David I. Bransby, Arturo Martinez, Chet Norris, and Malcom Pegues

Preliminary tests at several locations in the AAES system have shown that a new variety of forage soybeans could become a valuable component of present and future forage systems in Alabama and neighboring states. In the first year of evaluation, a soybean cultivar bred specifically for forage production grew to seven feet in height and provided between 3.4 and 6.8 tons per acre of dry matter.

When soybeans first were developed as a crop in the United States, the original intention was to use them for both forage and grain production. Over the past several decades soybean grain has become an extremely valuable ingredient of concentrate diets for animals, and soybeans also are used in a wide range of industrial products. Therefore, the current focus of most soybean breeding programs is on grain production.

Despite the mainstream interest in grain production, the USDA Agricultural Research Service has developed improved varieties of soybeans for forage. The initial concept was to use forage soybeans as companion crops with corn to increase protein content of silage. This led to the development of three new varieties of forage soybeans that are currently being licensed by the USDA to private companies for seed increase and commercialization.

Tyrone, which is the new USDA-developed cultivar considered most suitable for the South, was evaluated for production and forage quality in preliminary tests in Alabama during the summer of 1998. Plots of Tyrone were established at the Gulf Coast Research and Extension Center in Fairhope (South Alabama), the E. V. Smith Research Center (EVSRC) in Shorter (South-central Alabama), and the Tennessee Valley Research and Extension Center in Belle Mina (North Alabama) in May 1998. Plots were planted on a 30-inch spacing, and standard practices for production of soybean grain were followed. Forage yield was measured at all three locations, and grain yield was measured at Fairhope. Plant samples were separated into stem, leaf blade, petiole or leaf stalk, and pods. These samples were analyzed for crude protein (CP) and total digestible nutrient (TDN) concentration, which indicate the nutritional value of the plants as a forage (see the table).

At the E. V. Smith Research Center, forage soybean plants grew to a height of six to seven feet (see title photo) and yielded 6.7 tons of dry matter per acre. At the other two locations plants reached a height of about five feet and yielded 3.4 tons per acre. The difference in yield between the EVSRC and the other locations was probably related to the difference in early season rainfall; in May and June the Tennessee Valley and Gulf Coast sites received only 4.24 and 3.04 inches of rain, respectively, while the EVSRC site received seven inches. When compared with average hay yields of 2 to 2.5 tons per acre for Alabama, forage production recorded in these preliminary tests is attractive. Grain yield from the Gulf Coast test was 39 bushels per acre, compared to 46 bushels for grain-type varieties.

About half the forage yield of the crop was in the form of stem material; the other half was comprised of leaves and young pods. This concentration of yield in the stems was visually evident, in that stem bases of the largest plants were more than one inch in diameter. Crude protein concentration was high in leaf blades and pods, but low in leaf petioles and stems. The TDN concentration was also highest in leaf blades and pods, but low in stems. Low TDN suggests a high level of lignification (an excessive development of fiber in the plants that often makes them less palatable to cattle) in this part of the plant. Forage quality would likely have been better if the plants had been harvested at an earlier stage of maturity.

Initial results from this study suggest that forage soybeans may be a useful crop for producing silage or hay in Alabama. However, commercial scale yields, the length of time needed to cure the crop, and the extent of leaf shattering during hay production are not known. Consequently, further research is in progress to obtain this information.