Shallow Planting Depth Doesn't Always Means Corn Comes Up First

Three-inch deep corn emerges faster in exclusive test!

Published on: Jun 16, 2010

There's already been one surprise in the test that Indiana Prairie Farmer and the Tippecanoe County Extension Service are carrying out at the Meigs farm, part of the Throckmorton Research Center, an outlying Purdue University farm. The site is located north of Romney. The test is supported by Precision Planting, Tremont, Ill.

The goal is to compare combinations of planting depth, downforce pressure on seed openers and driving speed in a replicated plot. Due to wet weather, the test wasn't planted until May 27. So the results discussed here are specific to one planting date, at a time about two weeks past when you would ideally plant corn. It was their first opportunity to plant at the site this year.

Planting depths were one inch, two inches and three inches deep. "Many farmers have been planting deeper, and we're interested to see how that works out," says Jeff Phillips, Tippecanoe County Extension Ag Educator. The one-inch depth was measured carefully. All seed were covered, and the average depth was one inch. The test was planted with a six-row John Deere vacuum planter. The ground, fairly heavy, naturally wet soils, was worked the night before the test, at the first opportunity to work it without it being too wet.

When Phillips returned less than a week after planting, corn was already poking through the ground. The plot received nearly two inches of rain between planting and when he visited for the first time after planting. Without grabbing his plot layout sheet, he was sure the plots where he could see corn down the row would be the corn planted at an inch of depth. The ones not coming up yet very well must be the plots where the planter was set to plant three inches deep, where the soil was cooler. Soil temperature measurements confirmed the 3-inch depth was six degrees F cooler than the one-inch deep, although the 3 inch deep was still about 77 degrees.

Phillips was shocked when he finally looked at the plan. His guess was reversed. The shallow plots were struggling to emerge. The plots planted two inches and three inches deep were the tallest and most uniform.

It took a while to come up with a theory. "Apparently the soil dried out on top after planting," he says. "A few of the plants in the one-inch depth laying in moisture came up. But most of them apparently needed more moisture to get them up. It would have been interesting to see what would have happened if it hadn't rained an appreciable amount since planting.

It would also be interesting to see results if the test had been planted into cooler soil, say May 1. If the test can continue, that will be the goal next year, Phillips concludes.