Purdue University Department of Agronomy

Corny News Network

Published 3 Aug 2009
URL: http://www.kingcorn.org/news/articles.09/CropProgress-0803.html

A Tale of Three Cropping Seasons

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen at purdue.edu
Silking progress
Fig. 1. Corn silking progress in
Indiana for select years. Click on
image to view larger version.

Maturity progress
Fig. 2. Corn maturity progress in
Indiana for select years. Click on
image to view larger version.

Fig. 3. Corn grain yield relative to
historical trend line for Indiana in
1992, 2002, and 2008. Click on
image to view larger version.

The summer of 2009 in Indiana will likely go down on record as one of the coolest cropping seasons in recent history. July went into the record books as the second coolest July since 1871 (WISH-TV, 1 Aug 2009). Coupled with the significant delay in planting progress, the current slow pace of crop development has generated a lot of coffeeshop talk about what impact there will be on corn grain yield and whether there is a significant risk of some of the crop not maturing safely before a killing fall frost.

History is often not a reliable predictor of the future, but looking at similar instances of slow crop progress in the past can sometimes offer a glimpse of the future possibilities. There are three such similar instances of slow crop progress in Indiana beginning with 1992.

Silking progress that year, again in 2002, and again in 2008 occurred at similar late calendar periods (Fig. 1). Compared to the current 5-year average pace, silking progress in all three of those cropping seasons was about two weeks behind average. As the crop moved through the remainder of the grain filling period, crop progress all three years continued to lag behind the 5-year average; though the 2002 season matured slightly ahead of the 1992 and 2008 seasons (Fig. 2). Crop maturity for those three years occurred one to two weeks behind average.

So, what is the point of all this? Simply put, the current 2009 silking progress for corn in Indiana is nearly identical with that exhibited by the 1992, 2002, and 2008 crops (Fig. 1). If this calendar lag continues, the 2009 corn crop will also likely mature at least two weeks behind the 5-year average (Fig. 2). Maybe the eventual grain yields recorded for those years can provide us with a hint of the future to come?

Or, maybe not.

The statewide average corn grain yield in 1992 for Indiana was 16.4% above the historical trend; the largest positive departure from trend since 1942. Conversely, the statewide average corn grain yield in 2002 for Indiana was 15.3% below the historical trend; the largest negative departure from trend since the drought of 1991. Finally, statewide average corn grain yield for Indiana last year (2008) was slightly (4.8%) above the historical trend yield.

So, what are we to make of three cropping seasons whose crop progress was so similarly delayed, yet which eventually ended with statewide grain yields so dramatically different? As I often like to remind folks, there are a gozillion factors that influence grain yield in corn. Ultimately, grain yield represents the complete integration of effects from every yield influencing factor that occurs throughout a particular cropping season. Delayed crop progress is but one of many such yield influencing factors.

The slow cropping season of 1992 was indeed a cool summer; best remembered by those of us "long in the tooth" for the unusually late killing freezes of June 21 and 22 that devastated crops throughout northern and westcentral Indiana. The remainder of the summer was also cool with August ending up as the 5th coolest August since 1900. Rainfall was not lacking and, if anything, was a bit excessive throughout much of the summer. AND YET.... the corn crop responded with yields that far exceeded anyone's imagination. Lack of heat and drought stress on a late crop was a real advantage that year.

By contrast, the 2002 crop got off to a slow start with very delayed planting statewide. However, rather than a cool summer, the 2002 cropping season was characterized by very hot and dry conditions from late June through at least mid-August. The warm temperatures helped the crop make up for some of the delayed planting, but still matured about one week behind the 5-year average. One of the key yield influencing factors in 2002 was the combination of delayed crop development (especially silking and early grain fill) and hot, dry stressful conditions in late July and early August. Knock on wood, but Indiana corn fields have escaped that damaging combination in 2009 to date.

The 2008 crop was similarly delayed in its progress throughout the year but experienced more of a "mixed bag" of weather, ranging from enough moisture and moderate temperatures to too little moisture and hot temperatures. The "mixed bag" of weather conditions played a role in that late-developing crop achieving slightly above average yields (4.8% above trend).

Bottom Line

The current corn crop is moving out of the important pollination period and into the equally important grain filling phase. It is true that this year's late corn planting and uneven stand establishment are not favorable for optimum yields, but it is also true that most of the state's crop has, so far, escaped serious stress from drought, heat, disease, and insects.

Moderate temperatures and adequate moisture during the grain fill period are favorable for kernel set success and kernel weight development. For what it is worth, the percentage of the 2009 Indiana corn crop rated by USDA-NASS as good to excellent has consistently been in the low 60's since early June (only slightly below those of the 2008 crop). Based purely on the historical relationship between July crop condition ratings and statewide grain yield, such ratings would predict trend line yield (aka average yield) for Indiana's corn crop this year.

The remainder of this season will greatly determine eventual yields of this year's corn crop. Two major hurdles remain for this year's crop. One is to avoid serious heat/drought stress for the remainder of August and the early part of September. The other is to avoid an early killing fall frost in late-planted fields not yet physiologically mature (kernel black layer), but it is too early to predict the probability of that risk.

As the old saying goes...."The opera ain’t over until the fat lady sings."


Nielsen, RL (Bob) 2009. Cool Temperatures: Good News or Bad News for Corn? Corny News Network, Purdue Univ. [online] http://www.kingcorn.org/news/articles.09/GoodNewsBadNews-0721.html [URL accessed 8/3/09].

Nielsen, RL (Bob). 2009. Corn Planting Date is Important, But.... Corny News Network, Purdue Univ. [online] http://www.kingcorn.org/news/timeless/PltDateCornYld.html [URL accessed 8/3/09].

USDA-NASS. 2009. Crop Progress. USDA National Ag. Statistics Service. [online] http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1048 [URL accessed 8/3/09].

USDA-NASS Indiana. Indiana Reports and Statistics. USDA National Ag. Statistics Service. [online] http://www.nass.usda.gov/Statistics_by_State/Indiana/index.asp [URL accessed 8/3/09].