Both L. angustifolius and L. luteus used soil K and applied K more effectively than canola and wheat to produce shoots (measured from dried shoots of 42-day old seedlings). For all amounts of K applied, including the nil treatment, the K concentrations were higher in canola and wheat shoots than in shoots of the 2 lupin species. Consequently, the 2 lupin species were less effective than canola and wheat at taking up soil and applied K, but were more effective at using the K taken up to produce shoots. The most recent cultivar of L. angustifolius, cv. Kalya, was less effective than the older Merrit cultivar at using soil and applied K to produce shoots, therefore future cultivars need to be screened for their ability to use soil and applied K. The K efficiency ratio for L. angustifolius indicated cultivars Kalya and 2141 were inefficient and the following cultivars had similar medium efficiency values: Myallie, Tanjil, Tallerack, Quilinock, Belara and Merrit. As measured in 42 day old seedlings, the diagnostic critical concentration of K in shoots required for 90% maximum yield of dried shoots was about (g K/kg) 40 for wheat, 37 for canola, 16 for L. angustifolius and 14 for L. luteus.