Launched last year, Cargill's InSite VRN (variable rate nitrogen) system writes prescription rates for N, based on a field's yield potential. A result of six years of development and on-farm testing, the computer program combines remote sensing with Global Positioning Satellite (GPS) mapping, reports Dan Froehlich, Cargill's U.S. agronomy manager. “Growers using InSite VRN last year gained up to $20/acre from fertilizer savings and higher yields,” he says.

Currently available for corn and wheat, InSite VRN converts a satellite image of a field into a yield potential map, based on a number of variables. “It can all be done over the Internet,” Froehlich explains. “Local sales agronomists have a good chance for one-on-one contact with customers as they plug in a field's soil type, cropping and yield history, average organic matter content and other data.”

Credit is taken for estimated N availability from manure, legumes, organic nitrogen mineralization, preplant nitrate levels and nitrates contained in irrigation water. The final result pinpoints variable rates and costs (based on local N-per-ton costs) to reach the grower's yield goal. VRN maps correspond closely to actual high- and low-yielding areas generated by a combine yield monitor.

“InSite determines a field's suitability for variable rate N before the grower or retailer incurs any cost, like they would with grid sampling,” Froehlich says. “If the VRN map shows little variability in yield potential across the field, we recommend staying with a lower-cost, flat-rate N application. In many cases it will reveal that a single N rate wastes money and can threaten the environment through overapplication.”

A standard formula calculates recommended N rates. For corn, it's 1.2 lbs. N per acre per bushel of projected yield, but growers can adjust the formula to fit specific situations.

“With InSite VRN, retailers have a tool to really help customers calculate fertilizer economics,” Froehlich says. “Variable rate might result in a savings of 50 lbs. N/acre, for example in a low-producing area. They can put that savings in their pocket, but more likely, they'll decide to reinvest it on areas of the field with highest yield potential.

“Without pushing yields, we've increased net income from just varying N rate,” he adds. Most InSite VRN use in 2002 was in southern Minnesota, the Dakotas, Nebraska and central Illinois.

The program, tested first by Cargill AgHorizon retail centers, is available for license to other dealers located in Cargill's major fertilizer markets for a flat per-acre fee. “With volume discounts and other incentives we offer, the dealer margin is usually much better than present margins on seed or crop protection products,” Froehlich comments.

InSite VRN fits many of the nutrient management programs being developed at universities. “If and when legislation demands it, we offer a really good tool for farmers to capture exact applications on a site-specific basis. If they're ever challenged on how much nitrogen they're applying to a field, we will be able to provide them precise documentation rather than relying on field averages,” Froehlich says.

This year, InSite users also can calculate variable rates for phosphorus and potassium. This function could replace grid sampling or allow growers to sample less frequently, perhaps every six years rather than four. “InSite is also a good fit for growers who are renting land and don't want to get involved in a long-term grid sampling, or growers switching to targeted zone soil sampling,” Froehlich adds.

Cargill is also working on InSite programs for rice, barley and cotton, as well as variable rate herbicide application and seeding.

For more information, contact Froehlich at 952/742-6212, send an e-mail to dan_froehlich@cargill.com, or log on to www.freeproductinfo/fin.net.

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