on Friday, June 29, 2018
This week, I want to touch on Seed Spacing Coefficient of Variation (CoV). Most basically, CoV is a measurement of how much seed spacing varies. If a field is planted at 32,000 seeds per acre using a 30-inch planter, and if seeds were perfectly spaced, every seed in a row would be 6.534 inches apart. Two things affect Seed Spacing CoV: quantity of seeds in error (not spaced at 6.5 inches), and how far from 6.5 inches they are. The more amount of error there is, the higher the Seed Spacing CoV.
So why does Seed Spacing CoV matter? Corn is a plant that hates competition. Some plants respond well to competition, but corn loses yield quickly when it encounters too much competition. Normally we talk about what our ideal population is for a field or zone, however, we are actually referring to competition and seed spacing. Going back to this 32,000 population, if that is the ideal population for a particular field, then in reality we are just saying that in 30-inch rows, our ideal seed spacing is 6.5 inches to achieve the best amount of competition. Any deviation from 6.5” is going to lower yield. If we have a row that has a seed miss-placed we have too much competition on one side of the seed and not enough on the other, hurting us on both sides.
Skips and Doubles also affect CoV. Obviously, if our spacing should be 6.5 inches a double will create a 0 to 1 inch spacing, and a skip will create a 13-inch spacing. The effects of a double on yield, seem to be varied in studies, from some saying it will increase yield enough to make up for the cost of the seed, to others saying it will reduce yield but not as much as a skip. If the correct amount of competition is present (correct population) a skip will reduce yield almost assuredly. Corn seed does not germinate 100%, so we already are going to have skips due to seed characteristics. A planter leaving a skip will just add to this problem and reduce yield.
How much does Seed Spacing CoV affect yield? The actual yield loss due to CoV is hard to determine exactly. Many factors affect this. If population is higher or lower than the ideal, it may increase or minimize the impacts of inconsistent seed spacing. Furthermore, other factors come into play, like emergence and variety. Part of the goal of our testing is to be able to determine yield differences across whole fields, against several different types of planters, with several different types of seed. Once we finish compiling all the yield data, we will have a better idea how the planters preform against each other in terms of yield.
Hands down, the ExactEmerge outperformed other planters in Seed Spacing. We are seeing Seed Spacing CoV values around 20%-30% lower with the ExactEmerge as compared to the planters we ran it beside. I believe I should have had the ExactEmerge adjusted a little different eliminating more doubles, further improving seed spacing. When walking through the field the difference in seed spacing is noticeable, there’s no need to look on a map to see what planter was used.
Below are some good articles on plant singulation: