What Uneven Corn Spacing Costs You Per Acre
Purdue measured it. About 2.5 bushels an acre for every inch of spacing variation, and most fields it checked had room to gain 5 to 7.5.
Purdue's Bob Nielsen spent years measuring plant-to-plant spacing in real fields. His numbers are worth knowing, because they put a price on something you can't see from the road.
The numbers
- In field trials across Indiana from 1987 to 1993, yield dropped about 2.5 bushels an acre for every 1 inch increase in the standard deviation of plant spacing.
- In a 2004 Purdue trial, the same measure cost about 2.2 bushels an acre per inch. The most even plots made 192.4 bushels. The least even made 178.5.
- Across more than 350 commercial fields in Indiana and Ohio, only about 16% of fields came in at 3 inches or less. About 60% were between 4 and 5 inches, and about 24% were at 6 inches or worse.
Nielsen's target is about 2 inches, not zero, because some seed never comes up no matter what the planter does. By his math, the 60% of fields at 4 to 5 inches could gain 5 to 7.5 bushels an acre just by getting to 2.
Put that on your own farm. At $4 corn on 1,000 acres, 5 bushels is $20,000 a year.
The newer number
Precision Planting ran its own 5-year study from 2018 to 2022, on vSet plates rigged with plugged and extra holes to force skips and doubles. Meters at 95% singulation against 99.5% lost $41 an acre, or about 2.1 bushels an acre for every point of singulation. It's the maker's own study, so weigh it that way. But singulation is a number you can read on your 20|20 today.
What to keep in mind
That field survey is decades old, and today's meters are better than what was running then. But a worn meter isn't a new meter. Other researchers have found losses from about 1.5 bushels per inch up to 3.4, and a couple of studies found almost none. So treat this as a yardstick, not a promise.
What causes it
Purdue lists the usual suspects: wrong air pressure, leaks, worn knockoff brushes, and the wrong disc on air planters. On finger meters, worn fingers and bad tension. Then there's speed, and tired seed belts.
Most of that can be found on a test stand in the off-season, which beats finding it on your yield map.
Check your own field
You don't need anything fancy. In a few spots in the field, measure the inches between plants down 30 feet of row. Put the numbers in a spreadsheet and use =STDEV. Over 3 inches and there's money to go find.
Sources: Purdue, Stand Establishment Variability in Corn, Purdue, Effects of Uneven Plant Spacing on Corn Grain Yield and Precision Planting, Should I Calibrate My Seed Meters?.