Skip Navigation

9/15/2008 - 9/21/2008

What is Needed to Maximize the 2008 Corn Crop

By Roger Elmore - Department of Agronomy
Iowa’s corn has experienced an unforgiving growing season.  With the last breaths of summer in the air many wonder what it will take to maximize yields from this date forward.  According to the recent USDA report, Iowa’s corn is about two weeks behind the five year average.  Eleven percent is ready for a frost, 71 percent is in the dent stage.  At beginning dent the crop normally needs about 3 weeks to mature.  The bottom line - regardless of location in Iowa, the corn crop needs a normal or later than normal frost date to maximize yields. 

Recall that planting dates were later than we would like to maximize corn yields, and that early-season growth was hampered by cold and wet soils.  Plant emergence was difficult and slow. Rainfall prevented timely post-emergence operations such as side-dress fertilizer applications and post-emergence herbicide applications.  Several articles in the ICM news document the season well.

Based on what I understand, cool temperatures after silking are necessary for maximum yields.  This happened in 2008. Indeed, slow heat unit accumulation rates characterize 2008 in Iowa.  The disadvantage of this is that slower crop development coupled with later than desired planting dates necessitates a long growing season, and a late frost.


An example from Central Iowa
A late August ICM News article, “Factors Needed to Maximize Corn Yield Potential in 2008”, suggested that to maximize yields in central Iowa, based on the Ames weather data through Aug. 22, large amounts of sunlight and rainfall after silking were necessary to maximize yields from that point forward; plus a late frost on or after Oct. 22. To some extent this has happened.  The crop nervously awaits a freeze – or at least those close to corn production feel that way! Figure 1 shows dates of 28 degree fall frosts for Ames.  The average date is Oct. 17.

To test this thinking, earlier this week I used Hybrid Maize, a computer model, with 2008 weather data through Sep. 15 for Ames. Table 1 shows a summary of the results.

yield table

If the weather after Sep. 16 is like of the median year for Ames, a crop could yield 91 percent of its normal potential, if there are no other limiting factors.  Based on Table 1 a maturity date of Oct. 28 is necessary for the highest yield potential with a frost date later than that.  This has happened in four of the last 30 years; 13 percent of the time (Figure 1).  In addition to a late frost, plenty of sunlight is necessary to maximize yields.  This week’s weather forecast is promising.

Iowa’s 2008 corn crop needs a later than normal frost date to maximize yield.  Conditions that hasten crop maturity from this point forward or an earlier frost will reduce yield potentials.

Ames frost dates


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

Nonconventional Soil Additives and Programs

by John Sawyer, Department of Agronomy

Every year products and programs are touted to Iowa producers as being the cure for crop production and economic woes. These seem to increase in number when crop prices are low or input costs are high. The old adage states “if it sounds too good to be true, then it probably is.” How do you know?

How do you know whether a particular product or program is a viable fertilizer and supplies crop nutrients, or has some proven effect on soil that will improve productivity or nutrient management? The standard advice is to demand unbiased research results that document all claims, and to discount testimonials. If well-documented research isn’t available, then be suspicious of seemingly extraordinary claims.

In Iowa, there are laws and rules administered by the Iowa Department of Agriculture and Land Stewardship (IDALS) for review and registration of fertilizer and soil conditioner products. So your first question should be, “Is this product registered for the claims made?” To find out, check with the IDALS Commercial Feed and Fertilizer Bureau by calling (515) 281-5321 or emailing .


According to the Iowa Fertilizer Law (Chapter 200), the definition of fertilizer is “… any substance containing one or more recognized plant nutrient which is used for its plant nutrient content and which is designed for use and claimed to have value in promoting plant growth …” Fertilizers have a guaranteed analysis that is “… the minimum percentage of plant nutrients claimed and reported as total nitrogen (N), available phosphorus (P) or P2O5 or both, soluble potassium (K) or K2O or both …”

According to the Fertilizer and Agricultural Lime Rule (Chapter 43), specific additional plant food elements beside N, P, and K can be guaranteed: calcium, magnesium, sulfur, boron, chlorine, cobalt, copper, iron, manganese, molybdenum, sodium, and zinc. There is a minimum analysis requirement (Table 1). For mixed fertilizers, the sum of the guaranteed analysis of total N, available P2O5, and soluble K2O must be 20 percent or greater. Thus, materials below these levels cannot be registered as a fertilizer; however, this rule does not apply to specialty fertilizers for nonfarm use or materials ordinarily applied directly to plant foliage.

                                fertilizer percentage table


Soil conditioners
According to Chapter 200, the definition of soil conditioner is “… any substance which when added to the soil or applied to plants will produce a favorable growth, yield or quality of crop or soil flora or fauna or other soil characteristics, other than a fertilizer, recognized pesticide, unmanipulated animal and vegetable manures or calcium and magnesium carbonate materials used primarily for correcting soil acidity.”  According to Chapter 43, product claims may be substantiated by one of two methods: 1) efficacy testing or 2) available research data relevant to Iowa crops and soils.

Efficacy testing information includes:

  1. Guaranteed ingredients;
  2. Crop or soil response measured;
  3. Research facility and investigators conducting trials;
  4. Dates and locations of trials;
  5. Trials conducted using the principles of experimental design and methods consistent with those in agricultural research, including raw data from proper treatment selection, replication, and randomization so that statistical analysis can be performed; and
  6. No consumer testimonials.

Fertilizer and soil conditioners submitted for registration may be required to be tested for a minimum of two growing seasons in at least three Iowa crop reporting districts. The results of testing are reviewed by the secretary's pesticide and fertilizer advisory committee.

The bottom line is to ask whether a product being promoted is registered with the state, and if it isn’t, then to question why and check with IDALS. Also, registrations can be reviewed to determine that a product meets the claims for which the registration was originally granted, and registrations can be cancelled if evidence exists that fraudulent or deceptive practices have been used.


Research Reports
A Web based comprehensive summary of research reports, titled “Compendium of Research Reports on Use of Non-Traditional Materials for Crop Production" are available for specific materials. The reports are maintained by the North Central Region Experiment Station committee NCR-103, “Non-Traditional Soil Amendments and Growth Stimulants."

The reports in the compendium are full-text searchable, so it is easy to locate reports on specific products or programs using the search feature. The compendium also contains regional extension publications covering specific products and programs. Those publications and other information on nonconventional additives can also be accessed through the ISU Agronomy Extension Soil Fertility Web site.

The regional NCR-103 committee also compiles electronic access to a listing of “Nonconventional Soil Additives: Products, Companies, Ingredients, and Claims,” product list. There is a link to this product list on the compendium Web site.


In summary
Be wary of products and programs with claims that seem extraordinary, relative to common wisdom and known research. In Iowa, we are blessed with highly productive soils that in general have many attributes to support good crop productivity, although they do often need fertilization and liming.

It is the rare soil amendment that might further enhance natural soil attributes. Supplementing the soil supply of crop nutrients when needed or replacing nutrients removed through crop harvest with guaranteed analysis fertilizer products, manure, or liming materials is a well-known and research supported activity. Attempting to change soils through soil amendments or specialty products for common field crop production typically is not well-documented and of uncertain economic benefit.



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

This article was published originally on 9/22/2008 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.