Enhancement of nodulation and symbiotic nitrogen fixation by rhizobium japonicum in soybean plant as contribution of the asymbiotic nitrogen fixer azotobacter chroococcum
Yanni, Y.G.; Mohamed, Y.A.H.
Beitraege zur Biologie der Pflanzen 60(2): 207-222
A pot experiment was conducted at "Sakha Agriculture Research Station, Kafr El-Sheikh, Egypt" to study the effect of inoculation of soybean plant with the symbiotic N2-fixer, Rhizobium japonicum, with or without soil inoculation by a locally isolated strain of the nonsymbiotic one. Azotobacter chroococcum, in combination with fertilization by ammonium sulphate in the rates of 0, 20 or 40 kg N/feddan (feddan = 4200 m2). Statistical analyses illustrate a great failure of nodulation in Rh. japonicum uninoculated treatments. In case of inoculation with Rh. japonicum a clear enhancement of nodulation, symbiotic N2-fixation, plant growth.sbd.as indicated by leaf area, cell sap water potential, chlorophyll a, b and carotenoids content, plant dry matter and N-content, seed yield, filling (100-seed weight), and seed N-content.sbd.was detected as a result of soil inoculation with A. chroococcum. This enhancement effect is proved to be, not only due to fixed N that contributed by nonsymbiotic N2-fixation, but largely due to stimulation effects on nodulation and symbiotic N2-fixation processes. Inoculation by the two N2-fixers increased seed yield and N content/plant, seed N-percentage and 100-seed weight by 1.41, 13.2, 11.5 and 3.7%, respectively, than those obtained by inoculation with Rh. japonicum in addition to fertilization with 40 kg N/feddan.