Purdue University Department of Agronomy

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28 May 2012
URL: http://www.kingcorn.org/news/articles.12/HotDryMoreSame-0528.html
Departure from normal precipitation, May 2012
Fig. 1. Departure from normal rainfall, May 1 to May 27, 2012. Image source: Midwest Regional Climate Center. Click for larger image.

Hot & Dry; More of the Same Not Good for Corn Yield

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen at purdue.edu

Hot and dry; more of the same; second article in a week; worried growers; nervous markets; 8- to 14-day outlook not promising........

The talk uptown at Stu's Bar and Grill over the Memorial Day weekend revolved around the continued spell of hot and dry weather throughout most of Indiana and the possible effects on the yield of this year's corn crop. Some of the promise of the early-planted crop is withering away much like the corn crop in some fields that is already showing symptoms of wilting and leaf rolling. One of the regulars recalls hearing that some Extension corn guy at the university reminded folks a month ago that planting date is but one of a gazillion yield-influencing factors for corn and that a record early planting of the state's corn crop does not guarantee record high yields.

The bad news is that the crop is beginning to noticeably suffer in areas of the state. Plant mortality has reduced populations in some fields. Initial development of the nodal root system has been restricted in some fields. Leaf rolling (plant wilting) is occurring in some fields in corn that has barely entered the rapid growth phase. Many fields have yet to develop the healthy dark green associated with a crop that has entered the rapid growth phase, probably because their root systems are functioning poorly in response to the excessively dry soil conditions. The appearance and color of plants throughout many fields are extremely variable and painful for growers to look at.

So, what can be said about the effects of the continuing combination of excessively warm temperatures and dry conditions to date on the prospects for corn yield this fall? Well, we can describe the effects but it is difficult to predict the exact results on grain yield.

Grain yield in corn is the multiplicative result of plant population, kernel number per plant, and weight per kernel. The effects of stress on grain yield are determined by how the stress directly or indirectly affects these components of grain yield.

Effective plant population (plants with ears at harvest) is largely determined during the first 30 to 45 days after planting. Stand establishment this season in Indiana has been challenging for some due to cold injury, frost injury, fertilizer injury, soil crusting, seedling blights, and excessively dry surface soils. Stand loss due to excessively dry soils in early-planted fields is still possible if drought conditions worsen. Stand loss due to excessively dry soils is more likely for later planted fields whose younger plants may succumb to drought stress before their nodal root systems develop well enough to tap into deeper soil moisture. Indeed, reports of "rootless" or "floppy" corn have been coming in from a number of areas in the Midwest.

Much of the state's crop has reached the V5 leaf stage of development (5 visible leaf collars) or has progressed beyond this stage. The uppermost, harvestable ear is initiated by an axillary meristem of the corn plant at about V5. The potential number of kernel rows on that ear is determined by roughly leaf stage V7 (six to eight days after V5). Potential kernel row number is strongly determined by a hybrid's genetic background and is fairly resilient to the effects of stress. However, severe stress that occurs within the small window of time from V5 to V7 can indeed restrict kernel row number determination and is certainly a risk this year for crops under severe drought stress during those leaf stages.

Number of potential kernels per row on an ear is less of a genetic characteristic and much more influenced by growing conditions. This component of ear size determination is not complete until the V12 to V15 stages of leaf development and, thus, is vulnerable to potential stress over a longer period of time than is kernel row number determination. Consequently, severe and/or prolonged stress of any kind during this time period can restrict the potential length of the ears (i.e., fewer potential kernels per row).

While not actually a yield component, potential plant size is also largely determined during the vegetative period of growth prior to pollination. Severe stress of any kind during the rapid growth phase can result in shorter, smaller plants for the remainder of the season. Severely stressed plants also cannibalize lower leaves in an effort to remobilize nutrients to maintain the health of the upper canopy. The resulting smaller, less productive photosynthetic "factory" will be less capable of producing the photosynthate required during the important grain filling period after pollination and, thus, kernel weight may suffer even if conditions improve late in the season.

That just about sums up the short-term fearmongering for the 2012 Indiana corn crop. The good news is that the season is yet young and the return of moderate growing conditions could still turn around this crop. But time's awasting. The sooner the dry spell breaks, the sooner additional loss in yield potential can be avoided.

Pray for rain or turn on the irrigation.

Related reading.

Crop Management Information for Drought-Damaged Field Crops. Purdue Univ. http://www.kingcorn.org/cafe/drought [URL accessed May 2012].

Nafziger, Emerson. 2012. Root Problems in Corn Plants.The Bulletin, Univ. of Illinois. http://bulletin.ipm.illinois.edu/article.php?id=1650 [URL accessed May 2012].

National Drought Mitigation Center. 2012. U.S. Drought Monitor. http://droughtmonitor.unl.edu/ [URL accessed May 2012].

Nielsen, RL (Bob). 2007. Ear Size Determination in Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/EarSize.html [URL accessed May 2012].

Nielsen, RL (Bob). 2010a. Root Development in Young Corn. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/Roots.html [URL accessed May 2012].

Nielsen, RL (Bob). 2010b. "Rootless" or "Floppy" Corn Syndrome. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/FloppyCorn.html [URL accessed May 2012].

Nielsen, RL (Bob). 2012. Hot & Dry: Toll on Young Corn? Corny News Network, Purdue Univ. http://www.kingcorn.org/news/articles.12/HotDryYoungCorn-0522.html [URL accessed May 2012].

Wiebold, Bill. 2012. Early Corn Root Development. Integrated Pest & Crop Management Newsletter, Univ. of Missouri. http://ipm.missouri.edu/IPCM/2012/5/Early-Corn-Root-Development/ [URL accessed May 2012].

Wiebold, Bill. 2012. Rootless Corn. Integrated Pest & Crop Management Newsletter, Univ. of Missouri. http://ipm.missouri.edu/IPCM/2012/5/Rootless-Corn/ [URL accessed May 2012].