How Thick Should I Plant my Corn?

Increasing populations of corn grain and silage seeding rates have dramatically risen in recent years.

I was recently searching my files looking for an old, hard copy of a reference article. Since the advent of computers and Google, I find I use filing cabinets less frequently. Anyway, I came across an article printed way back in April 1997 by Dr. Joe Lauer, University of Wisconsin, entitled “How Thick Should I Plant My Corn?” Increasing populations of corn grain and silage seeding rates have dramatically risen in recent years. Reports from recent PA Five Acre Corn Grower Clubs show that today most top corn yields are from fields with average, at harvest, plant populations/acre of 31,000 to 32,000. I was curious how recommendations have changed so I glanced through the fact sheet.

In 1997 Dr. Lauer reported results from population studies from 1994–96 looking at planting rates of 18,000 to 42,000 seeds per acre. The agronomists noted that high populations can result in greater lodging, poorly filled ear tips and a greater number of barren ears. The ideal plant population for any particular field depends on many factors including: soil type, planting date, hybrid, soil fertility and moisture. In this 1997 study optimum population for silage production was at 30,000 plants per acre (at harvest).

I easily did a Google search for Dr. Lauer at UW and corn plant populations and found an article he wrote in April of 2009. In that article he reports on population studies conducted from 2000 to 2008. In these studies the plant population (density) at harvest was 20,000, 32,000, 38,000, 44,000 and 50,000 plants per acre (ppa). In this study they measured grain and forage yields. Maximum grain yield was at 38,000 ppa and maximum Milk per Acre yield was at 41,000 ppa.

Across all dairy and grain production areas there is sufficient on farm research that shows an advantage to increasing corn plant populations at harvest. Not all areas or even fields are capable of growing a corn crop at these high levels but plant population trends are definitely increasing. The range of populations for optimizing corn silage production in PA is 28,000 to 32,000 plants per acre. Note that this is total number of plants, at harvest. What were your population numbers, at harvest?

At some population levels and 30 inch rows there may be limited space within the row to develop a crop. At that time the shift will go to narrower row spacing. As equipment becomes more available the adoption of 15 inch row corn silage production will probably become more common. Being able to space out plants more evenly across an acre of ground will provide additional room to grow for each ear. The total number of ear bearing stalks per acre is what drives yields. Narrower rows will allow an increase in total population at a more equal spacing.

Dr. Lauer makes an excellent agronomic recommendation. He notes that by adjusting plant populations, grain and silage growers can change current yield levels. He recommends growers look to increase their populations on a small scale by planting some fields at what is considered the optimum plant density and then make 2 or 3 rounds with a 10% increase in seeding rate within the same field. Yields can be monitored at harvest and adjustments made the following spring.

Where will populations be in the next 12 years? And, will I still even use a filing cabinet?