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Space age farming

Variable-rate technology

When it comes to applying fertilizer, the common practice is for the farmer to take a variety of soil samples from the field, calculate the average nutrient need and then apply the same amount of fertilizer over the entire area. This does not, however, reflect the varying conditions of the soil. The same holds true when seeding or applying herbicides.

With variable-rate technology (VRT), the farmer can optimize crop production by applying the right amount of fertilizer or seed to match the different conditions within the field.

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VRT starts with detailed information on land and soil conditions, such as a yield map, satellite photographs and soil samples from areas tagged with Global Positioning System (GPS) coordinates. With the help of a computer program, the farmer calculates the unique blend and rate of fertilizer or seed needed for each zone of the farmland. This digital “prescription map” is then transferred to a computerized controller installed in the cab of the tractor, allowing the farmer to vary the application rate as the tractor moves up and down the field.

In more advanced VRT systems, the prescription map is entered directly into a sprayer or seeder that is outfitted with a GPS receiver. Changes in fertilizer or seed application are then automatically made on the fly with sensors that adjust the rate accordingly.


This piece describes how variable-rate technology provides valuable information about soil conditions, helping farmers optimize crop production. It is supported by a video case study on how Aberhart Farms Inc. in Saskatchewan uses this technology for its canola crop.


On the next page:

Soil mapping

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Quiz :

What is a yield map?

A general view of how much a field is being watered
A detailed picture of grain harvested from each sector of the field
A detailed view of the amount of fertilizer being applied to the field