HIGH CA IS NOT THE PRIMARY FACTOR IN POOR GROWTH OF LUPINUS-ANGUSTIFOLIUS L IN HIGH PH SOIL

Poor growth of Lupinus angustifolius L. on alkaline soils has been sug gested to be due to effects of both high calcium concentrations and hi gh ionic strength in soil solutions on growth. This glasshouse study i nvestigated the effect of calcium supplied as either CaCO3 or CaSO4 to an acid soil on the growth of N-fertilized and N-2-fixing plants of L . angustifolius cv. Gungurru, and compared responses of L. angustifoli us and Lupinus pilosus Murr., an alkaline-tolerant species, to high io nic strength in high pH solutions. Increasing CaCO3 application increa sed soil solution pH, and decreased shoot and root growth and chloroph yll concentration in the youngest fully expanded leaflets of both Nz-f ixing and N-fertilized plants of L. angustifolius. The effect of CaCO3 in decreasing root length was prior to and more pronounced than that on shoot weight and chlorophyll concentration. Adding CaSO4 increased calcium concentration in soil solution by 1.7-6.6 fold and calcium con centration in leaves by 10-30%, but did not markedly decrease the grow th of plants grown at any rate of added CaCO3. Increasing pH in nutrie nt solution from 5.2 to 7.0 decreased shoot weight of L. angustifolius , but slightly increased that of L. pilosus. Plant growth of both L. a ngustifolius and L. pilosus was slightly decreased as solution ionic s trength increased. The effect of high ionic strength was similar wheth er CaCl2 or KCl was the source of ions. The results suggest that poor growth of L. angustifolius relative to L. pilosus on some alkaline soi ls is not caused by excessive calcium or high ionic strength, rather h igh pH effects on root extension appear to be the major cause of the p oor growth.