Dr. Dan Talks Agronomy

Take On Two Ears

The better to 'ear' you with? Farmers are reporting more multiple ears this year. Does it mean more yield? (DTN photo by Pamela Smith)

I walked my corn fields recently and couldn't believe my eyes. Eight out of 10 stalks sported two ears and perhaps as many as one of 10 had three ears. Most years, a single ear on a stalk is normal and if we get a second ear, it is small or barren.

Are two ears better than one? Is it a sign of too little population? Or is this just an extraordinarily good year when the additional ears will result in a significant yield bump?

Corn yield depends on number of ears per acre, number of kernels per ear, and average weight per kernel. However, number of ears seems to be the biggest factor in final yield -- that's why farmers have been pushing populations to 30,000 plants per acre and beyond.

Grasses are an interesting species. Wheat, for example, has a potential tiller bud at the base of every leaf, but most aren't expressed. Corn has an ear bud at the base of every corn leaf, but most aren't expressed. Grass plants have the ability to suppress and control the release of these embryonic buds -- a phenomenon called apical dominance. Cut off the top bud on a soybean plant or dingit with Cobra and you will get more branching because you shut down the apical dominance.

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Typically, corn forms only one ear and wheat forms two tillers per plant under field situations to make sure they can fill out these seed-bearing structures. Seed companies have selected corn hybrids that generally have one large ear under normal farming practices.

Years ago, I did a study as part of my graduate research with wheat in the field, greenhouse, and artificial growth chamber and also true hydroponic media in a growth chamber. What I discovered (and published) was that I could get a wheat plant to tiller excessively by eliminating stress and any competition for light, nutrients and water. Tillering dropped off when I began to bring back competition. I concluded that tillering was naturally controlled to some degree, but that control was circumvented to some extent by removing competition or stress. However, later tillers, while impressive in number, never contributed more than 10% of the total final yield. The spike on the main stem or the spike on the first and second tiller determined final yield.

Corn seems to act in a similar manner. Emerson Nafziger, University of Illinois agronomist, said: "Both weather and management exert more influence [on ear count] than genetics at the low population extremes, while genetics control and maintain ear count at normal and high populations. We see low rates (less that 2% to 3%) of stalk barrenness among today's hybrids and populations (up to 50,000) which confirms that breeding has mostly eliminated this as a potential problem."

Many cornfields are deep green in color and very healthy this year, indicating a lack of stress or competition for resources at normal plant populations. Under these very good conditions, plants can produce a second ear. "Properly managed corn shouldn't have many two-eared plants, but I've heard there are fields this year under outstanding conditions in which quite a few plants, and greater than 25% in some cases, have a second and smaller ear with grain," Nafziger told DTN.

Nafziger suggested that the abundance of double ears could be due to genetics that limits expansion of the primary ear, so the only outlet for the sugars produced by photosynthesis is developing a second ear. Generally, second ears are either barren or produce only 5% to 10% of the grain of primary ear. However, in a year like this, that second ear could contribute a significant amount of yield if stress remains abated throughout the summer.

If you are noticing a lot of second ears that are filling, take a look at the first ear and see if it's filling to the tip. Lack of tip back suggests you should consider increasing the population another 1,000 plants per acre next year. However, given such an exceptional season to date, lack of tip back and appearance of a second ear that is filling, suggests the crop is producing much more sugar than normal and not losing it during warm nights due to dark respiration.

This year, two ears might just be better than one.

Dan Davidson can be reached at djdavidson@agwrite.com

(PS/AG)

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