A DETERMINATION OF PROTECTIVE MICROHABITATS FOR BACTERIA INTRODUCED INTO SOIL

Survival studies with rhizobia introduced into loamy sand showed that a kaolinite amendment of the soil improved the survival of Rhizobium, and that bentonite had a very strong positive effect on rhizobial survival. The survival level was significantly higher in soil amended with 10% than with 5% bentonite. The amount of water present in the bentonite amended soil had a significant influence on rhizobial survival; in drier soil, survival levels were highest. For the loamy sand, the loamy sand amended with 5 and 10% bentonite or with 10% kaolinite, the number of rhizobial cells surviving on day 57 after introducing 2.5-5.0 x 10(7) cells g-1 dry soil could be described using the distribution of pores from three size classes in a mathematical relationship. Pores with necks < 3-mu-m and between 3 and 6-mu-m positively affected the survival of introduced rhizobia whereas pores with necks > 6-mu-m had a negative effect.