MAKING AN EVALUATION
Corn Planting Performance
By Greg Stewart, OMAFRA Corn Specialist

Taking a close look at your corn fields this spring for yield-limiting conditions
will help with future equipment and management decisions.

When assessing your corn planters’ (operator and machine) performance this year, there are three specific things that you should look for: uniformity of plant spacing, uniformity of plant emergence, and consistency in obtaining desired final plant populations. Most of us appreciate the perfect “picket fence” field of corn, but it’s important to understand which elements of your corn plant stand contribute the most to your cropping profitability.

Uniformity of Spacing
Corn plants that are perfectly spaced down the row would seem to have a much better chance to optimize final yields. Equipment companies and agronomy researchers have contributed to producing more uniformly spaced corn fields and to promoting their necessity. Spacing uniformity can be measured by the occurrence of doubles or skips, or in terms of standard deviation. An absolutely perfect stand – where every plant is exactly 7.25 inches, (28,840 plants per acre in 30-inch rows) from its neighbour – would have a standard deviation of zero. If plants on average varied plus or minus two inches from the desired 7.25 inches then the standard deviation would be two. Dr. Bob Nielsen (Purdue University, Indiana) has conducted extensive investigations into the effects of plant spacing variability on final yield. He calculates that every additional one inch of standard deviation decreases yields by 2.5 bu/ac. When former University of Guelph professor Tony Vyn and I started narrow-row corn research in 1995, we went at it with the idea that plant-spacing uniformity might be less of an issue in 20-inch row corn due to the increasing ability for neighbouring rows to compensate for gaps. This research consisted of several different row widths, while imposing spacing uniformity differences by hand thinning shortly after emergence. Interestingly, this research has not shown any yield loss due to increased plant-spacing variability, regardless of row widths.

I have been concerned that the thinning operation might have been skewing the results by disturbing the neighbouring soil. So in 1999, we applied Roundup herbicide (via bingo daubers) to the plants that needed to be removed from the overplanted rows. The results were the same as in previous years: relatively poor plant-spacing uniformity yielded the same as the most precisely spaced plots. Earlier research at the University of Guelph by Vyn and Terry Daynard also indicated that differences in plant-spacing uniformity had little effect on final yields. Discrepancies between different research findings may have something to do with hybrids, plant populations, or other factors that confound spacing effects.

The point behind this discussion is not to encourage poor planter set-up, or ignore unevenly spaced corn, but to underline the following points:

• Don’t invest in a new planter simply to obtain picket-fence uniformity of plant spacing.
• If you have a modern, well-maintained corn planter and field conditions are suitable, the yield losses due to higher plant-spacing variability caused by faster planting speeds will be negligible and may be offset by corn-planting timeliness (see Table 1).
• Although not thoroughly field-tested, it appears that producers who operate air seeders for soybean and wheat planting with central metering and air delivery of the seed could also adapt this approach to corn planting, to increase efficiencies.

Uniformity of Emergence
Perhaps one of the most significant changes that you might consider making when evaluating corn planter performance is in looking at the uniformity of the plant emergence. Because it’s almost impossible to find time to actually monitor corn plants as they emerge, you will need to examine corn plant leaf numbers to see if the plants are all at the same stage of development. Some substantial research both in Ontario and in the U.S. Corn Belt has indicated that when neighbouring corn plants are not uniform in size yields will suffer. Dr. Emerson Nafziger (University of Illinois) has reported corn yields based on plots which have differences in uniformity of emergence (Table 2). These hand-planted plots consisted of uniformly planted plots on three separate dates. They also included various combinations of plots where certain fractions of the plants were planted later to simulate delayed emergence. In Table 2 you notice the treatment labeled 3E:1M consisted of one plant in every four being planted 10 days later than the neighbouring in-row plants. This resulted in a decrease in yield of 12 bushels (176 bu/ac) compared to the plots where all plants emerged uniformly on the early planting date (188 bu/ac).

When you walk your corn fields, keep the following ideas in mind:

• Plants that emerge late (so that they are two leaves behind neighbouring plants) will most certainly lower yields relative to the uniformly emerged stand, and may even lower it below those obtained by later-planted but uniformly emerged corn.
• Return on investment can be high for planter adjustments such as installing new opening discs, leveling the planter, properly adjusting seed firming wheels and proper seed depth placement.
• If field conditions are such that high planting speed and planter bounce causes one seed in four to be positioned out of moisture – and there is no rain for a week – expect significant yield decreases.

Plant Populations
The third element that should concern you is whether you actually have the desired final plant stand. Measure off 17.5 feet of row (30-inch rows) and count all the corn plants, multiply by 1,000 and you have the number of plants per acre. In Ontario, final plant populations should probably be 26,000 - 32,000 plants per acre. If your planter is not falling somewhere in this range, identify this as one of the first improvements to be made. If your plant stands are low, is it because you are not allowing for a 5-10 per cent reduction from seed drop to final stands? A recent research report published in the Agronomy Journal (D. Bullock et. al., 1998) indicated that the optimum final plant population in the midwest Corn Belt on average is 27,160 plants per acre. These researchers also predicted that for every 15 bu/ac increase in a field’s yield potential (or parts of fields), economically optimal populations increased by 450 plants per acre. So in Ontario, while we may generally shoot for slightly higher average final stands than in the midwest, you will also want to ensure that your productive fields are near the upper end of the plant population range. Fields that are traditionally lower yielding because of low water-holding capacity, poor soil structure, etc., have economic optimal populations lower in the range.

Keep in mind the following other points:

• Seed companies may provide you with additional information about the most suitable populations for specific hybrids.
• Researchers have shown that there is very little hope of a net economic return to investing in extensive site-specific soil and yield mapping and variable rate seed technology to adjust populations on-the-go.

So, when you are out enjoying your twilight stroll through your corn field this June, don’t forget to take along your clip board, pencil, calculator and yard stick!

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