Clays and the Survival of Rhizobium in Soil During Desiccation

Abstract

AbstractA study was conducted to assess the effect of drying on populations of two strains of Rhizobium japonicum and two cowpea rhizobia. The numbers of these bacteria fell markedly in soils undergoing drying. The extent of the decline varied with the strain and the soil. The decline in the population of a cowpea rhizobium occurred during the time of rapid water loss from four soils. The fall in numbers of three of the strains during desiccation was greater if the organisms were on glass beads than in soil. Illite did not increase survival on the beads, and kaolinite reduced the number of survivors of three strains dried on fine sand. Montmorillonite at the same concentrations protected against viability loss of two rhizobia undergoing desiccation on fine sand, but had no such effect on the more desiccation‐sensitive strain. The percent survival of three strains in a soil and in sand‐montmorillonite mixtures was directly related to the amount of water remaining after drying and was also affected by relative humidity. A possible relation between tolerance to desiccation and cell water content is suggested.