WSP07639 - Laserfiche WebLink

Home Browse Search

EC mapping helps farmer know soil By Tom Doerge Measuring soil quality just got easier. With soil electrical conductivity (EC) mapping, precision farmers can quickly and accurately characterize soil differences within farm fields without spending a large sum of money. Electrical conductivity is the ability of material to transmit electrical current. Electricity in soils is conducted through moisture-filled pores between soil particles. Soil EC correlates to soil properties affecting crop productivity, including salt content, soil texture, cation exchange capacity, drainage conditions, organic matter level and subsoil characteristics. Soil EC data and EC maps of a field show clearly defined soil areas, accurately identify transi- tion zones between soil types and indicate ways to vary application rates of nutrients or other crop inputs. Soil EC maps can help farmers explain yield variation and adjust management deci- sions to boost yields, reduce input costs or accurately predict the benefits from whole-field improvements. Tim Godfrey, a precision ag farmer in Jonesville, Mich., uses EC mapping to pinpoint soil sample collection locations on his 2,500-acre farm. "I feel a lot more comfortable about money spent at the soil lab because more logic went into selecting the soil samples and they have more meaning," Godfrey said. He estimates a 10 percent to 20 percent decrease in soil analysis costs. Mapping Soil EC Mapping soil EC requires a field vehicle equipped with a differentially corrected GrS receiver and an EC measuring Veris 3100 soil EC mapping system. device. One device uses electro- magnetic induction (EMI) and measures electromagnetic fields created when an above-ground source injects electromagnetic energy into geological materials. The strength of the secondary electromagnetic field is directly proportional to the soil EC An equipped vehicle traverses the field in a series of closely spaced passes, collecting input from the GrS receiver and the EC measuring device at one-second intervals. This technique collects about 50 EC readings per acret compared to about one per 2.5 acres with grid soil sampling. Mapping at this density will identify soil inclusions that are 0.25 acres or larger in size. When compared to yield or soil survey maps from the same field, soil EC maps identify obvious relationships between soil type boundaries and crop yield patterns. A more rigorous analysis would involve rasterization of the EC data into square grid cells, shown at right. The average EC values from each cell then is compared to the corresponding average yield values using linear regression or other statistical techniques. mapping will not replace soil sampling and laboratory analysis for nutrients and other properties. but it does make sampling more efficient. By using soil EC maps, growers usually can reduce the number of soil sampling points by 20 percent or more and get the same amount of information. Because soil patterns are unlikely to change, soil EC maps are accurate management tools for long-term use. "You spend the money once," Godfrey said, "and reap the benefits for years to come because soil characteristics don't change." Farmers can use soil Be maps Soil EC Mapping Benefits The cost of soil EC mapping is $5 to $7 an acre, a one-time expense for most fields. Soil EC . e> 8 ~ to guide soil sampling, assign variable rates of crop inputs, fine- tune NRCS soil maps, and improve the placement and interpretation of on-farm tests, salinity diagnosis and drainage remediation planning. For Godfrey, EC maps provide more than precise soil information. "The biggest advan- tage is the peace of mind I get because my data are legitimate indications about what is happen- ing in my field. It's hard to put a price tag on that." Tom Doerge is a precisioll farming agronomist with Pioneer Hi-Bred [ntemational. Tel: (515) 334-6999; Emai1: doergeta@phibred.com. CTIC Partners 7 April 2000