FORAGES Yield and Quality of Forage Soybean

R7 stage (one seed pod at mature color; 50% of leaves yellow) produced forage that was similar in quality to Tall forage soybean [Glycine max (L.) Merr.] cultivars in maturity alfalfa harvested at early bloom. When soybean was groups V, VI, and VII have been developed to supply forage. Our objective was to determine the effect of harvest date and row spacing grown as an intercrop with corn, the forage CP concenon the forage yield and quality of these new soybean cultivars. We tration was increased by 30 to 43% compared with corn grew forage and standard grain soybean in Minnesota with harvests alone (Herbert et al., 1984). Forage yields of the soybean in early and late September. Average maturity of tall forage soybean and corn intercrop were comparable with those of the was R3 (early harvest) to R4 or R5 (late harvest) and average maturity corn monoculture. Sod-seeding soybean into tall fescue of grain soybean was R6 (early harvest) to R7 (late harvest). Herbage (Festuca arundinacea Schreb) increased forage yield by of forage soybean was mostly leaves and stems at both harvests, 300% compared with tall fescue alone and increased whereas herbage of grain soybean contained an average of 400 and the CP concentration of the forage by 10% (Ocumpaugh 595 g kg21 pods at the early and late harvests, respectively. There et al., 1981). was no harvest date 3 soybean entry interaction for forage yield or forage quality. Forage and grain soybean had similar forage yields As soybean matures from stage R1 (beginning bloom) (|8.8 Mg ha21). Because adapted grain soybean was more mature to R7, the leaf proportion declines (Fehr et al., 1971). and had a greater pod proportion than forage soybean, grain soybean Changes in the stem proportion with soybean maturahad greater crude protein (CP) and lower fiber concentration than tion are less consistent. Hintz and Albrecht (1994) reforage soybean. Average forage CP for forage and grain types was ported that the leaf concentration of grain soybean de146 and 218 g kg21, respectively, while neutral-detergent fiber (NDF) creased from 708 g kg21 at R1 to 168 g kg21 at R7. concentration was 523 and 400 g kg21, respectively. Decreasing row Meanwhile, the stem fraction increased from 292 g kg21 width from 76 to 25 cm increased forage yield 0.8 Mg ha21 but had at R1 to 383 g kg21 at R5 (beginning seed development) no effect on total herbage quality. and then declined to 283 g kg21 at R7 as the pod and seed components increased. The harvest of soybean for forage at R6 (full seed) S was introduced to the USA in the mid to R7 maximizes both the dry matter yield and forage 1800s and was initially promoted as a forage crop quality (Hintz et al., 1992; Munoz et al., 1983). However, (Williams, 1897; Arny, 1926). Hackleman (1924) conwhile the dry matter yield of soybean forage typically cluded that “...soybeans are the best annual nitrogenous increases with advancing maturity, changes in the forage seed and hay-producing plant.” By the late 1940s, the quality are less consistent. This is due to changes in the focus had shifted almost entirely from forage to soybean proportions of the leaf, stem, and pod fractions as well grain production. Soybean use for forage in the northern as the translocation of nutrients to the grain and inMidwest has been limited to situations where there is creases in the lipid concentration of the seed (Hanway a shortage of forage from other sources or when frost and Weber, 1971). Hintz et al. (1992) reported that damage limits grain harvest. There is now an opportuCP concentrations declined from R1 to R3, remained nity for increased use of soybean as a forage in Midwest constant between R3 and R5, and increased from R5 crop rotations because of the increased use of corn (Zea to R7. Whole-plant fiber concentrations increased from mays L.) silage and the decreased reliance on alfalfa R1 to R5 and decreased from R5 to R7. (Medicago sativa L.) by livestock producers. Reducing row spacing from a traditional width of 76 Limited research on use of soybean for forage shows cm to 25 cm or less is recommended to enhance soybean the potential benefits of soybean as a forage crop. Hintz grain yields (Naeve, 1999). In southern Minnesota, grain et al. (1992) reported forage yields from grain-type soyyields are typically increased by about 5%. Likewise, bean in Wisconsin ranging from 2.4 to 7.4 Mg ha21, Hintz et al. (1992) reported that for grain soybean, a depending on the stage of maturity at harvest. They 20-cm row spacing produced more forage than a 76-cm concluded that grain soybean cultivars harvested at the row spacing. They also observed that decreasing row spacing increased the stem diameter but that row spacing had no effect on the total forage quality. C.C. Sheaffer, J.H. Orf, J.G. Jewett, Dep. of Agron. and Plant Genetics, Univ. of Minnesota, 1991 Upper Buford Circle, St. Paul, MN Tall forage soybean cultivars in maturity groups V, 55108; and T.E. Devine, USDA-ARS, Weed Sci. Lab., BARC, 10300 Baltimore Blvd., Beltsville, MD 20705. Minnesota Agric. Exp. Stn. Abbreviations: ADF, acid-detergent fiber; ANOVA, analysis of variJournal Series no. 00-13-0143. Received 27 Jan. 2000. *Corresponding ance; CP, crude protein; NDF, neutral-detergent fiber; NIRS, nearauthor ([email protected]). infrared reflectance spectroscopy; WISC.BK, Wisconsin Black soybean. Published in Agron. J. 93:99–106 (2001).