A field experiment was carried out to investigate the effect of pre-sowing
inoculation of marjoram with Azotcbac!<:r cnroococcum, Bacil/us circuiens, vesicular
arbuscular mycorrhizae(VAM} or Iheir mixture in the presence of full or half of the
recommended field rate of the inorganic NPK fertilization on the planl growth, microbial
activities in the rhizosphere, volatile oil yield and chemical composition. Parameters
related to the above- mentioned measures of performance were recorded. Data of this
study showed that mixed inoculation with the three biofertilizers supplemented with
half dose of NPK gave the hiphest and significant increases in the growth parameters,
oil % and oil yield teddan' . as well as, the N. P and K % in plant herb. The above-
mentioned treatment increased the concentration of the constituents volatile oil,
geranyl acetate, cineole, linalool.limonene and c-Ierpenolene. while decreased the
concentrtion of a-terpineol compared with the control. Mixed inoculation also, raised
total microbial densities and also those of azotobacters and B,circu/ans in marjoram
rhizospheric soil and increased C02 evolution, N2-ase activity and mycorrhizal root
infection, as well as, spore production .On the other hand, inoculation with either of
A.chroococcum or B.circu/ans amended with half dose of NPK decreased the above-
mentioned parameters compared with uninoculated plants supplemented with Ihe full
dose of NPK fertilization, but VAM applied alone or in conjugation with the bacterial
partners significantly enhanced those parameters.