Effectiveness of Nitrogen-Fixing Bacteria Rhodobacter sphaeroides in Soil–Plant Nitrogen and Rice Performance in Extremely Saline Acid Sulfate Soil over Two Consecutive Seasons

The overuse of chemical fertilizers under adverse conditions endangers the sustainability of agriculture. A biological approach should be investigated to address this issue. Therefore, this study aimed to detect the potency of purple non-sulfur bacteria that can fix nitrogen (N) (PNSB-fN) Rhodobacter sphaeroides in soil N fertility, plant N uptake, growth, and rice yield. In brief, an experiment was conducted to check whether the biofertilizer containing PNSB-fN strains can improve rice yield and soil fertility under a highly saline acidic condition. A randomized complete block design was used with four replicates on saline soil in An Bien-Kien Giang, Vietnam. The first factor was the N fertilizer level, i.e., (i) 100%, (ii) 75%, (iii) 50%, and (iv) 0%; the second factor was the PNSB-fN (R. sphaeroides), i.e., (i) the control, (ii) S01, (iii) S06, and (iv) combined S01–S06. In the results, supplying PNSB-fN increased NH4+ compared with the control, i.e., 104.7–112.0 mg NH4+ kg−1 compared with 94.0 mg NH4+ kg−1 in season 1 and 35.9–38.0 mg NH4+ kg−1 compared with 34.2 mg NH4+ kg−1 in season 2. Additionally, by supplying each PNSB-fN strain, the soil Na+ and plant Na in culm leaf and grain were decreased in comparison with those in treatments without PNSB-fN. The total N uptake was also enhanced by the PNSB-fN compared with the control. Moreover, supplying PNSB-fN improved the crop height, panicle length, panicle quantity pot−1, grain quantity panicle−1, filled spikelet rate, and grain yield compared with the control. Ultimately, in extremely saline soil, the mixture of PNSB-fN not only improved soil fertility and reduced soil salinity but also replaced 25% of chemical N fertilizer to ensure sustainable agriculture. This newly developed biofertilizer was potent in not only improving the rice and soil health in the locality but also performing the same under similar conditions around the globe.