DATE: 8/31/04

CONTACT: Dr. Ahmad Khalilian, (803) 284-3343, ext. 230

WRITER: Tom Lollis, (803) 284-3343, ext. 241

On the farm

Electricity gets down in the dirt

BLACKVILLE – It’s no shock for any good South Carolina farmer that understanding the soil is essential for success.

It may come as a shock for some, however, that a little electricity may make understanding the soil a lot easier.

Equipment tested at Clemson University ’s Edisto Research and Education Center for the past six years can produce a Global Positioning System (GPS) map that will show exactly where the different types of soil are in a field, whether light, heavy or somewhere in between.

Called the Veris 3100, it does all this by measuring the conductivity of the soil with electrically charged discs or coulters, according to Ahmad Khalilian, research agricultural engineer.

Heavy soils, those containing a lot of clay and organic matter, are better conductors than light, sandy soils. So, why is it important to know about soil texture?

“Soil texture is important for making all sorts of agricultural decisions, whether it’s for applying irrigation, fertilizer and pesticides, or for deciding whether to deep till to break up the hardpan in the subsoil,” said Khalilian.

“The best thing about this equipment is that it allows a farmer to divide a field into zones and manage each differently for fertilizer, nematodes, weed control or irrigation,” he said. By putting exactly what is needed in each zone, a farmer can save time, energy and money while being more environmentally friendly.

One set of sensors on the Veris 3100 takes readings to a depth of around 36 inches and another set measures the top 12 inches.

“Most nematode samples are taken in the top 12 inches of soil,” said Khalilian. Nematodes have their environmental preferences. Columbia lance and root knot nematodes like sandy soils. Spiral nematodes like heavier soils and ring nematodes live only in sandy soils.

“If you have heavier soils, you know there is less of a chance of having Columbia lance or root knot problems,” said Khalilian.

Soil insects such as Southern corn rootworm prefer poorly drained, less sandy soils with high organic matter, while lesser cornstalk borer will have much higher populations in sandy soils.

Sixty percent of the state’s cotton producers still use soil-applied herbicides to combat weeds such as Florida pusley, cutleaf evening primrose and common purslane, which Roundup will not control. Product labels require that soil-applied herbicides be matched to soil properties.

“We tested that by dividing a field into three different zones and applying different application rates using a variable rate applicator,” said Khalilian. “To get 80 percent control of morningglory using Cotoran we needed only about a quarter pound per acre of active ingredient in sandy soils. It took four to five times than amount in heavier soils. Those higher rates in sandy soil severely damaged 50 percent of the cotton.”

In a test to control nematodes he increased cotton yields by 7 percent using 34 percent less Temik with a variable rate applicator compared to applying a uniform amount across the entire field, as farmers have traditionally done.

“With the nematicide Telone, we increased yields by 5 percent while we cut back on the amount of chemical by 78 percent compared to the standard rate,” said Khalilian. The cost for the standard rate application is $36 per acre. That was cut to $7 per acre with the variable rate system.

“If the savings were figured on 1,000 acres, the savings would be $29,000,” he said.

While systems for measuring soil electrical conductivity are available commercially, they cost around $12,000, and Khalilian expects only larger farmers to buy it or several farmers to go together and share it. Commercial fertilizer and chemical applicators in some other states offer the service to farmers for around $5 per acre, which Khalilian said is well worth the cost. He said it’s only a matter of time before applicators begin offering the same service in South Carolina .

“Farmers who make arrangements through their county agents can borrow our system and try it on 50 acres to see what a difference it can make for management decisions,” he said. Nearly 20 farms across the state have been mapped with the Edisto REC equipment.

Khalilian said a farmer can almost estimate what kind of yield he’s going to get from each part of the field by looking at an EC map.

“If you overlay a yield map at the end of the season over the EC map, they will match perfectly,” he said.

To see how accurate the equipment is, it was tested on the farm in six different fields. GPS-referenced soil samples were taken from areas measured by the Veris EC meter and lab analyzed for soil texture.

Khalilian said that to do a soil texture map the old-fashioned way would take about 50 samples per acre. It would cost about $500 per acre, based on a lab analysis fee of $10 per sample.

“If your fields are uniform, the way many are in the Midwest and in the Plains States, you don’t need this equipment, but you don’t need precision agriculture in that case, either,” said Khalilian. “Where fields are not uniform, like in the Coastal Plain, you want to match inputs to the areas where you have yield potential. EC helps you do that.”

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