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Using GPS for soil sampling: growers of agricultural products, constantly under pressure to generate more crops at lower production costs, are using GPS and precision agricultural technology to work towards this goal.

Global positioning system (GPS) technology has become an integral part of farming in the past decade. Precision agriculture, the study and managementof variations within fields that can affect crop yield, has greatly benefited from the introduction of GPS, especially since its main aim is to use chemical treatments only where and when they are necessary.

Trimble, Sunnyvale, Calif., which provides advanced positioning products and solutions, reports that GPS is currently used in a variety of precision ag applications: mapping in-field features, soil sampling, variable rate application of fertilizer and chemicals, and manual and automated vehicle guidance.

The art of nutrient measuring

Using GPS guidance for pesticide and fertilizer application removes guesswork and human error. Historically, agronomists performed soil sampling by pulling cores at random locations around the field, then combining them to give a field average for fertilizer application recommendations. The next advance was when the grower would isolate specific areas within the field where crops did not do well and do a separate sampling to treat these areas with a different fertility program.

Royster-Clark, New York, N.Y., which provides field management solutions, uses GPS technology when measuring nutrients in the soil. Agronomists break the field up into grids, pulling numerous cores from each. These samples are sent for analysis, where lab specialists identify which nutrients exist in the soil. The data is then correlated with soil type into a database, which then determines which fertilizer is the most appropriate for each part of the field. This information is sent to a GPS device that tells farmers how to feed each unique section so it reaches its maximum potential.

"GPS allows growers to farm on a 'site-specific' basis, where fertility is monitored on a much smaller scale," says Andy Ackley, corporate agronomist at Royster-Clark. "Today, growers are much more accurate and precise, providing nutrients only where required." In fact, according to 9 Trimble, compared to traditional methods, there is a savings of 5-10% in the amount of herbicide and fertilizer used in this more accurate application process.

A new technique

A new step in agriculture from Veils Technologies, Salina, Kan., is the pH sensor, an on-the-go chemical property sensor. The Veris system uses GPS and the technology of soil electrical conductivity (EC) to identify areas of contrasting soil properties. When the Veils Sensor Cart is pulled through the field, it acquires measurements, geo-referencing them using GPS. The data collected by the Sensor Cart is then displayed on an instrument panel, along with its coordinates. The result is a map that identifies the contrasting soil conductivity.

"While EC mapping devices do not directly measure soil fertility," says Eric Lund, president of Veils, "conductivity maps frequently relate to nutrients, in part because the movement of mobile nutrients is related to soil texture, and also due to the effect soil physical properties have on productivity."

"The major advantage over current technology lies in its ability to collect more data more rapidly than with conventional soil sampling and lab analysis," he adds. "The denser data provides a more accurate PH map, resulting in a savings of lime application."

A rich future

Despite the differences in the two soil sampling techniques, GPS is helping both achieve the same goal: the management and limitation of the amount of fertilizer used on farms today. Ackley feels that the Clean Water Act and the subsequent need to reduce the amount of nutrients in our water systems will lead producers to use GPS technologies. Nutrient management, mandated by the Act, will impact the amount of fertilizer a grower can apply to his soil.

"We know where the excess nutrients can end up--our ground water, and the hypoxia zone in the Gulf," adds Land. "As soil sensors make dense data more available, US agriculture will have more accurate maps and improved models, resulting in greater application precision."

KEYWORDS * Precision Agriculture * GPS Guidance * Soil pH


Royster-Clark Inc. 212-332-2965,

Trimble Navigation Limited, 800-865-7438,

Veris Technologies, 785-825-1978,
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Title Annotation:Emerging Technologies
Author:Joyce, Lorraine
Publication:R & D
Date:Oct 1, 2003
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