Crop Comments: Successfully Planting Lower Corn Populations

Awhile ago, my friend Tom Kilcer (a certified crop advisor, whose wisdom I seek frequently) was giving a lecture at a Midwest crop growers’ conference. He explained how corn populations can be reduced without hurting yields – in fact, possibly increasing yields, if plant crowding had been an issue.

After the lecture, a grumpy attendee (a seed salesman) chewed Tom out royally, due to the threat of reduced seed sales.

How crowding affects animals is something I learned before acquiring a knowledge of how excessive population affects plants. Most of us are familiar with the adverse effects of overcrowding on livestock. But it may be difficult to compare too many hoofed animals crammed into too small a space to plant overpopulation. However, comparing certain fish to crops is quite a bit easier.

Tilapia were originally farmed in their native Africa. Fast-growing, tolerant of stocking density and adaptable, tilapia have been introduced to many venues to be farmed extensively. Most folks are more familiar with goldfish than they are with tilapia.

Goldfish in an indoor aquarium that start as two inches long might grow to be three inches long. Those same fish in a small backyard pond will likely grow to be a foot long. If they escape into a much larger habitat, like a lake, we call them carp. They can grow to two feet long, weighing up to 8 lbs. (although carp occasionally weigh in the 30- to 40-lb. range). The size of the environment of the goldfish has everything to do with how much it can grow.

But let’s return to tilapia. These were grown at the Milford vocational school (where I advised the ag program 15-plus years ago). Tilapia addressed their restrictive environment by limiting their body size. A volume of water that might have enough room and nutrition to support 100 big fish could support 200 smaller fish.

Tilapia are vegetarians, so big ones don’t eat little ones. Game fish (like pike and bass) approach the crowding issue a little differently; big ones do eat little ones.

Now let’s compare the versatility of these fish to the adaptability of corn and sorghum (and sudangrass).

These plants are all in the C-4 grouping. C-4s use building block modules consisting of four carbons. What’s special about this trait is that it enables C-4s to acquire – and utilize – carbon dioxide and water more efficiently than plants that are not C-4s. Over the last 60 years or so, growers have quietly been convinced (by seed marketers) of the need to plant higher numbers of seeds of sorghum, sudangrass (its hybrids) and corn.

Flashing back to my Cooperative Extension days as an agronomy agent (in the 1970s), Cornell 110 was a much better than average corn hybrid. Its 80,000 units did a good job planting three acres. Thirty-six-inch row spacing was popular; 90% “germ” meant a final stand population of about 24,000. We agents were told that if half of that population was lost, but that the remaining stand was uniform, there was no need to replant. The surviving plants “ate” the nutrients their fallen buddies no longer could.

I remember a case in the 1970s when an Otsego County dairyman called me to examine a piece of corn with major problems. He had planted it early, and then it got frosted. Thinking it was all dead, he replanted.

However, the first planting actually survived. So what I was examining was roughly a 60,000/acre population, which was very yellow. Extreme crowding meant there wasn’t enough nitrogen for all the seedlings.

Additionally, the original population fought the newcomers through a behavioral trait called allelopathy. This is a biological phenomenon wherein one plant inhibits the growth of another, using its own perfectly natural biochemicals – similar to what fish do to lesser comrades. What the farmer ended up harvesting was about three-quarters of the normal whole plant dry matter per acre that was poorly eared. Had he called me before he replanted, I would have been able to determine that the seedlings’ growth points were still slightly below the soil’s surface, thus fairly protected from frost, despite the fact that the first true leaves were quite withered. He would not have had to replant.

Let me tap into the expertise of Wisconsin crop advisor Daniel Olson, who oversees a crop consulting firm called Forage Innovations. He does sell seed, but he tries not to sell growers more than they need. Olson wrote about a physical corn trait called “maximum ear flex.” It’s a necessary characteristic for BTBMR (better than brown midrib) corn, enabling it to provide the bushels of corn equal to or greater than the higher planting populations, often with two ears per stalk occurring. Many hybrids have ear flex, but they must also exhibit adequate stalk expansion so as to enhance both yield and digestibility.

When the stalk expands, the lignin (only the outer rind) becomes a lower percentage of the neutral detergent fiber (NDF). At the same time, the highly digestible center – mostly hemicellulose, cellulose and sugar – becomes a greater percentage of the whole plant. I compare this to silo diameters. As a silo gets a wider diameter, the silage capacity increases in a non-linear fashion. When lignin, the portion of feed remaining undigested after 240 hours, is reduced as a percentage of NDF, digestibility increases.

The punchline to the joke here, so to speak, according to Olson, is that with BTBMR the kernel numbers of seed corn that used to plant three acres now plants four acres. That’s good news for corn producers, but it also applies to folks growing sorghum, sudangrass and their hybrids. Seed sales reps may not consider it good news – like the salesman who verbally attacked my friend Tom a few years ago. Because this management approach tends to reduce seed sales.

by Paris Reidhead