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An eye on nitrogen

To better manage nitrogen applications, Tom Snider Jr. first went the split-application approach: preplant anhydrous ammonia with a strip-till pass, followed by a small dose in the starter at planting, and then a final sidedress application. “I don’t apply nitrogen in the fall at all,” says the McCool Junction producer.

His latest step in nitrogen efficiency — variable-rate N — came last year when he equipped his cultivator with GreenSeeker RT200 crop sensors to measure the plant canopy for nitrogen content as a basis for changing rates on the go.

“I was pleased with the system, but the technology is still new,” Snider says. “I still have more questions to ask and some modifications to make.”

Four sensors on the 12-row-wide cultivator — each sensing three rows of plants in 30-inch-row corn — measure plant vigor, or greenness, and send that data to a Trimble monitor in the cab. The monitor uses the data to determine the appropriate rate and “tells” a Hiniker controller to apply those rates in the field.

At a glance

McCool Junction farmer strives for better nitrogen efficiency.

In 2011, he installed optical sensors on his cultivator to scan corn plants.

Readings of plant nitrogen content are used for variable-rate application.

Use of optical canopy reflectance sensors to measure nitrogen status is an evolving type of ground-based remote-sensing technology. According to Richard Ferguson, a University of Nebraska-Lincoln soil specialist, three sensors are on the market: Trimble’s GreenSeeker, Ag Leader’s OptRx and Topcon’s Cropscan.

A strip that has adequate nitrogen applied is often used as a reference for the sensors to compare against the rest of the field. Snider intends to use that “nitrogen-rich” reference strip this year, but in 2011 he relied on soil sampling to help determine the on-the-go nitrogen prescription developed by the GreenSeeker system.

After one year, he’s not ready to claim big yield gains. “Yields were every bit as good and, in some cases, slightly better than in 2010,” he says.

For Snider, the goal is “applying the right amount of nitrogen, in the right location, at the right time in real time.”

Where he needs it, he adds, is on areas with higher yield potential, areas that the sensors “see” as lusher green.

“On some clay sidehills that are reflected as lighter green or yellowish, the system reduces the rate,” he says. “I’m putting on nitrogen where I need it. Poorer-yielding areas won’t respond to higher rates.”

In 2011, Snider used the variable-rate, on-the-go approach on 1,000 acres of corn, applying nitrogen with a cultivator sidedress trip at about the V-9 growth stage. He had already applied 120 pounds of nitrogen preplant, plus a minor amount in a 10-34-0 starter application. His sidedress variable-rate trip applied nitrogen in a range from 60 to 90 pounds per acre, depending on crop needs.

He’s considering equipping a sprayer with the GreenSeeker sensors this year to apply the sidedress treatment at a later growth stage.

This article published in the March, 2012 edition of NEBRASKA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.