Eye in the Sky

October 1, 2010 11:53 AM

On a plain, 8½"x11" sheet of white paper, red, green and yellow streaks reveal the rows where Leon Knirk’s corn fields had adequate nitrogen this year and, likewise, where they didn’t.

“We could even tell where my dad had buried the foundation of an old building at one time, because it showed up red on the map,” says Knirk, who farms and runs a cattle business with his wife, Jennifer, near Quincy in south-central Michigan.

The map Knirk references resulted from remotely sensed imagery of his fields, a type of high-tech aerial photograph based on Normalized Difference Vegetation Index (or NDVI; see sidebar for more information).

“NDVI imagery gives us a really accurate layer of spatial information that we can use to help Leon and other farmers fine-tune their management and agronomic practices,” explains Missy Bauer, Farm Journal Associate Field Agronomist.

Bauer is one of Knirk’s advisers for the 2010 Ultimate Farm Quest program. The program is designed to help Knirk take his operation to a higher level of performance. Farm Journal will report on his experiences with the program throughout the coming year.

The accuracy of the map is significant, Bauer says. NDVI maps show information on a meter-by-meter basis as opposed to yield maps, which provide data based on a 20' to 35' swath, depending on the width of the combine header that is used.

Timing is important. Two of the best times to implement the aerial mapping process are just prior to tasselling and just before drydown, says Nicholas Morrow, a field representative for GeoVantage, Inc., based in Swampscott, Mass. The company provides NDVI imagery mapping services.

“When you implement it depends on what you want to achieve,” he says. “There are literally hundreds of uses for this technology.”

Bauer says that when NDVI mapping is executed early in the season, farmers can see and correct certain problems such as insufficient nitrogen levels in corn.

Along the same lines, Morrow adds that NDVI mapping after canopy closure supports what he calls guided crop scouting.

“You can get a lot more acres scouted in a day, because the imagery tells you the areas that need your attention and those that don’t,” he says.

At harvest, NDVI mapping provides information that correlates closely to yield maps. Morrow says the technology helps to verify what farmers are seeing from their combine and on their yield monitors.

In addition, he adds that some state corn and soybean associations use NDVI maps to validate their test plot results and even go so far as to throw out yield results that don’t mesh
with the maps.

Knirk plans to use information from the maps to fine-tune the agronomic management zones within his corn fields. He and Bauer believe this will make his variable-rate applications of nitrogen a more exact process in fields come next spring.

Return on investment. An NDVI aerial imagery service costs between $2 and $4 an acre on average. While there are no startup fees, most companies do require customers to commit to a minimum number of acres. GeoVantage has a 2,000-acre minimum, but two or three farmers can pool their acres to reach that number.

Morrow says that farmers who want to give the technology a try can derive the best return on their investment in fields that contain varying soil types and terrain. “That’s where you’ll get your greatest payback,” he says.

Morrow encourages farmers to work with their local seed retailer, Extension specialist or consulting agronomist to locate companies that provide NDVI mapping services. These
resources also can help evaluate and implement decisions based on information the maps provide.

Mapping Plant Health

The Normalized Difference Vegetation Index (NDVI) is a spatial measurement that uses a combination of near-infrared and red light reflectance to assess the relative vegetation biomass and vigor in a farmer’s field.

Measurement results are aligned with an image file such as a historical map, satellite image or aerial photograph, and the resulting information forms the basis for a detailed, color-coded map.

NDVI measurements that detect healthy vegetation in a field show up as green areas on the map.

The green turns to shades of yellow and red wherever the NDVI measurements detect variations and less-than-desirable plant health. The colors used to denote plant-health variations are selected by the company that provides the NDVI mapping service.

Such variations can result from many different factors, including inadequate nutrient levels, poor drainage, compaction, disease and insect problems and even equipment malfunctions.

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