Presence of nitrogen in the medium inhibits the reduction of nitrogen by rhizobia this can be categorized in feedback inhibition reaction, In general pulse plants can supply 80% of their request, and thus any excess supply of nitrogen is accompanied with a reduction in nitrogen reductase   

Mr. Antoun

I inoculated overnight culture of Rhizobia 5ml per plant.

I sterilized seed with 2% NaOCl for 5 min and 70% ethanol for 45 sec finally 6 times with ddH2O. All of my samples did not induced nodules on Soybean plants. Yes the color of nodules was yellow and white and size was more or less 2-3 mm in diameter.

I got dry weight of control 0.45 gm where nodulated plants yielded 0.17, 0.25, 0.37, 0.47, 0.55 gm etc.

I only supplied 15 ml 1X Fahraeus N-free medium and 10ml ddH2O within a month before harvest.

The plants were cultivated at 1% agar in a glass house. I did not get fungal contamination in majority of plants.     

You got strange result! It should be some contaminations. You should check if your bacterial strains are effective or ineffective. Because rhizobia can fix nitrogen from the air. You should mention also number of rhizobia /seed?

I think Your problem in sterilization high NaOCl concentration and duration besides the Ethanol concentration....