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Seek out best planting combination

You can argue that the most important activity in the spring is planting seeds correctly at the right depth, with the right downforce on the units, driving at the right speed. The Indiana Prairie Farmer/Precision Planting study attempted to sort out how important it is to make the right choices.

Precision Planting, Tremont, Ill., provided funding. 1st Choice Seeds, Milton, provided a LibertyLink hybrid. Spectrum Technologies, Plainfield, Ill., provided extra weather stations to monitor soil temperatures at various depths. Purdue University’s Throckmorton Research Center near Romney provided the land, crew and equipment. Jeff Phillips, Tippecanoe County Extension ag educator, provided the expertise in designing the test and analyzing results.

So what was learned from 108 six-row plots, each 100 feet long? “If you planted May 27 in Lafayette, Ind., in 2010, your best choice was to plant 2 to 3 inches deep, run 5 to 6 miles per hour, and set your planter on medium downforce,” Phillips says.

Key Points

Shallow-planted corn lagged behind all season, yielded less.

Slower speed produced better spacing, but not higher yields.

The results apply to this particular set of conditions.


“The point is that while we found some surprises and made some interesting observations, this study is a snapshot of what happened at one location with one set of weather conditions at one planting date,” he says.

“We missed the early-planting window and then a three-week weather delay forced us to wait until May 27. We would love to try this again, planting around May 1. If the conditions are entirely different, the results might be totally different.”

The attempt

Organizers settled on testing three seeding depths: 1 inch, 2 inches and 3 inches; three downforce pressures: light, medium and heavy; and three planting speeds: 4, 5 and 6 mph. To include all the combinations, each full replication contained 27 individual plots.

The entire experiment was replicated four times in what scientists call a randomized complete block design. Basically, Phillips used a program that picks numbers representing plots at random. Where individual plots land in the field is by chance. Pete Illingworth, of the Throckmorton farm crew, planted the plots on May 27 with a six-row John Deere 7200 Max Emerge planter equipped with the vacuum system.

Since the plot was worked one way and planted the opposite way, the ride was a bit bumpy, particularly at 6 mph. The poorly drained to somewhat poorly drained timber soil was worked the evening before planting, as soon as the crew judged it was dry enough. The plot was prepared with conventional tillage.

The conditions

While moisture conditions seemed good at planting, five to six warm days followed before rain fell. That becomes important when looking at seed depth results, Phillips says.

Aztec insecticide at 7.9 pounds per acre was applied at planting because the hybrid did not have corn borer or rootworm protection. All plots were sidedressed on June 11 with 55 gallons of 28% nitrogen per acre. Due to another rainy period, spraying was delayed until July 6.

“Soils were warm when we planted,” Phillips says. “There was a difference between the three depths, but the coolest was 75 degrees F.”

Torrential rains came in mid-June, after sidedressing. A handful of plots were severely affected, first by ponding, then by nitrogen loss and rank weed growth. About 12 plots were removed from the study, based on observations at the end of June. That still left three reps for nearly every treatment. Phillips used statistical techniques to still produce credible data.

“The yield was half on some of those plots, and it was clearly due to the weather, not treatments,” he says. “We ran the data with and without stunted plot data, and the trends were similar. We felt it wasn’t fair to include them because we wanted to see the effects of the treatments, not unusual weather conditions.”

The results

“My biggest shock was visiting the plots 10 days after planting and noting that the 2- and 3-inch depths were up and even, and the 1-inch depth was struggling,” Phillips says. “The plots planted at 1-inch depth ran behind in maturity at every checkpoint, and yielded significantly less than the other two depths. In fact, the 1-inch depth was more than 25 bushels per acre behind the 3-inch planting depth.”

There were virtually no yield differences due to downforce setting. However, the medium setting, based on standard deviation, which is based on the distance between plants in the row, was significantly better at spacing than the lightest setting. There was no statistical difference between the medium and heavy setting.

Four miles per hour produced significantly better plant spacing than 5 mph. Both 4 and 5 mph were better than 6 mph. However, the standard deviation for 6 mph was still 2.46 inches, a respectable number.

Yields for 5 and 6 mph were virtually identical. Yield at 4 mph was lower.

“But we can’t say with 90% confidence that it wasn’t just due to chance,” Phillips says.

Final population for 4 mph was higher than at the other two speeds. One theory holds that extra plants in a very dry, hot year might hurt yields instead of help them, even if spacing is better.

Nanda writes from Indianapolis. He’s director of genetics and technology at Seed Consultants Inc. E-mail Nanda@seedconsultants.com or call 317-910-9876.

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Note: LSD = 0.9; growth stages determined on average of three plants per plot using leaf collar method. Source: Jeff Phillips, Tippecanoe County Extension

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Search for answers: Pete Illingworth plants plots at the Throckmorton Research Farm. He varied settings, hoping to find the best planting speed, depth and downforce pressure.

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

All rights reserved. Copyright Farm Progress Cos. 2011.