Lupin takes up less potassium but uses the potassium more effectively to produce shoots than canola and wheat

We compared the potassium (K) response of canola (Brassica napus L. cv. Karoo), spring wheat (Triticum aestivum L. cv. Camm), narrow-leaf lupin (8 cultivars of Lupinus angustifolius L.), and yellow lupin (2 cultivars of L. luteus L.) in a glasshouse experiment. The following measures were used: yield without added K; K required for 75% of the maximum yield; K required to achieve a K concentration in shoots of 20 g/kg; K required to achieve a K content of 50 mg K/pot in dried shoots (K concentration multiplied by yield); and, for the L. angustifolius cultivars, the K efficiency ratio (yield for the nil-K treatment divided by yield for the largest amount of K applied). 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.