Walter Hasselbring's secrets for achieving the nation's highest corn yield are a lot of bull. The national corn king credits his top-notch crop to generous applications of the real thing from his cattle and his buffalo herd, Illinois' largest. But he teases unsuspecting visitors with another success secret, telling them he grew 296 bushels per acre last year by serenading his corn. ``I tell them plants respond to music, so at crucial times I stroll through my cornfields singing to the plants and you can almost see them grow,'' chuckled Hasselbring, who has grown the nation's best-yielding corn crop seven times in the last 15 years. The National Corn Growers Association sponsors the contest, and 2,057 farmers entered during the 1989 growing season. There were seven divisions, depending on the type of tillage, the area of the country and whether irrigation was used. ``Farmers compete not only to see who can grow the most corn but also to come up with new management ideas that could make all farmers more efficient,'' said John Campen of the St. Louis-based association. Hasselbring's yield was the highest in the 1989 contest, said Campen, and established a U.S. record, topping his 1975 mark of nearly 289 bushels per acre. His winning yield was more than twice the 138-bushel-per-acre average in Iroquois County, where Hasselbring farms 1,800 acres in east-central Illinois with his two sons. ``You can do everything else right, but if you don't get the rain, you won't win,'' Hasselbring said in an interview Wednesday. A high level of fertility also is crucial. Hasselbring uses about 300 pounds of nitrogen per acre _ roughly twice his normal rate. He adds manure from his cattle herd and his 105 buffalo. Farmers pay $50 to enter the competition. They plant a contest plot of at least 25 acres. Hasselbring's corn went in May 5, and the growing season was ideal. As the crop matured, Hasselbring walked his contest field. ``I could tell things were looking up,'' he said. ``After all these years farming, you just get an inkling of what's going on. But, when it was harvested, it was even more than we expected.'' Judges approved by the National Corn Growers Association supervise the harvest of at least 1.25 acres from each contest plot. Hasselbring's was combined Nov. 13-14. Rules require farmers to harvest at random intervals so they cannot pick the best area of the field. University of Illinois agronomists Fred Welch and Bob Hoeft agree with Hasselbring that shooting for 300-bushel yields on a large acreage is a big gamble given high growing costs and the inability to control weather. ``Winning might not mean getting the best dollar-return for your inputs, and it is profit, not a record yield, that is really important for commercial farmers,'' Welch said. Although the national corn surplus is approaching 2 billion bushels, the idea that more corn means less profits isn't what would keep farmers from adopting high-yield techniques, Campen said. It is the expense of producing such yields. ``The economics, at least today, on a broad scale basis wouldn't warrant it,'' he said. Officials at Fred Gutwein & Sons Inc., a family-owned corn and soybean seed company based in Francesville, Ind., that provided hybrids to Hasselbring, said his success improved Gutwein name recognition and sales. ``Our hybrid met the challenge,'' said sales manager Eric Gutwein. ``But, it takes a very special individual like `Duke' Hasselbring to achieve the pinnacle seven times.''