For the past couple of growing seasons we’ve been conducting studies on emergence. Emergence is often touted as one of the hallmarks of optimum yield. We hear it from the big yield record holders like David Hula and Randy Dowdy: uniform emergence is important for maximizing yield. Randy Dowdy’s goal? Get all the plants up on the same day. The more uniform emergence, the higher yield potential you will have for that field. The adage states that a plant that emerges 48 hours after its neighbor would be considered a weed and that for maximum yield potential, all plants should be up within 48 hours of each other. So how true is this statement? Is there too much stock placed in getting everything up in 24 or 48 hours? Or does it have as big of an impact as assumed? This article will address those topics as well as our own findings in the 2017 emergence studies.
A variety of studies have been conducted regarding emergence. Many of these studies are geared towards a two leaf or greater difference in emergence. In once study, adjacent plants with more than two leaves difference in growth stage resulted in no ear set on the smaller plants. (Nielsen, 1993) Liu et al. found that 1/6th of plants with a two leaf delay reduced yield by 4% and 1/6 plants while a 4 leaf delay reduced yield by 8%. If a plant was next to a “delayed emerger” the plant did not compensate as it would if next to a gap. (Liu, Tollenaar, Stewart, & Deen, 2004) A wide range of studies suggest that emergence delays result in a 5-9% yield loss. However, a two leaf difference in maturity would be equal to around a 10 day difference in emergence. Many times in our fields we are looking at a window of 3-4 days for emergence, not 10 days. So what impact does a 3-4 day window have on yield?
A study by Pioneer Agronomists outlined some effects of uniform emergence for a shorter time-frame. Plants emerging evenly will put on one similarly sized ear. Those varying in emergence will likely not put on a full sized ear. However, the study from Pioneer found that while yield can be reduced at that point, even those that had delayed emergence beyond 48 hours were not considered “a weed” and did contribute to overall yield.
We were curious about what these studies had found and wanted to do some tests ourselves. Every 12 hours emergence was assessed at 1/1000th of an acre at 3 field sites. Plants were flagged starting when we saw the first plant spike through. Plants were assessed 12 hours later and flagged with a different color. This was repeated every 12 hours until all plants in that row were up. At harvest time, ears were harvested and grouped by emergence date. Yield was calculated based on ear weight.
So, what did we find? In 2017, we found that 74% of yield was attributed to plants that emerged within the first 24 hours of each other. This was mainly due to the fact between 65-86% of plants emerged within those first 24 hours. So, what if we looked at it by individual ear? Ear size was generally a little larger during the first 24 hours and outweighed later ears by 1-2.5 oz per ear. That translates to 0.6 to 1.7 bushel per plant difference in the first 24 hours versus second 24 hours. It’s important to note that plants emerging after 24 hours still contributed to yield, although to a slightly lesser degree.
What if all plants that emerged from 24 to 48 hours had the average ear size of the plants emerged in the first 24 hours? In the case of the first field site, that would result in an overall yield of 187. 5 bushels per acre, compared to the actual measured yield of 184 bushels per acre. In the second study site, a uniform ear weight would have resulted in a yield of 77.8 bushels per acre, versus the actual 73 bushel per acre. Finally, in the third study, uniform ear weights would have resulted in 178.32 bushels per acre verses the actual 171.5 bushels per acre. In these cases, emergence that took place from 24- 48 hours resulted in a 2-6% yield reduction compared to what optimum yield could have been if all plants had emerged in the first 24 hours. Each plant that emerged from 24-48 hours was still a contributor to overall yield.
So what did we learn from our 2017 study? While plants that emerged between 24 and 48 hours yielded slightly less than their 0-24 hour counterparts, they still contributed to total yield. Overall, emergence within the first 48 hours resulted in similar yield performance by plant, with yield slightly higher in the first 24 hours. We are limited in this study to just three sites and by the window of emergence. Only site 2 had any plants emerge outside the 48 hour window, with just 2 plants emerging between 48-60 hours. The yield of the two plants emerging in the 48-60 hour window were 1 bushel per plant less than those emerging in the first 24 hours. Because we were limited by the emergence window, we could not test the effects of emergence past 48 hours. More data is needed to test the 24 to 48 hour threshold. We are limited by the conclusions we can draw from this study due to the previously mentioned limits on locations and emergence window as well as impacts of weather on yield and planting conditions.
Several more emergence studies were implemented during the 2018 growing season. Some locations had all plants emerge within 24 hours, and some locations didn’t show complete emergence for 6 days. This variety of plant emergence should provide a good framework for some practical testing of emergence beyond the 48 hour mark. We will post results from the 2018 growing season come harvest time.
How do we get uniform emergence? The major component of uniform emergence is planting depth. If plants are placed at the same depth, there is a greater chance of all of the seeds coming up at the same time. Seeding depth is affected by planter speed, down pressure and guage wheel settings and field conditions. An article from Ohio Country Journal reminds readers that seed tubes and planter units are designed for accuracy at certain speeds. Increasing above those speeds will decrease accuracy of seed depth and placement. (“Uniform corn emergence tips| Ohio’s Country Journal,” n.d.) Taking time to correctly set the planter may have a 2-4% impact on yield due to improved emergence.
Have any of you tested this on your own fields? What did you find? Comment below with some of your results or questions about the study.
Liu, W., Tollenaar, M., Stewart, G., & Deen, W. (2004). Response of Corn Grain Yield to Spatial and Temporal Variability in Emergence. Crop Science, 44(3), 847–854. https://doi.org/10.2135/cropsci2004.8470
Nielsen, R. (1993). Stand establishment variability in corn.
Planting Outcome Effects on Corn Yield. (n.d.). Retrieved June 5, 2018, from https://www.pioneer.com/home/site/us/agronomy/planting-outcome-effects/
Uniform corn emergence tips| Ohio’s Country Journal. (n.d.). Retrieved June 5, 2018, from http://ocj.com/2017/02/uniform-corn-emergence-tips/
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