Symbiotic Nitrogen Fixation in Soyabean as Influenced by Time of Inoculation

Abstract

ABSTRACT The influence of the time of inoculation with an indigenous Rhizobium strain on biological nitrogen fixation in soyabean was tested in a field experiment in Greece, in an area extremely low in indigenous Rhizobia effective on soyabean. Inoculation was either at sowing by seed inoculation or 30 days later with liquid solution. One nodulating and one non-nodulating variety of Glycine max (L.) Merr., were used, while the contribution of the low indigenous Rhizobium population was measured with uninoculated plants of the nodulating variety. Nitrogen fertilizer labelled with 15N enabled the nitrogen derived from fixation (% NdfF), from fertilizer (% Ndff) and from the soil (% Ndfs) to be estimated. The preadaptation of the inoculum to the ecological conditions of the experimental area facilitated its survival with a very satisfactory effect on the amount of fixed nitrogen in all the inoculated treatments (% NdfF 48%, N2-fixed 115 kg ha−1). The time of inoculation had no significant effect on N%, N2-yield, % NdfF and N2-fixed. On the other hand, all these parameters were considerably higher in the inoculated treatments than in the uninoculated or the non- nodulating. Either method or time of inoculation can be equally well employed.