Three 6'-tall forage soybean varieties from USDA should help growers boost the protein content of corn and sorghum silage.

Tom Devine, USDA plant breeder at Beltsville, MD, says the varieties - Derry, Donegal and Tyrone - will probably be used in mixtures with sorghum, millet or corn.

Plot evaluations indicate the tall beans can yield almost a ton of protein per acre under ideal conditions.

The beans share a long-season, late-growth characteristic that lets them make fuller use of rain and sunlight in late summer and early fall, when corn or sorghum water use tapers off, Devine points out. They resemble other beans in growth until August.

Unlike other soybeans, the new silage beans continue to put on substantial growth well into September.

So says Dave Starner, director of the Virginia Tech Northern Piedmont Ag Research and Extension Station at Orange, VA.

The new varieties are not patented but are covered by the 1994 plant protection law. USDA is currently making them available to seed producers for multiplication and distribution. Farmers could see them in time for 1999 planting.

Meanwhile, soybean-companion crop evaluation will continue, according to Devine.

"We're working to learn how to make best use of their potential," he comments. "They respond differently in varying conditions and locations."

The height and aggressiveness of the companion crop will also influence the rate of bean development until late in the growing season when the bean plants stretch out. There's some indication their tops may vine into the tops of the interplanted corn or sorghum for additional support and lodging resistance.

Devine emphasizes that the new beans are not intended for grain production. They've been cut for hay in Oklahoma, but mainly are for silage.

Donegal is a Group V variety that he suggests may be best adapted for Pennsylvania and New York. In replicate tests over several years, it yielded 66% more dry matter than adapted grain-type beans.

Derry is suggested for the northern Midwest. A Group VI variety, it's exceptionally tall with good lodging resistance. Like the others, it has been extensively evaluated in Virginia, North Carolina, Minnesota, Iowa, Arkansas, New York and Pennsylvania.

Tyrone, a Group VII soybean, is late maturing with high forage-production potential. It's recommended for Southern-state forage growers.