RELATIONSHIP BETWEEN GRAIN-YIELD AND PLANT POTASSIUM CONCENTRATION IN LUPINUS ANGUSTIFOLIUS CV UNICROP

The relationship between K concentration in the plant at various growth stages and the grain yield of L. angustifolius cv. Unicrop was derived from a rates and times of application of KC1 field trial. Critical levels were defined as those associated with 90% of maximum yield. Critical % K levels in the whole tops were 3.1 at the 4-6 leaves stage, 2.9 at 8-10 leaves, 1.5 at 1st flowering, 1.2 with flowers on higher order laterals and 0.9 post flowering. The effect of plant part sampled was examined at early flowering. Critical levels at the stage were 1.2% K for petioles 1-5, 0.6% K for petioles 6-10, 1.3% K for leaves 1-5, 0.5% K for leaves 6-10 and 2.1% K in the growing point of the plant. Grain K concentrations were very insensitive to changes in supply, and are of little use as a diagnostic tool. The ratio of K concentration in pods to that in seeds increased from 0.5 under extreme deficiency to 1.3 under conditions of adequate supply, and should be a useful diagnostic tool at maturity.