Using Variable Rate Nutrient Technology for Precise Crop Nutrients

A trend toward higher crop nutrient costs may accelerate a trend to help manage it.

Technology used to apply variable rate nutrients (VRN) was a program focus at the recent Minnesota Wheat and Barley Growers’ Prairie Grains Conference.  Sponsored by Bayer, Kevin Poppel and Roger Knudson of Triangle Agronomy Services, Lake Park, Minn., (www.triangleag.net ) discussed how to turn computerized field data into input cost savings and crop production profits with VRN, a site-specific farming practice.

Site-specific farming is simply producing crops more efficiently.  Or as North Dakota State University extension fertility specialist Dave Franzen puts it, site-specific farming is “doing the right thing at the right place at the right time.”

Franzen has a backgrounder on site-specific variable-rate fertilizer application, online at www.ext.nodak.edu/extpubs/plantsci/soilfert/sf1176-2.htm It’s part of a series on site-specific farming, with more links at the bottom of the online backgrounder, in which he points out that the idea of varying the rate of fertilizer across a field is not new, and has been conducted in a rough manner by growers since at least 1929.

Back then, early attempts at site-specific application meant spot treating different rates of fertilizers to different areas of the field. However, methods to measure and distinguish variable rates – such as flagging, guidance using swath widths, and counting rows – weren’t easy to use and observe.

Today’s equipment and technology allows easy variable-rate nutrient application. To determine whether a variable-rate application is needed, soil sampling is needed to determine what rates should be used and where the material is to be applied. Then, with an on-board computer together with GPS, a producer can apply fertilizer at the recommended rates with much more accuracy and assurance than in the past.

Poppel explains site specific farming as gathering information about field locations, farming history, and management practices, then managing that data to allow producers to create scenarios that define and compare costs. Who should use VRN?  “Any grower who wants to lower input costs and maximize yields,” he says, by correcting limiting factors in small grains. “It allows producers to manage the high cost of crop nutrients by understanding the variability in the field which limits yield potential,” he says.

Knudson adds that by using VRN, producers can move away from “farming the average” by better estimating yield responses.

Their program, supported by Centrol Crop Consulting, Precision Partners, Inc., and Cargill, allows producers to evaluate a crop’s yield potential before paying for VRN and applying more fertilizer.  Poppel says the technology is easier and less expensive to use than what many producers first think. Poppel and Knudson’s business, like other precision ag providers, help put the pieces of information in place to allow site-specific farming, including GPS field borders, crop rotation and yield average history, yield goals, and soil organic matter percentages.

Jeff Nesbitt of Precision Partners, a provider of precision ag equipment and services based in Fergus Falls, Minn. (www.precisionpartners.com), says average savings of nitrogen alone can be around $5.00 per acre through VRN, by moving nitrogen from areas of a field that may produce poorly no matter the fertilizer rate (because of salinity or drainage, for instance), to higher producing areas of a field where the nutrient is used more efficiently. Doing so can also help manage plant lodging, he adds.

Knudson says that the best parts of the field generally have higher organic matter content, increasing soil tilth, water holding capacity, and nutrient release. He advises producers to match yield maps with topography and fertility maps to see what is really happening in the field. With yield maps, he says producers can develop field levels with multi-year yield stability zones. This includes areas of the field that are consistently high or low, inconsistent, or average in yield.

Using all available maps can answer why field zones react as they do.  Reasons may include drainage ditches, fertility, tree lines, or topography.  He said irregular shapes in maps indicate naturally occurring circumstances like water patterns, topography, or soil type.

How long does it take to pay for the technology? Gary Wagner, a Crookston, Minn. producer who is widely recognized as a precision-farming expert, says he saved $7,000 in wild oat herbicides alone in a four-year period.  Along with better crop nutrient efficiency, Wagner says the technology also allows him to vary his seeding rates throughout a field.

Wagner recommends producers ease into the technology; learning more about the concept and then trying it in a few fields would be a great start. Once in place, he says site-specific farming gets easier every growing season, just like doing anything that’s new.

“It’s about working smarter, not harder,” says Knudson, about site-specific farming.