INTERACTIVE EFFECT OF NITROGEN FERTILIZATION AND RHIZOBIUM INOCULATION ON NODULATION AND YIELD OF SOYBEAN (Glycine max L. Merrill)

A field experiment was conducted for two consecutive seasons (2009/10 and 2010/11) in the Demonstration Farm of the Faculty of Agriculture at Shambat-Sudan, to study the interactive effect of nitrogen fertilization and rhizobium inoculation on nodulation and yield of soybean (Glycine max [L.] Merrill) plants. The experiment was laid out in a randomized complete block design with four replications. The treatments consist of increasing doses of nitrogen (0, 40 and 80 kg ha -1 urea) and one strain of rhizobium. The seeds of cultivar Giza 22 were either uninoculated or inoculated with Rhizobium japonicum strain TAL 110 before sowing. The results showed that nodules were only formed on inoculated plants and their number varied with the level of nitrogen fertilizer. The number of nodules and their dry weight per plant declined as the rate of nitrogen application increased. Inoculated or fertilized plants significantly increased seed yield relative to uninoculated non-fertilized control plants by 83% and 89%, respectively. However; the high dose of nitrogen fertilizer (80 Kg ha -1 ) depressed the positive effect of inoculum on seed yield. The high seed yield was associated with significantly higher number of pods per plant and number of seeds per pod. Rhizobium inoculated seeds exhibited increased protein content than that of control (63.3 vs 59.9) but with no effect on seed oil content. Application of small N-fertilizer (40 kg ha -1 ) in combination with rhizobial inoculation seemed to be an appropriate cultivation practice for soybean production under Sudan condition.