Experimental plots that have been used to test the use of sludge as opposed to commercial fertilizer in growing corn drew keen interest last week from farmers in Loudoun County, the largest corn-producing county in Virginia.

Agricultural experts involved in the test do not expect corn production, which in 1982 was over 3 million bushels in Loudoun, to vary greatly between sludge and commercial fertilizer.

But they said last week that the use of sludge, which is free to farmers, may cut the cost of corn production nearly in half. In Loudoun County, this could have an important economic impact for farmers, who last year planted 48,000 acres in corn.

A crowd of about 80 farmers and professionals in farm-related fields, mostly from Loudoun and some from neighboring counties, attended the Corn and Soybean Research Field Day, held by the Loudoun Agricultural Research Foundation, the Loudoun Soil and Water Conservation District, the Virginia Cooperative Extension Service, and the Loudoun County Department of Natural Resources.

The afternoon session involved visits to the fertilizer test plots and other plots testing seed varieties and tilling methods.

The groups visited the plots at the Bob James farm near Purcellville and the Bill Kelley farm near North Fork, walking up and down rows of corn and soybeans, scrutinzing demonstrations of different methods of tilling, and debating pros and cons of sludge as a fertilizer.

At the second test plot, the four groups in cooperation with the Department of Agronomy at Virginia Tech in Blacksburg had planted various plots of corns and then fertilized each with a different type of fertilizer. One of the plots was fertilized with sludge from the Blue Plains sewage treatment plant in Washington, another with commercial fertilizer.

The purpose of the experimental plots is to give area farmers a chance to study and consider new methods of farming, as well as new varieties of seeds.

The effort is supported by the Agricultural Research Foundation, formed earlier this year, as a way for farmers to share information without using their own farms for experiments.

Results of the corn-growing fertilizer experiment will be known only after the corn is harvested later this fall, said Gary Hornbaker, extension agent with the Extension Service office in Leesburg.

But Hornbaker does not expect production results to vary much from the sludge-fertilized plot to the one with commercial fertilizer. "We're supplying the plants with the same elements, just in a different form," he said.

The apparent advantages in the use of sludge are two, said Dr. Tom Simpson from Virginia Tech. It is free to farmers and it adds organic matter to the soil, thereby improving the texture of the soil.

Farmers can have sludge applied to their cropland at no cost, usually once every five years. Because most farmers fertilize their land each year, they would go back to using commercial fertilizer in between applications of sludge. So the economic advantage of using sludge would in most cases occur in one year out of five.

The treatment facilities pay private companies, who transport and apply the sludge. The only nutrient lacking in sludge but needed by crops is potash, which costs about $10 an acre, said Hornbaker. Lime, another necessary element, is used in processing the Class A sludge at the treatment plant.

So using sludge would cost about $10 an acre as opposed to almost $100 when using commercial fertilizer, Hornbaker said. Since about half the cost of corn production is the fertilizer, a farmer's production costs would be cut in half by using sludge, Hornbaker said.

"I'm not saying everybody's going to use sludge," he said, "but if you put the saving of $100 an acre on 49,000 acres, it adds up real quick."

The use of sludge to fertilize cropland is recommended by the Department of Agronomy at Virginia Tech, Simpson told the group last week.

Harry Jones, a farmer from Fauquier County who attended the afternoon session, has used sludge on his pasture and hayfields at his 165-acre beef cattle farm. He is pleased with the results, he said. "Anybody who knows anything about it recommends it."