Why corn populations are going up

Wednesday, February 2, 2011

Seed companies say high-yielding environments warrant higher populations. But you need to factorin the extra seed costs

by PAT LYNCH

The price of corn is not the only thing that has gone up recently. Corn populations have also done so. Corn prices may not stay high, but corn populations probably will.

This trend to higher populations is being led by corn companies. On the one hand, they have the results to show where you should use higher populations. On the other, they are not promoting it as aggressively as they should. They feel that growers will not accept this information. They fear growers will think it is just another way to sell more seed.

I have looked at it from different perspectives and I will share the information that I have to encourage growers to look at seeding higher populations.

Information from Dekalb indicates that, as you increase populations, you can increase yields. Dekalb has looked at populations and yields over four years. Its information shows a 7.6 bushel per acre yield increase by planting 35,000 seeds per acre versus 30,000 seeds per acre in high yield environments. It also shows that, if you increase populations to 35,000 seeds per acre and the yield environment is less than 160 bushels per acre, yield can actually decrease. It is the high-yielding environments that warrant higher populations.

Information from Pioneer on its hybrids also suggests that growers should be planting more than 30,000 seeds per acre. Pioneer has developed population response curves for its main hybrids. Its information suggests that not all hybrids have the same response curve. Some hybrids will top at a 32,000-seed drop while other hybrids show a yield increase up to 36,000 seeds per acre.

If you are looking at increasing your seed drop, you need to factor in the seed costs. Some of the newer genetics cost about $2.50 to $2.75 per thousand seeds. By increasing your seed drop by 5,000 seeds per acre, you increase costs by $10-14 per acre.

Are the triple-stacked hybrids more population responsive? DeKalb's information suggests that they are.

The Ontario Corn Hybrid Trials are grown at 30,000 plants per acre. Most of these plots are over-planted and hand-thinned. I am told that the Ontario Corn Committee will look at increasing the populations for 2011 planting. This may help sort out population-responsive hybrids.

When you over-plant and thin, you tend to thin out poorer plants. I refer to these plants as runts. Growers do not have this luxury. This may be why there is a population response in some grower fields. If a percentage of plants do not get off to a good start, then having more plants compensates.

The most obvious reason for poor plant establishment is related to seed bed. Not every inch of soil is worked as well as it could be. If you have poor soil conditions resulting in poor emergence, the later emerging plants will never catch up. Having more good plants will compensate for these weaker plants.

I have often wondered if some of these runt plants are in the bag when you plant them. Many other species commonly have runts. The term runt of the litter is based on fact. To have corn seed grow runts is not a stress.

Some fields show a response because of an improperly set planter. Too often growers drop too many doubles. (A double is when two seeds are so close together they are acting like one plant.) It is hard to drop less than 1,000 doubles per acre. If you are dropping 2,000-3,000 doubles per acre, two things happen. First, you are dropping $3-$5 of seed per acre that is not returning anything. Second, if you did a population trial on your farm, it would probably show a response to a higher population. This is because of too many runt plants.

I have seen many fields where there is a big difference in the ear size of plants that should all have the same size ear. Is this genetic or man-caused? Whatever the cause, planting more seeds per acre will compensate. Or it just may be that the newer genetics respond to higher populations. BF

Consulting agronomist Pat Lynch, CCA (ON), formerly worked with the Ontario agriculture ministry and with Cargill.