| Abstract: | Inoculated and non-inoculated seedlings of maize were grown in fertile clayloam soils of Egypt and Belgium under subtropical conditions provided in a greenhouse. Acetylene-reducing activity and microbial counts were determined during a period ranging from 6 to 12 weeks after sowing. Irrespective of soil origin, N2-fixing spirilla and Azotobacter were common under maize cultivation. Inoculation resulted in a transitional increase in their numbers at early stages of growth. Nitrogenase activity was not detected in the rhizosphere of young plants. The maximum activities measured (81 to 1,436 nmol of C2H4 g−1 h−1) occurred close to the 50 to 70% silking stage. Inoculation with N2-fixing spirilla, particularly in Nile Delta soil, doubled the amount of N2 fixed in a late period of growth (12 weeks), whereas inoculation with Azotobacter had no noticeable effect. |
