Growth analysis of spring and summer seeded annual Medicago spp.

Understanding patterns of summer and fall growth and dry matter partitioning of annual medics (Medicago species) in the north central USA should be useful in developing harvest management recommendations for these legumes. Our objective was to describe changes in biomass yield and biomass partitioning to leaf, stem, and floral fractions during development of annual medics. Five Australian annual medic species and 'Nitro' alfalfa (M. sativa L.) were planted in spring and summer at St. Paul and Rosemount, MN. Leaf to stem dry weight ratio (L:S) of medics declined with maturation of both spring and summer seedings. Whole plant maximum DM yield averaged 5395 kg ha^-1 for spring seeding and 3786 kg ha^-1 for summer seeding, and these yields occurred from 10 to 14 wk after planting depending on species and environment. 'Sapo' (M. rugosa Desr.) and 'Sephi' (M. truncatula Gaertn) were consistently among the highest in leaf and stem yields for spring seeding, and 'Sava' [M. scutellata (L.) Mill] was consistently among the highest in leaf and stem yields for the summer seeding. 'Harbinger' (M. littoralis Rhode), 'Santiago' (M. polymorpha L.), and Sava were consistently the earliest legumes to flower and the earliest to achieve maximum flower and pod yields during summer growth. They also had the highest flower and pod yields. Flowering of annual medics was not fully expressed during fall growth because of the temperature and daylength changing pattern. Varied yield responses of annual Medicago species will necessitate species-specific harvest management practices.