By Zachary Larson
Getting a corn crop off to a good start is a critical step in achieving good yields. Corn that emerges evenly without skips and doubles has the greatest chance for producing consistently sized ears on every plant, while those plants that emerge late relative to their neighbors will likely form smaller ears or none at all. Additionally, the plants adjacent to un-emerged or absent plants typically do not “make up” for the yield of the lost plant. More info on these concepts can be found in this Penn State Extension webpage .
Putting Emergence First
When considering upgrades, research suggests that your first dollar should be spent on the items that create consistent planting conditions. Those include row cleaners that create a residue-free zone which can warm and dry at a consistent rate. Row cleaners will also lessen instances where gauge wheels ride over rocks and larger residue, altering planting depth. Similarly, properly selected closing wheels will cover seeds without changing their location in the seed slot, avoiding emergence issues related to improperly covered seeds or seeds brought closer to the soil surface. There are many types of closing wheels (see Table 1); aside from standard solid wheels there are various spiked wheels, with and without depth limiting bands, and interlocking type wheels. When selecting closing wheels start with those commonly used in your area. If you’re considering a new design, try them on a few row units and see how they perform in your soils. However, be sure that you’re giving them the proper attention and making the right adjustments. Even the best of products will fail if not setup correctly. Also, be aware closing wheel performance can change based on soil moisture conditions, so trying new wheels in periods of extreme wet or dry conditions may not be representative of how they perform in “typical” settings.
Other products that can improve emergence include seed firmers that control seed bounce and seat the seed at the base of the seed slot. Actively managed downforce systems such as airbags or hydraulic systems also will promote consistent emergence by placing seeds at a consistent depth in the soil profile. While both systems can excel over a constant pressure system, hydraulic downforce systems respond to soil changes faster than air systems and may provide additional benefit in fields with lots of soil variability. Systems that adjust row cleaner depth and downforce can improve emergence as well. While they make it easier to perform the same adjustments that can be done manually, they can be a benefit in changing conditions or for those that manage large acreages, where time constraints or the inconvenience of manually adjusting row cleaners keeps it from being performed.
These interlocking-style closing wheels are one of the many types that can be found on the aftermarket. Photo Credit: Zach Larson, Penn State
A planter modification that has somewhat fallen out of favor are coulters. While initially targeted for slicing residue, loosening seed slots and reducing wear on opening disks, many farmers prefer the tradeoff of eliminating coulters in favor of maintaining sharp and properly sized opening disks and replacing them more often. Additionally, coulters can serve as a point of ground contact that holds a planter up, thus reducing the downforce on the row unit. Eliminating that point of contact can transfer more weight to the row unit, allowing it to penetrate firm soils easier than with the coulters on.
Metering and Precision Upgrades
Additionally, upgrades can be made to seed delivery and metering systems. This includes simple upgrades such replacement meters and more complex precision technologies such as variable-rate systems. New meters can reduce skips and doubles and decrease the variability of seed-to-seed spacing. In terms of return on investment, eliminating skips and the resulting loss in population will likely have the most impact followed by reducing the competition caused by doubles. The effect of even plant-to-plant spacing on yields appears to be more variable, with some studies demonstrating an increase in corn yield resulting from even “picket fence” stands and others showing no difference when compared to stands with more uneven spacing between plants. If your meters are causing lots of skips and doubles, investing in new ones may be warranted while upgrades to simply improve spacing may be less likely to yield a return.
While air bag systems can be used to dynamically react to changing soil conditions, hydraulic based systems have taken favor due to their increased responsiveness. Photo Credit: Zach Larson, Penn State
Innovations in seed tubes, specifically those that utilize a belt to place the seed in the seed slot are another means of improving spacing, and they’ve been emphasized as part of a system to enable faster planting speeds. While these seed tube designs will accurately deliver seeds to the slot at consistent spacings, chatter and bounce of the row unit will likely increase with greater planting speeds. Therefore, setups designed to increase planting speeds should be mated with responsive downforce systems and improved monitoring systems to ensure that good seed to soil contact is maintained.
Precision-focused upgrades include planter drive systems, with many moving towards row-unit mounted electric drives. These allow for individual row shutoff and variable rate population, while eliminating many mechanical linkages. Some of this functionality can be achieved with hydraulic drive systems and section or row-unit drive clutches as well. One advantage commonly seen with such setups is seed savings on end rows, point rows and overlaps. Savings claims are variable, but fields with odd shapes and short rows are likely to achieve greater savings than fields with longer rows and more uniform shapes.
Variable rate seeding is another place where drive system upgrades may have value, however that value is dependent on field variability and yield potential. A study from Ohio State and the University of Illinois considered a theoretical field comprised of sites of varying yield potentials, using seeding rates trials performed between 2012 and 2016 from across each state to represent the different yield zones. The Ohio sites revealed that corn had a quadratic response to seeding rates, which means that corn yields are lower when planted at populations below AND above the optimum rate. In that study, the economically optimum (most profitable) seeding rate ranged from 18,000 to 44,340 seeds/ac. with an average of 32,129. In comparison to using one theoretical uniform seeding rate of 32,721 seeds/ac. that averages all yield curves, the use of variable rates would have resulted in a return of $12 per acre, coming from both seed costs savings and increased yield. However, the savings from the Illinois locations were much lower at $3 per acre, as the corn yield response to population on average plateaued, meaning that there was little negative yield impact from seeding at too high of a rate.
The caveat to this study and the Ohio data in particular, is that the theoretical field was comprised from sites from all across the state. The variability within one field is likely much less. The Penn State Agronomy Guide’s estimates of optimum plant populations vary from 25,000 plants/ac. in lower yielding (<125 bu./ac.) environments to 35,000 in high yielding (>175 bu./ac.) environments, so there is still possibly for returns from variable rate seeding. In calculating whether a return variable rate seeding is likely, the marginal cost of implementing the practice should be considered. If the right precision equipment is already in place on the tractor and planter, the only cost may be creating a planting map. If you’re starting from scratch, there can be a significant cost in adding the necessary equipment, however variable rate may be one of many functions you may then have. If you are considering variable rate seeding Emerson Nafziger from the University of Illinois suggests to avoid creating seeding zones based on yield maps from years of low overall yields and to set your minimum populations assuming favorable weather so that you don’t lose upside when growing conditions are good. In addition, seeding zones derived from yield maps where there were agronomic issues for the year should also be avoided.
Like with many things in business, one eventually hits the point of diminishing returns. However, if the costs of upgrades can be weighed against those things that are known to give a return (focusing on even emergence) against those that may have more marginal gains (seed spacing) or require a more significant technological investment (prevision upgrades), you should have a good roadmap of where to start and how far to go.
Table 1: List of aftermarket spike and interlocking closing wheels
Source : psu.edu