EFFECT OF SOWING DEPTH AND WATER POTENTIAL ON SEEDLING EMERGENCE OF LUPINUS SPECIES

Large differences in responses of germination and seedling emergence t o water potential and sowing depth were detected among Lupinus species varying substantially in seed size. Seeds of 7 species (L. pilosus, L . atlanticus, L. albus, L. cosentinii, L. luteus, L. angustifolius and L. hispanicus) germinated rapidly in moist sand (-0.05 MPa). Germinat ion of ail these species was reduced when seeds were raised in sand in which water potential was increased from -1.0 to -0.5 MPa at 4 days a fter sowing, and then to -0.2 MPa at 18 days after sowing. Percentage germination after 20 days was much higher in small-seeded species (L. hispanicus, L. angustifolius, L. luteus) than in large-seeded species (L. albus, L. atlanticus, L. pilosus). Germination responses were rela ted to rate of water uptake by seeds from sand at 0.5 MPa. Seedling em ergence of pre-germinated seeds sown at different depths in moist (-0. 05 MPa) and dry (-0.3 MPa) sand varied greatly among 6 species. An inc rease in sowing depth from 4 to 8 cm retarded seedling emergence to a greater extent than a decrease in water potential in L. pilosus, L. lu teus, L. cosentinii and L. atlanticus. L. angustifolius seedling emerg ence was less affected by variation in sowing depth and water potentia l than other species, although a decrease in water potential had a rel atively large effect on seedling emergence from 4 cm. A decrease in wa ter potential also decreased seedling emergence of L. albus more than deeper sowing. Seedling emergence responses of 4 species (L. angustifo lius, L. luteus, L. albus, L. atlanticus) were compared in an experime nt where dry seeds were sown in dry sand (-0.3 MPa) at different dista nces above a moist sand (-0.05 MPa) zone in specially constructed tray s. Small-seeded species (L. angustifolius and L. luteus) emerged most rapidly from the shallowest sowing (3 cm below the surface, 9 cm above the moist zone), whereas the large-seeded species L. albus and L. atl anticus emerged most rapidly from sowings at intermediate depths (6 an d 9 cm). L. albus and L. angustifolius seedlings emerged far more rapi dly when sown on the surface of the moist sand (12 cm) than did L. lut eus and L. atlanticus, and were far more tolerant of variation in sowi ng depth. The implications of these findings are discussed with partic ular reference to improving lupin crop establishment following early d ry sowing in the West Australian wheatbelt.