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United States Department of Agriculture

Agricultural Research Service

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Precision Agriculture
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Precision Agriculture or Site-Specific Farming 


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"Precision agriculture" or "site-specific farming" may be new terms to you, but you'll be hearing a lot more about them as farming turns the page to a new era of technical agriculture.

For centuries, farmers have known several facts to be self-evident concerning every field they farm. First of all, all soils in a field do not have the same uniform soil composition. In other words, no two soils are created equal. Secondly, all soils do not capture rainfall or drain with the same efficiency. Therefore, a farmer must become acquainted with the multiple soil types per field and know how much nutrients, water, and/or pesticides will be needed for each soil type. Refer to "Ag-tivities" at the bottom of this page for activities that demonstrate soil diversity and the ways to handle this.

To begin the journey into "precision-ag ," every 21st century farmer will fall behind if he does not have a PC. Once you've taken the plunge into the PC market, it will be easy to utilize the software that makes precision farming the blessing it is designed to be.

Illustration of satellites orbiting the earthLet's say, for example, that you need a map of your 300 acre fields. No problem. Geographic positioning systems (GPS) are available to allow you to locate position of features such as soil type, weeds, water holes, boundaries, and obstructions. These systems access orbiting satellites in a triangulation pattern that can be accurate enough to locate a quarter buried in a field, but are usually within a few meters. GPS systems enabled US tank crews to navigate accurately in the desert during the Persian Gulf War, giving them a big advantage over opposition forces still using roads and landmarks. More recently, a fighter pilot was lost behind enemy lines in Bosnia. His handheld GPS was the technology that allowed rescuers to locate him and get him out of the area.Image of differential Global Positional System Farmers are now accessing these same military satellites. Another, more familiar, use of this system is in the locaters now available on some cars. According to the commercials, you can follow the directions on a readout in the car to aid you in finding a certain location. Some delivery companies are also making use of the system to find where exactly your package may be. The obvious result for farmers is that this information allows them to know how much or how little water, nutrients, and pesticides would be necessary for relevant positions within the fields. Also, seeding rates can be adjusted along with tillage. Refer to "Soiled Minds" at the bottom of this page for links to activities that demonstrate soil type variation.

Another way to use GPS data is to combine its positional information along with yield data to produce yield maps. Image of a yield map using GPS dataTo create these maps, the GPS system is used to note a combine harvester's position in a field while a yield monitor notes yield rate and/or other variables such as moisture content from a sensor that is mounted on or around the grain elevator of the combine. This data is recorded and a map created that usually uses different colors to indicate yield rate.

(Photographs above courtesy of "Precision-Ag Illustrated" magazine.)

"GIS" stands for Geographic Information System and refers to a system that interfaces with data captured from spatial reference points. In other words, GIS will interpret data that the GPS has sent using database software and a PC. Sounds like a bunch of alphabet soup, doesn't it?

Once soil maps are available, irrigation methods can be considered. One consideration is a site-specific center pivot irrigation system developed at the ARS in Florence, SC.Image of the site-specific center pivot irrigation systemThis is an irrigation system that applies the standard center-pivot irrigation principles and carries them a step further. It is calibrated to deliver nutrients, water, etc. to crops that are in a Close up image of the system in actiongiven field. The left photo is a close-up of the system in operation. Notice that delivery is from the bottom rather than the top as it is on conventional center pivot irrigation systems. The delivery is dependent upon need of the crop and takes into account the soil in which the crops are planted. It is so precise that you can plant different crops in the same field and irrigate them as needed. The upper right photo shows a field of soybeans being irrigated while the corn on the right also gets irrigated. The area between irrigation is being selectively untouched.


Schematic of the center pivotBecause the center pivot system moves in a circular pattern, as in the schematic diagram to the left, pie-shaped plots can be drawn and irrigated as needed. The photo to the near right is an aerial view of a field that is being used to research the center pivot system. The green sections are soy beans and the reddish sections of the pie have corn growing in them. If you look closely at the green areas, you may notice different shades of green. These are the aerial view of the center pivot
sections of the pie that have been treated in a specified manner. The lighter sections were irrigated while the darker sections were not. The section in the upper right hand portion of the photo is planted with old seed and is not really a part of the experiment. The area that cuts across the center of the photo is an access road. The circular bare spaces are where the wheels of the system pass through the field and the radiating bare spaces are also access pathways.

Variable-rate controllers (VRT's)also help in site specific farming. These set rate of delivery of nutrients,water, etc. dependent upon soil type as noted in your soil maps. The central "brain" of the system is the controller itself. This controls all of the machinery that monitors application rates for a sprayer, spreader, anhydrous ammonia applicator, and any spot spraying equipment. The controller may operate as a separate unit or may be built for a specific type of machinery. Most controllers are interfaced with a laptop computer modified so that the operator has access to data in the cab of the tractor, combine, etc. The entire setup allows the operator to view his position on a display as they move through a field. It also monitors application rates.


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Last Modified: 8/12/2016
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