Corn Planting Considerations
By Greg Stewart, OMAFRA Corn Specialist

It's not too early to start thinking about corn planting, especially if your present planter needs to be fixed or overhauled or if you are considering making some purchases to modify or replace existing equipment. When considering the performance you obtained from your corn planter last year and what you hope to be able to do this coming season, consider these factors: planting depth, uniformity of emergence and uniformity of spacing.

Planting Depth
In the last couple of years there has been considerable discussion about corn planting depth with the aim of promoting deeper corn planting. One of the main arguments made in favour of planting deeper is that the growing point and first nodal roots are more favourably positioned (deeper), preventing both rootless corn and herbicide injury to the growing point. These considerations are both valid when taken in the proper context. That is, some soil-applied herbicides require planting depths of at least 1.5 inches to prevent growing point damage. And some seedbeds which are coarser and drier at the surface will be more prone to poor root establishment in shallow plantings. Warmer, drier springs such as the one we experienced in 1998 lend themselves to successful deeper corn planting. In fact, many of the corn emergence problems from last year stemmed from corn planted too shallow in soils that were already too dry to cause germination. When rainfall did not come within five- to 10 days of planting, emergence suffered. For that optimum corn emergence producers should get off the tractor to check that seeds are firmly placed in moisture, regardless of the depth they think the planter is set at.

The suggestions that planting at 2.25 inches would result in significantly larger ears and higher yields than planting at shallower depths has been somewhat disturbing. Does this deeper is better approach always pay dividends? Research at the University of Minnesota done by S.C. Gupta showed that under cool soil conditions, planting deeper can cause significant emergence delays. This research indicates that under warm soil conditions (15-25 degrees C) planting corn at one, two, or three inches deep had little effect on emergence rates, but under cool conditions (5-15 degrees C) the deeper corn-planting depths caused significant delays in emergence.

In conditions where soil temperatures are lower (i.e., early season, cool season, no-till, etc.) and when soil moisture levels are adequate, producers should consider that shallower planting (1-1.5 inches) is warranted. At these depths the germination process generally compensates and assures suitable positioning of the growing point and nodal roots. As for being too shallow for protection from herbicides, producers should consider that corn being planted shallow to alleviate some cold temperature stress would be better off left to emerge without the additional stress of soil applied, pre-emerge herbicides.

Uniformity of Emergence
At whatever depth you decide to plant, it's important you do all you can to assure uniform germination and emergence. Dr. M. Tollenaar of the Department of Plant Agriculture, University of Guelph conducted studies in 1998 which pointed out that corn plants which emerge 3-4 days behind their in-row neighbours may be significantly disadvantaged in terms of competition for sunlight and in grain production. Careful planter preparation may be the single biggest factor in getting uniform emergence. Check to see that the planter is operating level and that all discs, depth gauging wheels and seed firming devices are aligned and up to specifications. Pre-planting management may also play a critical role in emergence uniformity. If the field is left too rough, if residue is bunched, or if surface compaction has not been uniformly alleviated, you may be asking more than even the most carefully prepared corn planter can deliver.

When you assess the job your corn planter has done this spring (after the corn is up) pay attention to overall plant population and plant spacing and be sure to examine corn plants to see if they are all at the same leaf stage. If you can find plants that are one or two leaves behind their neighbours it could be an indication of potential yield loss and something you will want to remedy for the following season.

Uniformity of Spacing
I rank proper depth of planting, uniformity of emergence, and correct overall plant population as being more important than uniformity of plant spacing. Work done at the University of Guelph has found that at relatively high populations (28,000 - 36,000 plants per acre) plots with less uniform corn plant spacing have generally not yielded lower than plots with more precise plant spacing. For most producers that are upgrading or repairing their corn planters to ensure depth control, even emergence and accurate populations, improved spacing will be a natural part of the package.

Some producers are including air seeders and/or drills along with narrow rows or twin rows as part of their corn planting system and are prepared to live with more plant spacing variability. It's important to note that even in these systems where uniformity of spacing may be sacrificed, the precision requirements for seed/soil contact, depth control and plant populations are the same as with more conventional corn planting equipment.

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