ACTIVE MOVEMENT OF CHICKPEA AND BEAN RHIZOBIA IN DRY SOIL

Soil matric potential strongly influenced the movement of three strain s of chickpea and bean rhizobia in soil. The strains were able to move (albeit relatively slowly) in soils at matric potentials drier than t hat believed to be the limit for bacteria movement (-0.1 MPa). The non -motile and non-flagellated strain, 18A(str rif) moved faster than the flagellated and motile strains in soils at or drier than - 1.5 MPa ma tric potential, but slower than the other strains in wetter soil. The degree of motility and the presence of flagella were important factors influencing the movement of rhizobia in soils that had water-filled p ores larger than cell size. The role of flagella and motility became l ess important as water-pathways became smaller and discontinuous. The movement of rhizobia was less in.clay soils than in light-textured soi ls over the range of matric potentials investigated, possibly due to a dsorption to clay particles.