Corn Planting Considerations
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.