I recall about fifteen years ago standing behind the barn with a farmer and being engaged in some agricultural small talk.  Looking over at his corn cribs, I asked him how many corn seeds he was planting per acre.  He told me his Dad planted most to the corn and that he liked to “drop” around 22,000 seeds per acre.  Before I could give him my patented 30,000 seeds/acre plant population oration, the young farmer continued that he had increased the seeding rate to 28,000 one time when his Dad was gone.  Expecting to hear positive results, the young farmer said, “Boy, I’ll never do that again!  The ears were too short and kept sliding through the holes in our corn crib.”  I figured discretion was needed at this point and simply changed the subject to Ronald Reagan’s “trickle down” economic theory.

        Well, times have changed.  Not too many 22,000 plants/acre fields exist anymore.  Several years ago, while doing many corn stand plant counts around the area, I found average plant stands to be just over 30,000 plants/acre.  This was true for both 30 and 36 inch row spacings and was right where we recommended final stands ought to be for maximum yield potential. 

        Recently, there has been a renewed interest in exploring the effects of plant populations well beyond the 30,000/acre mark.  This interest has been fueled by national corn growers’ contest winners who routinely plant 40,000 seeds per acre or more, an influx of several “maximum yield” programs, and improvements in corn genetics. 

        The push for maximum corn yields per acre can only be accomplished if plant densities begin to rise, even if it means giving up something in ear size.  Looking at the graph below, with above average grain weight and kernel number per ear, the BEST we can hope for at 30,000 plants/acre is a yield of about 180 to 200 bu/acre.  This maximum moves up to about 240 bu/acre at 35,000 plants per acre and 300 bu/A at 45,000 plants per acre.  (NOTE:  before you quit reading, the moral to this story will not be to plant 45,000 seeds per acre). 

       Okay, all of this is great theoretically but what about some “real” corn yields.  The next graph shows UW 2003 corn yields from 10 locations around Wisconsin with plant densities ranging from about 20,000 to over 50,000 plants per acre.  The solid line is the average of all locations and indicates maximum yields were obtained between 40,000 and 45,000 plants per acre.  Perhaps more importantly, the line slope is relatively steep between 30,000 and 35,000 plants acre.  Similar results were obtained in 2002. 

Corn Yield Response to Plant Density in WI in 2003 - Lauer, Wisconsin
 

        Of course final yield is not the only consideration in this story.  By now, most of you have already considered seed price.  Since 1990, corn seed prices have doubled from about $20 per acre to about $40.  Additionally, there is the lodging issue.  Make no mistake, a 40,000+ plants per acre stand will be much more subject to lodging where wind, insect damage, and stalk strength become issues.  What about drought?   Research from 1988 and the Marshfield and Chippewa locations in the above graph tells us that high populations won’t hurt yields during drought years but may not provide an additional advantage over lower populations. 

        I think the moral of this story may be to start experimenting between the 30,000 and 35,000 plants/acre final stand mark (especially if you’re in 30-inch or less row spacings).  At this level, the economics are still sound and there is little downside risk involved.  I plan to establish several plant density field plots around the county in 2004.  If you have an interest in being a part of this project, please give me a call at 929-3171.