Understanding which component has the greatest influence on yield is vital when managing lucerne (Medicago sativa) crops to maximise the production of high-quality forage. However, both yield components and plant morphology are affected by interactions between environment conditions and plant genetics. Field experiments across three environments (dryland at Cambridge: 500 mm annual rainfall, brown sodosol soil type; dryland at Elliott: 1200 mm annual rainfall, red ferrosol soil type; and irrigated at Elliott) in Tasmania, Australia were undertaken to investigate the yield, yield components and plant morphology of four lucerne cultivars; DuPuits, Grasslands Kaituna, SARDI 7 and SARDI 10 under cutting. The effect of cultivar on dry matter (DM) yield was different in each environment, with Grasslands Kaituna achieving the highest yield (P < 0.05) in dryland environments, while no difference in DM yield among cultivars (P > 0.05) occurred under irrigation. Stepwise linear regression consistently confirmed mass per shoot as the yield component with the greatest influence on DM yield for all cultivars and environments. Shoot density also had an influence on DM yield in two of the three environments. DuPuits had the highest leaf : stem ratio in all three environments and slower morphological development in two of the environments. Management practices across all environments and cultivars should aim to increase mass per shoot to maximise yield. Of the cultivars examined Grasslands Kaituna is the most appropriate for dryland conditions in Tasmania, while all cultivars examined were suited to production under irrigation.