Growth, Development, and Yield of Soybean Lines Developed for Forage

Recently, soybean [Glycine max (L.) Merr.] cultivars have been developed specifically for use as a forage crop. The objective of this study was to determine the effect of maturity group on and compare the agronomic performance of forage and grain soybean cultivars in Iowa. In 1994, 13 forage‐ and five grain‐type cultivars were studied. In 1995, one additional forage cultivar and grain cultivar were each evaluated. Node number, plant height, lodging, and dry matter accumulation were measured biweekly during the growing season. By 135 days after planting (DAP), forage cultivars yielded 5 to 19% more dry matter than ‘Sherman’, which had the greatest yield among grain cultivars. Forage cultivars were 37 to 69% taller than ‘Biloxi’, the tallest grain cultivar, which may partially explain the greater lodging of the forage cultivars compared with the grain cultivars. Forage cultivars initiated reproductive growth 60 to 88 DAP, whereas the locally adapted Sherman cultivar initiated reproductive growth 55 DAP. Forage cultivars produced more dry matter than grain cultivars, but had a lower leaf/stem ratio and leaf + pod/stem ratio in August and September, respectively, which may reduce forage quality. Forage cultivars developed in Pennsylvania generally accumulated more dry matter than forage cultivars developed in Virginia by late August, but initiated reproductive growth sooner and produced less dry matter by late September. The significant productivity differences observed between forage and grain cultivars suggest the potential of breeding to improve the forage potential of soybean.