Wednesday, June 9, 2010

Short Corn on the Field Edge

You may have noticed how corn plants growing on the edge of a field always seem to be shorter than their neighbors. One of our local grad students proposed a particularly clever hypothesis today to explain it.*

Which got me thinking. I'd always assumed corn plants on a field's edge were shorter because they had greater access to light. Recently one of the blogs I follow proposed it was due to thigmotropism.** Thigmotropism is basically a plant's sense of touch. The physical push of wind makes many plants grow stouter than they otherwise would and is why the same type of tree gets shorter and craggier the farther up a mountainside it's found (not, as one hack "scientist" used to propose at forestry meetings, due to historic pruning acorn cultivation by Amerindians).

To clear this all up, I do what I normally do - I asked my boss. He didn't know himself but told a great anecdote from a meeting he once attended. The speaker had made some comment about light availability causing the shortness of field-edge corn plants when some cranky old dude from the audience interjected that it wasn't light availability at all - it was nitrogen availability. Corn plants in the middle of a field get a full dose of fertilizer spread all around and over them as the tractor makes multiple passes - plants on the edge get a lesser dose as no farmer wants to pay to fertilize the weeds or road on the edge of their field. Apparently you can see this effect further as nitrogen-rich effluent piles up on the low side of the field. I'm inclined to believe this explanation.

I love these practical, incredibly down-to-earth explanations for weird phenomena. I remember being out in the fields as a grad student, eagerly diagnosing "virus symptoms" all over the place with my classmates while the professors and farm advisers held their amusement, eventually correcting us with explanations based on herbicide drift and ozone pollution.

My favorite was this weird shaped dead spot on the edge of a field. Turned out, it was where the tractor turned around, applying too much chemical spray to the nearest plants in the process.

Never trust an ag scientist with clean boots!

*Which I'll post when he publishes it.
**I can't for the life of me figure out which blog that was.


  1. Dont forget about ground compaction from the tractors and equipment turning around...with perennial crops it is the pre-mature pull out of the ripper shanks that can lead to variability on the orchard ends.

  2. The blog you saw this in was probably The Garden Professors. If it was a result of underfertilization, compaction, etc. then it would not be seen at the edge of forests.

  3. hmm I thought it was the Garden Professors site at first too, but I'm pretty sure someone specifically drew the comparison to corn fields (checking the GP site again, they don't do that). Thigmotropism is a sensible explanation for the forest edge example, though I expect it's also partly due to light availability, humidity, soil moisture and temperature differences in this case. As they're conifers, it could also in small part be due to more exotic explanations like mycorrhizal differences.

    thanks though!

  4. Doc Almond:

    Great point! Soil compaction is as important as it is easily overlooked.

  5. From the above GP link:

    "Edge trees (or corn stalks) are more exposed and receive more wind, resulting in stunted heights and increased trunk diameter (you can't see this last characteristic in the Friday photo)."




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