Scratch head over speed of planting results

The slowest planting speed of 4 miles per hour produced the best stand placement in the Indiana Prairie Farmer/Precision Planting trial at Purdue’s Throckmorton Research Center. The distance between plants in one-one-thousandth of an acre was measured in each plot. From those numbers, Jeff Phillips, Tippecanoe County Extension ag educator, calculated the standard deviation. It’s a measure used to determine how much a stand varies from an ideal stand. The smaller the number, the more uniform the spacing.

Key Points

A planting speed of 4 miles per hour produced excellent spacing.

Driving 6 miles per hour still produced respectable plant spacing.

However, the yield results can be difficult to explain.

The stand planted at 4 mph was significantly more evenly spaced than that at 5 mph, which was significantly better than the one planted at 6 mph. That’s not unexpected. Until harvest, the trial seemed to reaffirm that slower planting speeds pay. After the combine went through, Phillips and Dave Nanda, director of genetics and technology with Seed Consultants Inc., were scratching their heads. The 4-mph plots yielded the least, with the other two nearly identical. None of the yields were statistically different, meaning the difference could be due to chance or experimental error.

Examine standard deviations

Bob Nielsen, Purdue corn specialist, emphasized the importance of accurate seed drop and even spacing 20 years ago. His plots showed that for each 1 inch increase in standard deviation, such as from 2.0 to 3.0 inches, yield could be hurt by 2.5 bushels per acre.

“You shoot for zero standard deviation, but Nielsen says 2.0 is good,” Phillips notes. “Although we had differences, all of them were very respectable, from 1.97 for 4 miles per hour to 2.46 for 6 miles per hour.

“Planters are more accurate today,” he says. “And people pay more attention to planter maintenance and correct settings. With the differences we saw, we wouldn’t expect much yield advantage.”

Another view

That still doesn’t explain why planting at 4 mph yielded less, even though it wasn’t significant. Nanda noticed an increase in population at 4 mph. With the plot planted May 27, pollinating and maturing took place under very hot, dry conditions, and it may not have been the year to have extra plants, he notes.

Nanda is a firm believer in maximizing plant populations to fit soil types. However, he also believes that you can plant too thick if the soil type can’t support it, or if unusually hot, dry conditions develop. He’s learned that lesson working with gravelly soils, with and without irrigation. In those situations, the difference can be striking.

To be fair, speed of planting wasn’t the only factor where average number of plants varied from one factor to the next. Yet in some cases, thicker plots actually yielded more.

Still, Nanda believes strongly in planting at moderate speeds. He still thinks it’s an important factor to achieving a good stand that’s evenly spaced.

“You want to give equal opportunity to each plant to get water, sunlight and nutrients,” he concludes.


Ready, set, go: Pete Illingworth of the Throckmorton Research Center farm crew prepares to jack up the throttle and head into this plot at 6 mph. Stands weren’t as evenly spaced, but yields were just as good as plots planted at slower speeds.

This article published in the February, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.