Effect of sowing depth and water potential on seedling emergence of Lupinus species

Large differences in responses of germination and seedling emergence to 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). Germination 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 after 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 related to rate of water uptake by seeds from sand at 0.5 MPa. Seedling emergence 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 increase 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. luteus, L. cosentinii and L. atlanticus. L. angustifolius seedling emergence was less affected by variation in sowing depth and water potential than other species, although a decrease in water potential had a relatively large effect on seedling emergence from 4 cm. A decrease in water potential also decreased seedling emergence of L. albus more than deeper sowing. Seedling emergence responses of 4 species (L. angustifolius, L. luteus, L. albus, L. atlanticus) were compared in an experiment where dry seeds were sown in dry sand (-0.3 MPa) at different distances above a moist sand (-0.05 MPa) zone in specially constructed trays. 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. atlanticus emerged most rapidly from sowings at intermediate depths (6 and 9 cm). L. albus and L. angustifolius seedlings emerged far more rapidly when sown on the surface of the moist sand (12 cm) than did L. luteus and L. atlanticus, and were far more tolerant of variation in sowing depth. The implications of these findings are discussed with particular reference to improving lupin crop establishment following early dry sowing in the West Australian wheatbelt.