THE INFLUENCE OF SOIL-WATER POTENTIAL ON THE GROWTH AND SURVIVAL OF ALFALFA RHIZOBIA IN THE SOIL

Growth and survival of alfalfa rhizobia (Rhizobium meliloti Dang.) fro m Pakistan and Nepal were studied in vials filled with sterile soil ma intained at -0.03, -1.0, and -1.5 MPa. The main effects of water level , rhizobial strains and length of exposure to desiccation and their in teractions showed a highly significant (P less than or equal to 0.001) effect on the number of rhizobia g(-1) of soil. Growth and survival o f rhizobia were highest in soil at -0.03 MPa followed by soil at -1.0 and -1.5 MPa. Highest cell counts were observed for strain UL 136 foll owed by strain UL 222 and the lowest was for strain UL 61. Two rhizobi al strains (UL 136 and UL 222) were most tolerant to desiccation and s howed highest growth and survival under low water potential. These two strains probably could be used as inoculants for alfalfa production u nder arid and semiarid environments.