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Researchers develop new sweetclover

A new sweetclover breeding program conducted by Texas Agricultural Experiment Station-Overton researchers promises to give an old legume new life in central Texas and parts of eastern Texas. Drs. Gerald Evers and Ray Smith are developing a new sweetclover, with thin stems and a low coumarin content.

Well adapted to the alkaline soils and climate of central Texas soils, sweetclover used to be grown throughout the region up to the 1950s.

Sweetclover had some drawbacks, such as a thick main stem that limited digestibility and slowed drying when cut for hay. Sweetclovers also had a high coumarin content.

When sweetclover hay is not dried properly and subsequently becomes contaminated with mold, the coumarin converts to dicoumarol, a compound similar to modern blood thinners. Cattle eating the dicoumarol-contaminated hay can experience internal bleeding and, in some cases, die.

As with other legumes, sweetclover captures nitrogen from the air, lessening the need for expensive nitrogen fertilizer. Managed correctly, legumes can fix from 75 to 100 pounds of nitrogen per acre.

“Before the advent of cheap fertilizer, annual sweetclover was one of the most popular legumes used by central Texas farmers and ranchers,” Smith said.

“By the early '50s, sufficient sweetclover seed was being produced to plant 500,000 to 600,000 acres yearly.”

After World War II, however, cheap nitrogen fertilizer came on the scene, and all legumes, sweetclover included, lost favor.

Today, however, nitrogen fertilizer isn't so cheap. Also, because it's petroleum based, the price of nitrogen fertilizer is indirectly linked to natural gas prices and foreign politics.

In 1999, recognizing the need for improved legumes, Evers and Smith began looking at sweetclover again. Evers, a forage management researcher, and Smith, a legume breeder, thought sweetclover would have a place in large parts of Texas farmland if a variety could be developed with higher digestibility and low coumarin content.

Few improved pasture legumes were available for the alkaline soils in the 20- to 25-inch rainfall belt in the middle of the state,” Evers said.

Part of the solution was already in place. The Texas Agricultural Experiment Station at Weslaco released Emerald, a thin stem, readily digestible sweetclover in the 1950s. Because it had a high coumarin content, and the price of nitrogen fertilizer was low, there was little demand for the Emerald variety and seed was not produced.

Evers and Smith identified a low coumarin, biennial northern type sweetclover called Denta. Smith crossed Denta with Emerald and evaluated the first hybrids at the Texas A&M University Agricultural Research and Extension Center at Overton in early fall of 2001.

They then produced seed from approximately 70 Denta-Emerald hybrids in the spring of 2002.

Ten thousand plants from the 70 hybrids were planted in an Overton Center greenhouse in late August 2002. The thin-stem characteristics were easy to visually identify, and they used an inexpensive process to identify those fine-stem plants that also had low coumarin levels.

One-sixteenth of the resulting sweetclover breeding population had both fine stems and low coumarin.

Funds often dictate how soon a new variety can be brought to the public. Now, partially financed by a $15,000 grant from the Texas Department of Agriculture, Smith and Evers are testing and planting experimental sweetclovers at three sites: a private farm in Ellis County; the Stiles demonstration farm at Thrall in central Texas; and the Texas Agricultural Experiment Station at Beeville.

The selected sweetclovers represent four different maturities, from March to May. Winters at the three test sites range from mild to moderate to cold, enabling Evers and Smith to further refine the evaluation process.

If all goes well this fall, the two Experiment Station researchers expect the new sweetclover varieties to be available to producers by 2005.

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