Farmer Gary Wagner walks into his field where the summer leaves on the sugar beet plants are a rich emerald hue — not necessarily a good color when it comes to sugar beets, either for the environment or the farmer. That hue tells Wagner that he’s leaving money in the field in unused nitrogen fertilizer, which if left in the soil can act as a pollutant when washed into waterways, and in unproduced sugar, the ultimate product from his beets.
The leaf color Wagner is looking for is yellow. Yellow means the sugar beets are stressed, and when the plants are stressed, they use more nitrogen from the soil and store more sugar. Higher sugar content means that when Wagner and his family bring the harvest in, their farm, A.W.G. Farms, Inc., in northern Minnesota, makes more dollars per acre, and they can better compete on the world crop market.
To find where he needs to adjust his fertilizer use—apply it here or withhold it there—Wagner uses a map of his 5,000 acres that span 35 miles. The map was created using free data from NASA and the U.S. Geological Survey’s Landsat satellites and tells him about growing conditions. When he plants a different crop species the following year, Wagner’s map will tell him which areas of the fields are depleted in nitrogen so he can apply fertilizer judiciously instead of all over.
A farmer needs to monitor his fields for potential yield and for variability of yield, Wagner says. Knowing how well the plants are growing by direct measurement has an obvious advantage over statistically calculating what should be there based on spot checks as he walks his field. That’s where remote sensing comes in, and NASA and the U.S. Geological Survey’s Landsat satellites step into the spotlight.