GreenSeeker tool might help reduce your nitrogen costs

Handheld crop sensors such as the GreenSeeker can be used to estimate in-season nitrogen needs in corn.

Have you heard of GreenSeeker? It might be another tool that can help to reduce your nitrogen costs. Photo by Ricardo Costa, MSU Extension.

Nitrogen (N) is the most commonly applied nutrient and one of the most expensive inputs in corn production, averaging from 13 to 18% of the variable costs depending on the type of crop rotation. On the other hand, the nitrogen cost-to-benefit ratio usually exceeds that of other fertilizer inputs.

Nitrogen can be lost in several ways such as through volatilization, denitrification and leaching. It is best to apply nitrogen when corn has its greatest need for this nutrient (in general, 30 to 45 days after emergence) to avoid unnecessary nitrogen losses. For example, 30% of all your broadcast applied urea followed by six days without rain can be lost (these losses can be even higher in sandy soils). For more information on corn nitrogen guidelines, see these Michigan State University Extension articles by MSU soil fertility specialist Kurt Steinke: “Corn nitrogen guidelines and focusing on the right rate” and “Targeting corn nitrogen strategies for improved resilience.”

To minimize losses, corn producers can apply a smaller amount of nitrogen at or before planting and come later with a sidedress application. Since nitrogen levels can change drastically after the first application, producers can rely on a variety of methods such as the presidedress nitrate test (PSNT) and the chlorophyll meter readings among others to help determine how much nitrogen to apply for a maximum return to nitrogen application. The goal is to make sure crop yield is not limited by lack of nitrogen throughout the life cycle.

This article will review the use of the GreenSeeker handheld crop sensor by Trimble. The GreenSeeker was developed at Oklahoma State University for use in wheat and later adapted for use in other crops such as corn and barley. Using this handheld crop sensor and nitrogen sensing methods were demonstrated at the 2019 MSU Ag Innovation Day on July 26.

A crop sensor can detect wavelengths of reflected light from the crop canopy and produce a normalized difference vegetation index value called NDVI that is correlated with leaf chlorophyll. Based on this information, sidedress nitrogen rates that are aligned with site-specific crop needs can be prescribed.

Establish a high-nitrogen reference area early in the season in each field to be tested (a small area where more-than-adequate nitrogen was supplied for the entire season). Readings at the high-nitrogen reference area can be taken after corn reaches the V6 stage, and the sensor should be held 24 to 48 inches above the crop. To obtain a representative reading, walk with the sensor while keeping the trigger engaged and maintain a consistent height above the target. The display updates continuously, providing an average when the trigger is released.

After measuring the high-nitrogen reference area, don’t forget to record the readings (values range from 0 to 1). You will need to measure the non-reference area as well following the same steps discussed above.

Use the chart provided by Trimble to estimate the nitrogen fertilizer rate. Locate the curve closest to your high-nitrogen value using the legend in the normalized rate graph (A); find the number that is closest to your non-reference area on the bottom X-axis (B); find where the colored line meets the bottom number and trace back to the Y-axis and record the number found (C).

Normalized rate graph

On the maximum yield chart, select your crop and the expected yield in bushels per acre (bu/ac). Find where the row and the column meet and multiply the found number by the number you found previously on Y-axis of the graph. The result will be the amount of nitrogen in pounds per acre you will need to sidedress to achieve your yield goal.

table maximum yield edit

Among the three techniques discussed during the 2019 MSU Ag Innovation day (PSNT, cholorophyll meter and the GreenSeeker), the GreenSeeker is the most user-friendly since it doesn't require taking soil samples or focusing on a specific corn leaf.

If you are interested in learning how to take PSNT samples or how to use the GreenSeeke,r watch these two short videos below.

Join the Field Crops Virtual Breakfast meeting series

In agriculture, things can change fast. To help growers keep up with weather, pests and crop management issues, the MSU Extension field crops team is holding free Virtual Breakfast sessions every week during the growing season via Zoom video or phone conference. These virtual meetings take place every Thursday morning from 7-7:30 a.m. starting April 25 through Sept. 5, 2019.

Participating is easy!

You can join using your computer or mobile device (audio and visual) following the Zoom link: Or, call in from your phone (audio only) by dialing 669-900-6833 and enter meeting ID 552-324-349.

To receive a weekly email reminder of the Virtual Breakfast, sign up at Participants receiving emails can opt in or out at any time.

Can’t make it Thursday morning? Watch the recording!

For those who cannot join on Thursdays at 7 a.m., the Virtual Breakfast sessions will be recorded for later viewing with closed-captioning on the Field Crops Virtual Breakfast webpage. Podcasts are also available on the iTunes and Spotify.

Don’t forget to follow us on social media. Stay up-to-date on what is happening in Michigan field crops by liking the MSU Extension Field Crops Facebook page or following @MSUEFieldCrops on Twitter.

Scheduled topics and dates

Note that these may change to cover breaking pest and weather situations.

  • Aug. 22– Corn silage disease and quality management with Manni Singh
  • Aug. 29 – Harvesting weed seeds with Erin Hill
  • Sept. 5 – Calibrating yield monitors with Dennis Pennington

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