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Split-rate N trials leave unanswered questions after one year of testing

Ken Simpson applies nitrogen with a toolbar
COMPARE METHODS, TIMING: Ken Simpson piloted his own rig, applying N with a toolbar, while the Shelby County Co-op applicator applied N with Y-Drops in this cornfield.
Specialist says it’s not possible to draw conclusions based on two nitrogen trials in 2016.

Randy Overman and his son, Aaron, Peru, worked with Bob Nielsen and Jim Camberato in 2016 to see if splitting applications of nitrogen and applying some N later in the season would be beneficial to the corn crop. Several counties away, Ken Simpson, Morristown, also worked with the two Purdue University Extension agronomists on a field-scale trial.

Indiana Prairie Farmer visited both farms when late applications were made, and took pictures from the applicators and of the rigs themselves. You may have seen these images and read about these trials in previous stories. Now the results are in.

Because different application methods were used on each farm and weather conditions were different, it’s interesting to look at each trial separately, Nielsen says. “The most important thing to remember with both trials is that we’re reporting what happened on one farm in one year,” he emphasizes. “We would need a lot more trials under many more environments before we could make meaningful conclusions.”

Overman trial
In the Overman field, there were five treatments: 150 pounds of liquid N applied at V4, the normal method used by the Overmans; 99 pounds of liquid N at V4 plus 51 pounds applied with Y-Drops at the V15 stage of growth; that same rate applied by dribbling on the surface at V15; 75 pounds applied at V4 plus 75 pounds applied at V15 with Y-Drops; and that same split rate applied at V15 by dribbling N.

The results in bushels per acre were 197.3, 197.5, 195.4, 194.0 and 193.8, respectively (see chart below).

Nielsen and Camberato made these four observations:

• There was a significant difference by statistics. Even though it’s a narrow yield range, the least significant difference at the 0.10 confidence level was only 1.8 bushels per acre. That means the first two methods — applying all N upfront and the 99 plus 51 split with Y-Drops — were significantly different than the other treatments. “It’s basically saying that if we do this again, we’re 90% certain we should see similar results; effects were real, not due to error,” Nielsen says.

• More N later reduced yield. Even using Y-Drops, yield was lower when more of the N was applied later in the season compared to applying a bigger percentage at V4, Nielsen observes.

• Weather conditions could have been a factor. It didn’t rain for days after application, and the area was relatively dry for the next several weeks, with only 2 inches of rain in July. It’s possible dry weather impacted results, Nielsen notes.

• What "statistically significant" means. Statistically significant to a researcher doesn’t mean it’s economically significant.

The differences in this trial were small. When you put dollars and cents to the results on a field-scale, things can look much different, Nielsen says.

TEST THE CONCEPT: Aaron Overman helps set up the high-clearance sprayer to compare application using Y-Drops and dribbling N on top.

Simpson trial
Simpson owns his own high-clearance sprayer with a toolbar to apply N through coulters. The Shelby County Co-op obtained a rig this year equipped with Y-Drops and participated in the trial so Simpson, Nielsen and Camberato could get a look at coulter application versus application with Y-Drops.

The six treatments on Simpson’s farm were: 200 pounds of liquid N applied by Simpson at V3; 150 pounds of N at V3 followed by 50 pounds applied by Simpson at V9; 150 pounds applied at V3 plus 50 pounds applied by Simpson at V15; 50 pounds early plus 50 pounds of N applied by Y-Drops at V15; 100 pounds early with 50 pounds applied by Simpson at V15; and 100 pounds of N applied at V4 plus 50 pounds applied by Y-Drops at V15.

The results in bushels per acre were: 196.4, 197.7, 197.3, 201.7, 196.9 and 200.9. The LSD at 0.10 was 2.9 bushels (see chart below).

Here are four observations by Nielsen and Camberato:

• Two of six methods tested significantly better. The two Y-Drop applications were significantly different in research terms than the other methods.

• Yield differences were small. The advantage was still only in the range of 3 bushels per acre. At $3.50 corn, that’s about $10.50 per acre. Depending upon the cost to make the second application, it might be only a breakeven or slightly better than breakeven situation.

• Weather is always a factor. These results were again affected by weather conditions this year. Even though the difference was real, results might be different under other weather conditions.

• Results differed from previous trials. Simpson looked at split applications with Nielsen and Camberato over the past several years. This was the first year they applied with Y-Drops, and the first year they saw a true difference in yield based on how much N they applied and when they applied it.

Bob Nielsen, Purdue University

Bob Nielsen, Purdue University



TAGS: Management
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