Nodulation, nutrient accumulation and yield of rainfed soybean in response to indigenous soybean-nodulating Bradyrhizobia in the Himalayan region of Kashmir-Pakistan

The use of efficient and effective nodulating Bradyrhizobia strains considered as an ecologically and environmentally sound management strategy for soybean production. A 2-yr (2009 and 2010) field experiment was conducted to evaluate the effects of seven indigenous Bradyrhizobium strains, one exotic TAL-102 and three N fertilizer rates, i.e., 25, 50 and 100 kg N ha-1 on the productivity and N2 fixation of rainfed soybean [Glycine max (L.) Merr.] grown in the Himalayan region of Rawalakot Azad Jammu and Kashmir (AJK), Pakistan. The experiment was conducted in a randomized complete block design with three replications. Bradyrhizobium inoculation accelerated plant growth by increasing shoot length (26-47%), root length (45-73%) and shoot dry weight (58-104%). Seed yield in the control was 861 kg ha-1 that significantly increased to 1450–2072 kg ha-1 with Bradyrhizobium strains. Seed yields under indigenous NR20 and NR22 strains was 24 and 28% higher than that recorded from the exotic TAL-102. Number of nodules, nodules dry weight and acetylene reduction assay with Bradyrhizobium strains were 55–123%, 94–178% and 38–103%, (respectively) higher than the non-inoculated control. The higher N rate (N100) depressed nodulation and N2 fixation. A significant variation in the symbiotic effectiveness and yield potential showed that inoculation response was site/strain specific. Two indigenous strains NR20 and NR22 were found highly efficient and displayed superiority over the exotic strain TAL-102. Multi-locational trials are required to check the suitability of these isolated isolates for other agro-climatic conditions before using as inoculants or bio-fertilizers.