Yield increases resulting from higher plant populations are primarily the result of increased light interception during grain fill by the crop canopy.

Optimum plant population varies little with planting date or row width, but early-maturing hybrids may require a higher plant population than full-season hybrids.

While the economically optimum plant population varies according to the cost of seed and the price of corn, the plant population needed to maximize profitability ranges from about 32,000 to 34,000 plants per acre under current economic conditions.

Planting date has a large impact on corn yield. When compared to an early-May planting date for a population of 32,400 plants per acre, our results from 2008 at Lamberton and Waseca show that yield was reduced by three per cent and 17 per cent when planting was delayed until mid-May and late May, respectively.

Research results show that as plant population was increased from 15,600 to 32,400 plants per acre, canopy light interception increased from 82 to 92 per cent and grain yield increased from 157 to 190 bushels per acre. However, as plant population was increased from 32,400 to 43,600 plants per acre, light interception only increased from 92 to 95 per cent, and grain yield increased by just one bushel per acre.

Plant population should be managed with the goal of optimizing light interception. Light interception during grain fill can be evaluated by looking under the crop canopy near solar noon on a calm, sunny day. Fields with optimum plant population will have very little sunlight hitting the soil surface, and also very few plants without ears.

Another consideration with regard to optimum plant population is yield potential. Many researchers have shown that the optimum plant population is greater under higher-yielding environments. For example, from 1991 to 1994 at four locations in Illinois, as yield potential increased from 135 to 225 bushels per acre, the optimum plant population increased from about 25,000 to 32,000 plants per acre. In other words, the optimum plant population increased by about 800 plants per acre for each 10 bushels per acre increase in yield potential.

In the last four years, there have been a total of 34 plant population comparisons conducted in 10 experiments at the University of Minnesota Research and Outreach Centers in Lamberton and Waseca. Averaged across all of these trials, yield was maximized at 36,000 plants per acre, and a final stand of 32,000 to 34,000 plants per acre was necessary to maximize economic return using current seed costs and grain prices. Additional information on corn production from the University of Minnesota is available on its new corn website: www.extension.umn.edu/corn.

Jeff Coulter is an agronomist with University of

Minnesota Extension

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