SYMBIOTIC NITROGEN-FIXATION IN SOYBEAN AS INFLUENCED BY TIME OF INOCULATION

The influence of the time of inoculation with an indigenous Rhizobium strain on biological nitrogen fixation in soyabean was tested in a fie ld experiment in Greece, in an area extremely low in indigenous Rhizob ia effective on soyabean. Inoculation was either at sowing by seed ino culation or 30 days later with liquid solution. One nodulating and one non-nodulating variety of Glycine max (L.) Men., were used, while the contribution of the low indigenous Rhizobium population was measured with uninoculated plants of the nodulating variety. Nitrogen fertilize r labelled with N-15 enabled the nitrogen derived from fixation (% Ndf F), from fertilizer (% Ndff) and from the soil (% Ndfs) to be estimate d.The preadaptation of the inoculum to the ecological conditions of th e experimental area facilitated its survival with a very satisfactory effect on the amount of fixed nitrogen in all the inoculated treatment s (% NdfF 48%, N-2-fixed 115 kg ha(-1)). The time of inoculation had n o significant effect on N%, N-2-yield, % NdfF and N-2-fixed. On the ot her hand, all these parameters were considerably higher in the inocula ted treatments than in the uninoculated or the non-nodulating. Either method or time of inoculation can be equally well employed.