Use of Nitrogen Fixing Purple Nonsulfur Bacteria to Produce Available Nitrogen for Rice (Oryza sativa L.) Cultivated in Saline Acidic Soil

This research aimed to select N2-fixation purple nonsulfur bacteria (PNSB) from saline acidic soils (SAS) in rice-shrimp system to enhance rice growth and yield. Two PNSB with highest nitrogen-releasing strains Luteovulum sphaeroides S01 and S06 were used, and the SAS was collected from Hong Dan and Thanh Phu districts. The 4 x 4 factorial experiment was carried out in a completely randomized block design, including a main factor as the liquid biofertilizers and the minor factor as the N fertilizer levels, with four replicates in a greenhouse. Both individual and mixed PNSB liquid biofertilizers significantly increased pH value and NH4+ content and reduced the exchangeable Na+ in both SAS sites. This led to 24.8-113.2% higher N uptake in rice and 6.48-30.5% lower Na accumulation in straw and 16.3-47.6% Na in grain. These results were considered as an evidence to improve rice grain yield by 27.5-56.6%. The L. sphaeroides S01 and S06 was greatly suitable for using as a biofertilizer for rice under saline acidic conditions.