SOME FACTORS ASSOCIATED WITH POOR EMERGENCE AND GROWTH OF LUCERNE SEEDLINGS IN SOILS FROM 'RUNOUT'

In a series of glasshouse experiments, emergence and growth of seedlings ofluceme (Medicago saliva L.) cv. W airau were studied in soils collected from run-out lucerne crops at nineteen locations in the nuijor lucerne-growing regions of New Zealand. Observations were made on the incidence of seedling failure before and after emergence and growth. The effect of amendment with lucerne residues on emergence and growth was also noted. There was a wide range of seedling emergence among soils and in the amount of seedling loss due to Pythium spp. before and after emergence. Seedling emergence and growth were significantly increased after the soil was treated with an airsteam mixture at 60° for 30 minutes. It is concluded that many of the soils tested contained organisms which were inhibitory to the early growth of lucerne plants. Addition oflucerne residues to the soils significantly reduced emergence and growth of seedlings. Since old lucerne roots can be a source of fungi pathogenic to lucerne it is recommended that such material be allowed to rot away completely before resowing lucerne. Additional