30,000 plants per acre, and a seedling depth of 1.5 inches.

Hybrid Maize Simulations Table
† These years of actual weather data were used to simulate corn responses at the different locations.
¶ Hybrid growing degree day (GDD) requirements/ approximate crop relative maturities in days.
§ Assumes a 90 day hybrid adjusts for late planting dates by shortening GDD requirements. I only ran this comparisons at the Nashua location.

Data in Table 4 show a full-season (early planting, full-season hybrid) simulation coupled with a June 30 planting with either an early or very early hybrid. Late-replant yields in seventy-five percent of the years will range from 50 to 60 percent. Yields of 60 to 70 percent are possible in the very best years.

Thus, if a field near Ames normally produces a full-season crop yield of 200 bu/acre if planted on June 30 with a 2160 GDD hybrid, we might expect 100 bu/acre in an average year, 140 bu/acre in an extraordinary year, and in the worst year, 28 bu/acre. The chance of frost at maturity for this planting is 39 percent, or about two years out of five.

Table 4.  Early planting with full-season hybrids compared to June 30 planting with early or very-early hybrids at three Iowa locations.
Early Planting Full Season Hybrids Table

These data are also shown graphically in Figures 1–3 along with all of the other simulations at the three locations.The figures show the effect of delayed planting yield potential (as a percent of maximum).

The top end of each bar in the figures represents the best yield in the years modeled (21 years for Ames and 19 for the other two locations). The bottom end of each bar represents the yield that could occur in the worst year. The lower horizontal line of the box represents the 25 percentile limit, and the upper horizontal line represents the 75 percentile limit. The circle represents the average year in the simulation. The figures display the range of and consistency of reaching certain yield potentials. Crawfordsville, Iowa Hybrid-Maize Estimate Table

Ames, Iowa Hybrid-Maize Estimate Table

Nashua, Iowa Hybrid-Maize Estimate Table

Figures 1 – 3. Hybrid-Maize estimates of yield potentials for the various planting date/hybrid combinations at three Iowa locations showing the effect of delayed planting yield potential (as a percent of maximum). Data were simulated using Hybrid-Maize, University of Nebraska.  The relative planting dates for all locations were the same: E = 25 April; M = 20 June; L = 30 June.

Probabilities of frost at crop maturity as well as silking and maturity dates are shown in Table 5 for the complete set of computer simulations.

Table 5. Silk & maturity dates and frost probabilities at maturity for all the combinations of planting date and hybrid for three regions of Iowa. Dates listed are based on Hybrid-maize simulations of the median year in the weather data set provided for each location as noted in Table 3. The ‘median year’ is apt to differ in each of the six to seven simulations developed for each location. This is because the year to year ranking in the simulation model is based entirely on estimated yield. Probabilities of frost of less than 29 degrees F are from ISU’s Iowa Environmental Mesonet.

Table 5

†The first letter of these pairs reflects the planting date: E=25 April; M=20 June; L=30 June.  The second letter of the pair refers to the hybrid planted: F=full-season; E= early-season; VE = very-early season. Specific hybrid characteristics varied with location as shown in Table 3.   

To help explain the simulation findings, here is an example from Figure 2:  In the best year a full-season corn replanted in central Iowa (around Ames) on June 20 could yield about 70 percent of normal while in the worst possible year it might yield less than 10 percent of normal. Interestingly though, yields are less than 50 percent of normal only 25 percent of the time.

On the other hand, if an early hybrid is planted on June 20, not only will yields in the best year be higher, 77 percent, but also the estimated yield in the worst years will be higher, 29 percent, than if a full-season hybrid was planted this late.

The figure also shows a reduced range of yields associated with planting an early-season hybrid on June 20 relative to an adapted hybrid planted at the same time. Planting an early-season hybrid also reduced the probability of frost by 68 percent (Table 5). The decision on June 20 is apparent: plant an early-season hybrid. The choice for a June 30 planting date at the same location is not as apparent. Although yields in the best of years are less with the early hybrid, the risk of achieving yields less than 47 percent of normal are much less and the frost risk is also reduced by 47 percent.

Table 6 summarizes previous research with Hybrid-Maize simulations. Yield potential from the Corn Planting Guide is an average for all years, statewide. Benson’s data (from north central Iowa) and the Hybrid-Maize simulations allow fine-tuned comparisons given specific types of years. Averages of the latter two, 33 percent and 43 percent, are less than that provided by the Corn Planting Guide.

Simulated results compare well with those of Benson especially when early or very early hybrids are used.  In a year with poor conditions or with an early frost, early-season hybrids planted in late June may yield as little as 22 percent of normal potential.  But, with a late-frost or excellent conditions, yields may reach 60 to 67 percent of potential.  Average performance for these situation ranges between 40 and 50 percent.

Table 6. Summary of findings from previous research and from Hybrid-Maize simulations.
Summary Findings Table

†Freeze dates and data for Benson 1990 data and are from Table 2/ Worst and Best years of simulations are from Hybrid-Maize (Figures 1-3).
¶”Adapted’ hybrid/ ‘Very Early’ Hybrid (see Table 5 footnote for full description).
§ from Table 1.
‡ from Table 2.

Concluding Remarks and Cautions
The decision to replant in late June is not an easy one. The simulations provided here are approximations of what might happen given multiple scenarios based on the last two decades of weather data.  Yet, they seem consistent with previous research. 

In late-June replant situations, plant hybrids that are 10 and 15 days earlier than hybrids typically used in an area. Shortening RM by 10 to 15 days equates to a reduction of approximately 400 to 500 growing degree days. When growing short-season hybrids, remember they were not developed for Iowa. Because of this they may not be able to tolerate environmental stress, insect and disease pressure quite as well. Fortunately, hybrids in these maturity ranges are available for planting.

Nevertheless, whether corn is planted for the first time or replanted between now and June 30, plant early-season hybrids. These will have the greatest chance of maximizing yield while lowering risk of very poor yields.  Be aware that the fall frost risk associated with planting these hybrids late will range between 29 and 39 percent in the south and central regions and up to 66 percent in the north.
Given the high prices of not only corn but also soybeans and other commodities, take care in evaluating all options: replanting with corn, soybeans, grain sorghum, or various spring and summer annual forage crops, or leaving the land fallow. In any case, consider carefully your crop insurance options. This is a time for logical, thoughtful decisions based on sound advice and careful calculations.

Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production.

Dealing with Late Weed Escapes in Corn

by Bob Hartzler, Department of Agronomy
While herbicide advertising often talks about full-season weed control, we really only need herbicides to control weeds until the canopy has developed sufficiently to suppress any late-emerging weeds. Iowa State University research found that less than 1 percent of the waterhemp emerging at the V8 corn stage survived.  While there was higher survival at earlier emergence dates, biomass and seed production of waterhemp emerging at the V5 corn stage was suppressed more than 90 percent compared to plants emerging with corn.

Many corn fields across the state are likely to have greater problems with late-emerging weeds than normal.  There are two primary causes for these infestations:  1) the heavy rain in May and early June will reduce the length of control provided by residual herbicides, and 2) poor canopy development due to cool temperatures, saturated soils and reduced stands will provide a favorable environment for weed growth.

Fields should be carefully evaluated prior to spraying weeds in large corn.  Weeds that emerge significantly later than the corn (anytime beyond the V3 stage) are at a tremendous competitive disadvantage with the crop due to the crop’s head start. While these weeds may survive and produce seed, their impact on the corn yield should be minimal unless they are thick enough to create a sod. Thus, if you have 3 to 4 inch weeds in 30 inch corn it probably does not warrant an additional weed control trip.  Spraying corn beyond the V8 stage may cause more damage to the crop than would be gained by eliminating late-emerging weeds.  Most importantly, the majority of herbicide labels prohibit application to larger corn due to problems with crop tolerance or efficacy. (See Corn Size Restriction for POST Herbicides).  Glyphosate restricts applications to corn less than the V8 stage or 30 inches in height.

While everyone likes to see a weed-free field at harvest, sometimes it is best simply to live with the hand that has been dealt.  While late-emerging weeds in most fields are unlikely to impact yield, the seed produced by these plants will increase weed densities the following year.  This increase in weed populations should be taken into account when developing weed management plans for 2009.

Bob Hartzler is a professor of weed science with extension, teaching and research responsibilities.

Flooding and Stored Grain

By Charles Hurburgh, Department of Agricultural and Biosystems Engineering and Dan Loy, Department of Animal Science


Floodwaters have soaked many grain bins on farms and at commercial elevators. With only a few exceptions, flood soaked grain is not useable for feed or food. Flooding affects both the stored grain and the storage structures.


Grain and Grain Products

Flood damaged grain is adulterated grain because of the potential for many contaminants to enter through the water. This grain should be destroyed, never blended. Contact local public health and sanitation officials for the best disposal process in your area.


Water coming up from tiles and pits is just as suspect because storm and sanitary sewers are usually compromised in floods.  Even field tile water may contain animal waste products, high chemical levels and other contaminants. 


Corn will stay at 30 percent moisture after the water drains off; soybeans about 25 percent moisture.The moisture won't travel more than a few inches above the floodline.


Good grain on top of flooded grain must be removed from the top or side, not down through the damaged grain. Remove all the good grain possible before doing anything with the bad portion.


Toxins are likely in rewetted grain. Warm wet conditions are ideal for mold growth. Soaked grain will spoil within a day or two at high moisture and summer temperatures.


Rain damaged grain (ie: roof taken off) can be saved by drying and cleaning. This grain should be tested for mycotoxins before use. Use reconditioned grain immediately.


Take care not to track or mix mud or gravel from flooded grounds into good grain during salvage operations. These materials are potentially toxic for the same reasons as the floodwaters.


FDA allows for reconditioning (washing and drying at high temperatures) in cases where the flood water did not remain long and it is known that the water did not contain contaminants This situation would be very rare, to know that floodwater was clean.



Grains swell when wet so bin damage is likely; more so with soybeans. Bolts can shear or holes elongate. Look for signs such as stretched caulking seals, doors misaligned or similar structural problems.


Check bins with stirring devices carefully. The bin must be perfectly round for them to work correctly.


Bin foundations can shift, float or deteriorate from flooding.  Inspect structures and foundations carefully, and have an engineering evaluation for larger bins.


Expect electric wiring, controls and fans to be ruined. Do not energize wet components. Be sure the power is off before touching any electrical components of flooded systems.


Wood structures will be hard hit and may retain mold and contaminants.


Clean facilities and ground completely. Then do a careful food safety inspection before returning facilities to operation. Maintain clean records.



In the rare situations where the water was not contaminated, the grain may be reconditioned. If the grain is to be sold, reconditioning has to be done with the written consent of FDA. For feed on site, producers have three alternatives.

  •  Dry the grain
  •  Feed it immediately to their livestock
  •  Ensile the grain for livestock feed.

Decisions need to be made quickly. The good grain should be removed immediately, again not down through the soaked grain.  No flooded grain can be sold to the market without approval of FDA, to document its reconditioning and intended use.


There is no problem, other than spoilage within a day or two, with using uncontaminated soaked corn as a livestock feed. Just replace the corn in the animals' current diet with the wet corn. Remember to adjust amounts fed for moisture.


Wet, whole soybeans can be fed to cattle if the soybeans are limited to 10 to 12 percent of the ration's dry matter. Soybeans substitute well for the protein in soybean meal, but they need to be fed with a vitamin-mineral-additive premix if substituted for a complete protein supplement.


It is not necessary to heat-treat the soybeans for cattle. Also, if adding whole soybeans to diets high in distillers' grains, watch the total ration fat content. For hogs, raw soybeans can only be fed to mature sows. The soybeans need to be heat treated if fed to younger pigs.


Charles Hurburgh is a professor of Agricultural and Biosystems Engineering and professor in charge of the Iowa Grain Quality Initiative. Dan Loy is a professor of animal science with research and extension responsibilities for livestock nutrition.

ISU Crops Webcast from ISU Extension

By Doug Cooper, Extension Market News

A weekly Extension crops and weather audio webcast is available on the Market News Audio page. The webcast is produced and published on Monday afternoons, with Doug Cooper leading a discussion of current Iowa agricultural concerns with Elwynn Taylor, Rich Pope and other Extension Specialists. 

Flooded fields: all too common
Flooded fields are all too familiar. (Photo by Palle Pedersen)

The weekly Webcast is accessible from the ISU Extension Market News Audio page.

This week's webcast (click here to access) (Time 45:07) was produced  June 23. Elwynn Taylor, Iowa State University Extension climatologist; Rich Pope, program specialist and Ken Holscher, entomologist discuss the aftermath of the floods and excessive rainfall that has delayed the growing season for farmers. Holscher says mosquito populations will depend on the weather the next few weeks.

In addition, the latest Iowa Crops & Weather report indicates 50 percent of the corn and soybean crops are in good to excellent condition as of Sunday, June 22.

 Listeners may ask questions for discussion during next week's webcast by clicking on the link:

Doug Cooper is the ISU Extension market news director

Avoid Unnecessary Tillage in Wet Soil Areas

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

The unavoidable and extreme wet conditions we are experiencing this year present soil management challenges, especially in low and poorly drained fields where a significant portion of the field is under water. The flooding conditions and super saturated soils are causing significant changes in physical, chemical, and biological properties of the soil. The immediate impact the wet conditions have is the prevention and delay in planting wet areas of the fields.

There may be an attempt to till such areas when the soil appears to be dry, but even though the soil surface looks dry there will be a significant amount of moisture below the top two inches. Tilling the soil will do more harm than good by compacting soil and creating conditions that will effect root development and induced soil erosion.

Farmers planning late-season planting in wet areas should avoid tillage before planting in most instances. Sun and warm air temperatures at this time of year effectively dry the surface as well or better than tillage in many instances. Tillage in wet, heavy soils tends to produce clods and destroys residue cover needed for erosion protection from early summer rainfall.

Emphasis should be concentrated in the remaining window of time on the planting operation, making planter adjustments as needed to compensate for wet soil conditions. Check for uniform seed depth and lighten pressure on closing wheels and depth-gauging wheels to only the level necessary to maintain desired seed depth and seed-to-soil contact. Be sure to evaluate yield potential, environmental conditions, and other factors in the farm business when contemplating a planting in late June.

How this soil saturation will influence next growing season
The long-term damages to soil quality in areas where significant flooding problems have taken place need to be considered during the next season planning. Several changes will take place when soil is under saturated conditions for an extended period of time and can carry over to the next season.

One of these potential changes is the change in biological health of the soil, especially if the soil is left unplanted. This affects the health of the microbial community, which is essential to nutrient cycling. The existence of plants in such areas will help enhance the development of microbial community, even though planting late will have significant yield reduction.

The other main issue farmers need to consider for the long-term impact of flooded areas is to carefully evaluate the status of nutrients next season by taking soil samples from the flooded areas. Assess the content of major nutrients such as N, P, and K and correct the potential deficiencies of these nutrients by applying the proper rates for the next season.

The flooded fields need to be managed carefully. Avoid any extensive tillage that may compound the problem by creating soil compaction that will reduce water penetration and increase potential soil erosion. The lessons of such wet conditions are to evaluate the field conditions and assess the needs for implementing management practices that will minimize such impact in the future. It will be timely to evaluate the need for installing tile drains or grass water ways to help remove access water from fields in the future.

Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science

A Cool and Thankfully Dry Week

By Rich Pope, Department of Plant Pathology

Some good news this week, with much-needed access to fields gained across Iowa. Also on the positive side, hay harvest progressed rapidly and hay yields were reportedly good.

Although the week was a bit cooler than average, the dry weather was a welcome relief.

Degree day accumulations by Crop Reporting District

The big three agronomic questions facing Iowa remain weed control issues, nitrogen fertilization concerns related to the flooding and saturated soils, and replant decisions. In some cases, agronomically sound decisions have been tempered by pressure for corn production arising from contract agreements. Early frost concerns increase more each day with mid-to late-June planted or replanted corn.

Rich Pope is an extension specialist with responsibilities in the Corn and Soybean Initiative.

Field photo by Tim Chwirka

This article was published originally on 6/30/2008 The information contained within the article may or may not be up to date depending on when you are accessing the information.

Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.