Ecological studies on Azotobacter in Egyptian soils.

The present survey includes 156 representative soil samples. Results obtained confirm the richness of Egyptian soils, particularly the Nile Valley soils, in Azotobacter (60% of the samples contained greater than 10(3) colonies/g soil). Colony counts were lower than MPN estimations. Glucose is recommended for use in plating medium. Among the environmental factors affecting Azotobacter densities in soils of Egypt are: organic carbon content, total soluble salt content, pH and type of the soil, depth, cultivation, and standing crop. Pot experiments performed indicated that high incubation temperature (30, 37 degrees C) markedly enhanced development of Azotobacter as well as the gains of total nitrogen, particularly when soils are amended with 1% maize straw and incubated for 12 months. A. chrococcum was the most prevalent speciee; A. vinelandii was encountered as well. The analysis of some samples, representing soils of near Middle Eastern as well as North African countries, indicated the common occurrence of Azotobacter in these soils. Beijerinckia could not be detected in any of Egyptian or non-Egyptian samples examined.