Seeding Depth Affects Corn Plant Emergence Uniformity and Grain Yield
Rarely do we see a paper published on corn seeding depth and the subsequent impact on grain yield. Precision technologies have allowed for capabilities of variable rate seeding, multi-hybrid planting on the go, and the ability to vary planting depth in real time in response to real-time soil moisture data. In a paper published by Nemergut et al. (2021), corn seed was planted at 1-, 2-, and 3-inch depths on two soil types in Ohio over three growing season (2017 to 2019). Shallow planting resulted in less uniform more extended emergence periods than 2- and 3-inch planting depths. If a plant emerged within 3 days of the first emerged neighboring plants, then there was no effect on plant grain yield. Any plant that emerged more than 3 days after the first emerged plant had a 5% decrease in kernel weight per day. Grain yield per plant increased as planting depth increased. Grain yield per acre was significantly increased by planting depth with seed planted at 2- and 3-inches yielding 8 or 10% more than the 1-inch seeding depth on one of the two soils. Other researchers have also shown improving emergence uniformity can positively increase yield, and that optimum planting depth may vary by field.
Further Reading
Nemergut KT, Thomison PR, Carter PR, Lindsey AJ. Planting depth affects corn emergence, growth and development, and yield. Agronomy Journal. 2021;113:3351–3360. https://doi.org/10.1002/agj2.2070
Edge of Field Syndrome in Corn: Reality or Myth?
Over the past five years or so, we have been hearing stories about fields of corn that show serious yield losses on the edge of the field, specifically on the South and West sides of corn fields, with yields as much as 50 bpa off the rest of the field. I have personally seen yield maps that suggest that this is a reality but explanations have been speculative at best.
Researchers at Iowa State and other universities have alluded to several scenarios that may help explain part of the yield deficiency but several cumulative environmental factors are the most likely culprit. Below are several potential explanations for this relatively new phenomena.
Herbicide drift. In the current ag climate, herbicide drift seems to get the blame for every visible issue we hear about in the country, especially as it pertains to dicamba. We recognize that poor timing of herbicide applications in corn can cause major yield losses. For instance, when Roundup is applied to corn at silking, this can cause roughly 25% of the kernels to abort. This phenomena has also been observed when aerial applications of fungicides with non-ionic surfactants also killed kernels. Could other herbicides be causing stress that lowers yield as well?
Differences in transpiration on the field edge. During the growing season, the middle of corn fields tend to be cooler due to better shading of the ground and higher plant density. As these corn plants respire water, it provides a cooling effect within the field. The edges of the field, however, are less dense and more prone to air movement through the canopy, which diminishes this cooling compared to the middle of the field. We see the same effect in the fall, as corn on the edge of the field is drier at harvest than the middle. Could dry wind blowing at the edges of fields be limiting yield due to more moisture stress as plants try to cool themselves?
Poor fertilizer applications. I have unfortunately witnessed several instances where custom applicators do not get fertilizer spread completely to the edge of the field. This may be due to wind at time of application or just poor management by the operator. A single year of poor fertilizer application would not necessarily show diminished yields in that cropping year. Estimates show that only 36-45% of our fertilizer applied is utilized by the crop in that year but one can envision how several years of poor fertilizer applications would have a negative effect at the edges of corn fields.
West edges historically yield worse. In fields planted in strips of alternating corn and beans throughout a field, growers have seen overall better corn yields than a solid field of corn. Data from the Northeast Iowa research farm have shown when individual rows are measured in these corn strips, the yield of the Eastern most row is substantially higher than the West row in a North/South planting orientation. Over 10 years of research, the bushel difference is a little more than 26 bpa! In these strips, the outside rows generally yield more than the inner rows, to the tune of roughly 90-100 bushel more, with exceptions occurring under severe stress as we saw in 2012 when outside rows have yielded less. Could the West edge of a field just naturally yield less?
In summary, if you are experiencing what you feel are edge of field yield losses, I would consider the potential issues above and suggest a few basic steps to eliminate each as a suspect. First, take a soil sample from the edge of the field where losses are occurring and compare those results to the middle of the field. Secondly, keep track of accumulated heat units as a guide for the growing year; extremely hot and dry conditions will lower yields but, under extreme heat and dry weather, the edge of the field may be hurt worse. This has been the case in Iowa the last 2 years. Finally, be very careful not to spray adjacent fields when your corn is tasseling to avoid stress at that pollination.
2021: Ear Slippage a Concern – No Ifs, Ands or “Butts”
July is the pivotal month for corn growing, as growers and seed specialists like myself spend hours watching the highs and lows of each day, hoping to keep the highs below the 86 degree threshold while getting lows below 70 at night to give those corn plants a break. In cases of readily available moisture, these concerns are often not a major issue, but in much of the corn belt in 2021, drought stress has given much cause for concern for our fall harvest.
What are some of these concerns? First, in a lot of dry areas, the amount of corn rootworm beetle pressure is immense. I have been actively trapping beetles since the middle of July and some of the fields are showing an average of 43 beetles caught per plant per day! That is roughly 20 times the economic threshold. These numbers are downright scary thinking about the number eggs that these adults are laying and will be resulting in root-feeding larvae next year. Another threat potentially related to this drought stress and excessive rootworm pressure has me equally concerned for this year’s crop; poor kernel development at the butt of the ears.
Many of you who have been in the seed business for some time have encountered “ear slippage” in the fall. The bulk of the time, growers immediately want to blame the hybrid for their ears lying on the ground, but that is just not the case. One contributing factor to this is drought stress. The shank and ear are anatomically similar to the stalk above the ear attachment. Therefore, it is no surprise that if that portion the stalk is fragile from drought stress, so will be the shank. This year, another stress related cause of possible ear slippage is simply poor pollination of the butt of the ear. Note the arrowed areas of the picture below: overall the ears look filled out fairly well, but the kernel spacing around the butt is irregular. This causes those kernels to grow quite large and wildly out of place. Ultimately they push the ear away from the shank attachment. The result is ear slippage.
In addition to severe heat and extended drought at this stage of ear development, other factors can influence pollination. These include improper applications of some herbicides, insect feeding on early emerged silks that pollinate these first ovules, as well as poor fertility. Heat stress is usually the major culprit alone, or in conjunction with these other influences.
So what can be done if this is a potential problem? I would strongly encourage growers to spend some time this fall gauging whether or not this could be an issue as well as looking at general stalk quality and then prioritizing those fields for earlier harvest. There is really no solution other than harvesting while the ears are still intact. So check out your fields and put together a harvest plan, or you might feel the pain of ear slippage.