GROWTH ANALYSIS OF SPRING AND SUMMER SEEDED ANNUAL MEDICAGO SPP

Understanding patterns of summer and fail growth and dry matter partit ioning of annual medics (Medicago species) In the north central USA sh ould be useful in developing harvest management recommendations Far th ese legumes. Our objective was to describe changes in biomass yield an d biomass partitioning to leaf, stem, and floral fractions during deve lopment of annual medics. Five Australian annual medic species and 'Ni tro' alfalfa (M. sativa L.) were planted in spring and summer at St, P aul and Rosemount, MN. Leaf to stem dry weight ratio (L:S) of medics d eclined with maturation of both spring and summer seedings, Whole plan t 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 an species and environment. 'Sapo' (M. ru gosa Desr.) and 'Sephi' (M. truncatula Gaertn) were consistently among Bile highest in leaf and stem yields for spring seeding, and 'Sava' [ M. scutellata (L.) Mill] was consistently among the highest in leaf an d stem yields for the summer seeding. 'Harbinger' (M. littoralis Rhode ), 'Santiago' (M. polymorpha L.), and Sava were consistently the earli est legumes to flower and the earliest to achieve maximum flower and p od yields during summer growth. They also had the highest flower and p od yields. Flowering of annual medics was not fully expressed during f all growth because of the temperature and daylength changing pattern, Varied yield responses of annual Medicago species will necessitate spe cies-specific harvest management practices.