THE EFFECT OF SOWING DEPTH AND DURATION OF WATERING ON EMERGENCE OF TROPICAL LEGUMES IN CLAY SOIL IN GROWTH CABINETS

The rate and final % emergence of 7 tropical legume species were exami ned at a range of sowing depths from 0-5 cm in trays of clay soil in a germination cabinet set to day/night temperatures of 30/20 degrees C. The species included are used or have potential for use in leys (Labl ab purpureus cv. Highworth; Macroptilium atropurpureum cv. Siratro; Ma croptilium bracteatum CPI 27404; and Macrotyloma daltonii CPI 60303) o r permanent pastures (Desmanthus virgatus cvv. Marc, Bayamo and Uman; Indigofera schimperi CPI 52621 and CPI 73608; and Glycine latifolia cv . Capella). The ability of soft seed of Indigofera schimperi and Desma nthus virgatus to either emerge as seedlings or retain viability durin g brief periods (1-4 days) of watering was also examined. The small-se eded Desmanthus virgatus and Indigofera schimperi successfully emerged only from depths of 2 cm or less. All the larger-seeded legumes emerg ed from the maximum depth of 5 cm. Indigofera schimperi was much slowe r to emerge than Desmanthus virgatus and usually required 4 days of go od soil moisture to reach 50% emergence of viable seed compared with 1 -2 days for Desmanthus virgatus. This resulted in greater emergence of Desmanthus virgatus than Indigofera schimperi given only 1-2 days wat ering. In some cases, soft ungerminated seed of Indigofera schimperi r emained viable following brief wetting and drying of the soil, and ger minated on a subsequent watering cycle. Possible implications of sowin g depth and rate of emergence are discussed in relation to establishme nt in the field.