Crops: The Lynch File - Do you know what your corn population really is?

Thursday, June 10, 2010

You may know how many seeds you dropped, but have you done a population count on your stand? You might be surprised at what you find

by Pat Lynch

What is your corn population? Not what you dropped, but what you have now. You probably know how many seeds you dropped, but how is your stand? Your final population says a lot about your corn planter. If you are concerned, why not go now and do a population count?

There are lots of books to tell you how to measure 1/1,000 of an acre. This is the standard for doing a population check. Check at least four rows everywhere you do a stand count. Check various places in the field. Check good ground and poor ground.

Check the number of doubles. Doubles or triples are when two or more seeds are growing one to two inches apart. Doubles cost you about $2.50 per acre in extra seed cost.

Check for uniformity of stage. There has been much discussion over many years about uniformity of stand. One thought is that "you need uniform plant spacing for top yield." The opposing point of view is that "if you have the right population, the spacing between plants is not critical." I agree with this latter opinion.

However, often when there are gaps and uneven spaces in stands, there is also a difference in stage of development. I believe this difference in stage is more critical to final yield than the spaces between plants. It is not uncommon to have plants in 1/1,000 of an acre that are one leaf apart, say at the five to six or six to seven leaf stage. If you have plants that are two or three leaves apart, this will affect yield. Figure out why there is this difference.

The most common causes of different stages are poor seedbed and uneven depth of planting. Check the depth of seed. It should be uniformly 1 ¼ to 1 ½ inches deep. If it is poor seedbed, figure out changes for next year. If it is uneven emergence due to seed depth, figure it out.

If you have plots, check the population now in those plots. You want to be sure you are measuring what you think you are measuring and not a difference in population. It is interesting that, in the fall, all hybrid comparison plots indicate that all hybrids have the same population. These populations are all indicated as being the same as seed drop. From my experience, you never get the same population as seed drop.

There is always a difference in populations among hybrids. Would you give credibility to hybrid comparisons if you knew that one hybrid had 2,000-3,000 more plants than the hybrid beside it? Maybe you would. Maybe that is a characteristic of that hybrid's ability to emerge. If you know there is a difference in population, you can take that into account when deciding what hybrid you should grow next year, based on performance this year.

And if you found some surprises in your corn populations, you should go and find out what your soybean populations indicate about how they were planted. Check the variation from row to row and area to area. The variation you find there will be even more astounding. BF

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