Too Many Plants Cuts Yields

Yield monitor dips in extra-thick stands.

Published on: Oct 21, 2008

The Corn Illustrated plots near Edinburgh, Ind., still await harvest. Since good drying weather has blanketed the region over the past month, odds are that the corn will be drier than anticipated when it is finally harvested, likely within he next two-to-three weeks. All of the plots except one are now totally brown. The high yield plot where about 250 pounds of nitrogen per acre was applied was still showing a greenish color in the stalks this week.

Meanwhile, farmer experiences are coming in. One report reaffirms what Dave Nanda believes the CI staff will see when they harvest plots. In the study where row width and population varies, some populations go as high as 55,000. Those plots were already lodging three weeks ago, notes Nanda, a long-time plant breeder and agronomist, now helping as consultant for the Corn Illustrated project.

In the farmer field, yields were above 200 bushels per acre, pushing 275 bushels per acre in spots. However, the farmer experienced problems with his planter in that field last spring. It was the first field he planted, and he was trying to get the bugs out of a used planter. Because the drives were acting up, he had to replant small areas on certain rounds. Where he replanted, final stands were near 70,000 plants per acre.

Nanda firmly believes that someday you or your children will plant at rates that thick. However, hybrids will be bred to take it, row spacing will be such that it allows equi-distant spacing, and it's even possible that plant breeders and geneticists may redesign the corn plant into a structure that maximizes capture of light in a setting where plants are that close together. Meanwhile, ending up with stands where plants are that thick, especially in 30-inch rows, can put undue stress on plants. Undue stress usually result sin smaller ears, more plant lodging and perhaps overall lower yield.

All three were true in the farmer report forwarded to us recently. Stalks were spindly, and lodging was already a problem, although it was not so bad that it was yet rated severe. Ears were smaller than you typically see since there were so many of them, per acre. And whenever the combine hit those thick patches in the field, you could count on the yield monitor dipping as soon as it registered the yields coming from those parts of the rows.

In fact, it wasn't a gradual drop. Yield dipped 25 to 35 bushels per acre, depending upon the pass and position in the field. But even in higher organic matter, heavier clay loam soils, the yield monitor displayed numbers that meant you were raking in up to $100 less per acre in gross revenue, just because the corn was too thick. Conversely, planting that many seeds per acre of expensive GMO triples would mean spending money on more seed than you need.

The message was clear - overplanting when it goes to extremes can harm yields, not help them. Unnecessary stress likely explains why actual yields dip. And even without a yield decrease, profits would dip because extra seed means extra expense in more dollars than necessary paid to the seed company.