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How To Use Aerial Images

You can get aerial images of your fields taken from planes or satellites. The question is how can aerial images help in setting variable rates?

ANSWER

The answer comes from Warren Bills, Agri-Trend Geo-Coach based in Calgary:

If you have an aerial or satellite image, you’ll be able to see your field in a totally different perspective and detect certain patterns that you may not have known existed. Using RapidEye satellite imagery or Real Shot aerial imagery, you also get the advantage of seeing and recording in the near-infrared.

The near-infrared (NIR) wavelength of light is not visible to the human eye, and has the ability to detect more subtle changes in vegetation density, plant health, and soil moisture than normal wavelengths of visible light. Measuring its degree of reflection is also indicative of the inner cell structure of the plant tissue, which can be related back to things such as plant health and drought stress.

Determining a recommendation for “variable rate” from any image isn’t necessarily an automated process. It will require knowledge of the field, a visit — groundtruthing — to the field with the imagery in hand, and agronomic expertise to make a confident recommendation that will yield a return.

The first question to ask yourself is, “What do you want to vary?” Some images will detect patterns of salinity, in which case the variable rate recommendation may be for reduced fertilizer in these areas. Some images will detect water logging problems and drainage issues. This variable rate recommendation may be for seed rate next year or drainage work in the off season. Other images may be used for variable-rate fungicide to lower risk and make this decision easier for you. There’s not a cookie cutter approach, but there is tremendous opportunity to be more efficient.

WHAT DOES AN IMAGE COST?

The cost of acquiring an image and getting a sound recommendation and variable rate card is probably going to range between $8 and $12 per acre. Once you have established different variable rate plans and management zones, you may not need to adjust them every year, so the cost of the program may be reduced in subsequent years.

A couple key things to remember with images for variable rate is that it is measuring variation from the ground up, not ground down. We aren’t really measuring soil or soil properties, as we do with soil testing and Veris machines. We can draw conclusions to these factors with good ground-truthing, farmer-and-consultant interaction, and field history. We also should combine other tools, such as soil and tissue tests, with the images to gain more confidence and accuracy on our recommendations. Skipping these seemingly obvious steps for variable rate could result in more damage than good.

ANY OTHER USES FOR THESE MAPS?

If you want to walk before you run, any kind of aerial or satellite image can be used for “smart scouting.” VRT isn’t the only immediate application for imagery. Using the images to guide you more accurately to the places in the field to take your tissue or soil samples from, or finding areas of initial concern to watch for disease or insect outbreak are other good agronomic uses for imagery. The more you know, the more you’ll grow.

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