Crop Scene Investigation - 28 Solved: The curious case of Quinn's corn

Monday, December 6, 2010

by BERNARD TOBIN

The variation in emergence in Quinn's corn was caused by worn double disc openers on his corn planter, which created a W-shaped seed trench rather than a V-shaped one. This produced great variation in seed depth which led to the uneven emergence in the later-planted fields.

Dekalb agronomist Sean Cochrane explains that when he inspected Quinn's planter, he used his tape measure to determine that the discs had considerable wear and were one to 1.5 inches smaller than the recommended diameter for discs suitable for the planter.

The wear also meant that the discs did not touch. For the planter to make an efficient V-shaped trench that would set seeds at a consistent depth, the discs should touch at the front and maintain a two-inch area where they are touching or connected. To confirm his diagnosis, Cochrane slid paper between the two discs to determine that they did not touch at all.

"They were worn to the point where they were no longer really usable," explains Cochrane. "That was causing the hill in the seed trench (a W rather than a V), which contributed to the seed depth problem. Some of the seed would sit on the top of that hill and would be planted very shallow. When the closing wheels came to push that seed in, they kept it up high on the ridge and it actually didn't get very deep." Consequently, seed depth ranged from some being virtually on the surface to others being an inch and three quarters deep.

Cochrane says the problem got worse as Quinn worked his way through the fields because, once the disc diameter begins to shrink, the rate of wear accelerates quite rapidly with continued use.

Cochrane has a couple of tips for growers like Quinn who find themselves in tough planting conditions. "Lesson number one is patience. Wait for good soil conditions before putting any type of equipment into it. And, make sure that seed-to-soil contact is going to be anywhere from adequate to excellent, not adequate to poor, when the seed actually hits the bed."

A simple planter maintenance check can reveal problems before seed is planted and yield is lost, says Cochrane. "I highly recommend that everybody put a tape measure to their discs and their disc openers to make sure they are touching at the front and have that two-inch area where they are connected. They should also make sure the disc diameter is within the guidelines recommended for the particular planter."

Congratulations to Tom MacGregor, Crysler, for his correct answer. Tom commented in his response that this problem is aggravated "in a rushed planting season with a short weather window, when speed tends to creep up." BF