When Ol' Man River began depositing millions of tons of Iowa and Illinois farmland in the Mississippi alluvial floodplain, he didn't discriminate between fields or even within fields as to what types of soils he put where.
More than one Delta farmer has lamented the fact that the soil type may change several times before he goes from one end of a field to the other. That diversity creates an ideal situation for site-specific management, says Roger Carter, a Clayton, La., farmer and consultant.
Carter is president of Agricultural Management Services, Inc., an agricultural consulting and farm management firm servicing or managing more than 50,000 acres of cotton and other crops. He also farms 1,200 acres of cotton and is part-owner of Concordia Farmers Gin in Ferriday, La.
“The use of variable rate technology, especially in the application of fertilizer and lime, is the simplest and most cost-effective way to begin with site-specific management,” he says.
Zone management of inputs is the most effective way to approach site-specific management, says Carter. “A management zone is a portion of a field that expresses a homogeneous combination of yield-influencing factors for which a single rate of a specific crop input is appropriate.”
To determine these zones, consultants and producers can use USDA soil maps, yield maps, satellite or aerial imagery, or Veris data, says Carter. Veris is a tool for measuring the electrical conductivity of the soil at various depths.
The Veris unit, he explains, consists of six coulters, two for sending out electrical or electromagnetic pulses and four for collecting the voltage drop from the source. Two of the receiving coulters are placed close to the source coulters for collecting topsoil data and two are further away for collecting data from 1 to 3 feet deep.
“Electrical conductivity has long been used to identify contrasting soil properties for environmental and geologic purposes,” says Carter. “It often correlates to soil properties affecting productivity, including clay content, texture and subsoil characteristics.”
Veris has certain advantages over imagery, he says. “Veris can measure depths of up to 3 feet while imagery can capture only what is seen above the ground. Topsoils are not always the same depth, and subsoils are not always the same types. Nematodes and nutrients vary beneath the soil surface.”
Cloudy weather also can affect imagery, he adds. Imagery, however, has certain advantages over Veris, he continues. “Veris data cannot be collected from wet soils, extremely dry soils, or when the existing crop is present. And the amount of acreage that Veris can cover is limited. Imagery can be done on thousands of acres with one picture. But both are very useful tools for a basis of site-specific management,” he says.
Harold Lambert, an independent agricultural consultant from Innis, La., first introduced Carter to the Veris rig. “We leased the unit from Harold in 2000 and Verised our first 750 acres. We collected the data and utilized the services of Maurice Wolcott, an LSU AgCenter expert on precision agriculture, to write prescription applications for nitrogen for the 2001 crop.
“We purchased an IPAQ handheld computer for $400, a Navman antenna for $300 and a TeeJet radar-controlled spray monitor for $2,200. We downloaded the prescription application into the IPAQ and made our first variable-rate application,” he says.
The results, says Carter, were “astounding.”
“We reduced Pix applications by 75 percent and appeared to enhance yields by 10 to 20 percent. We did, however, have to ground truth or observe on a zone-by-zone basis the effects of our application rates. There is little or no data available for determining exactly how much of any input may be needed based on Veris data, he says.
Adjustments were made in the prescriptions that were written for the 2002 and 2003 crops. “We currently have Verised more than 2,500 acres for five different customers and expect that the need for more Veris rigs will increase as the technology is better understood.”
Carter also expects to capture future savings through more precise applications of nitrogen, potash, phosphate, lime, growth regulators, nematicides, harvest aides and perhaps insecticides and fungicides. “Variable-rate seeding rates are currently available, and variable-rate seeding depth is coming. All will play an integral part in making the Veris data we collected a major factor in our overall economic viability,” he says.