Salinity Resistance of Azotobacter Isolated from Saline Soil in West Java

The important barrier for food crop production in saline soils is high electrical conductivity as well as low nitrogen availability. Biofertilization through the application of a nonsymbiotic nitrogen-fixing rhizobacterium which is resistant to the saline condition is one of the ways to increase nitrogen uptake in such soil. The objectives of this experiment were to evaluate the resistance of Azotobacter for sodium chloride and their effect to enhance the early growth of tomato seedling. Azotobacter was isolated in Ashby’s medium from paddy soil with the electrical conductivity of 4 dS m−1. Sensitivity test to saline condition was conducted in sterile Ashby liquid medium enriched with 0.85%, 1.7%, and 3.4% of sodium chloride for three isolates with higher N-fixing capacity. For pot trial, tomato seedling was grown in saline soil and inoculated with single strain bacterial liquid culture. The pot experiment was setup in split-plot design to test the combination treatment of two most sodium-resistant Azotobacter isolates and their concentration. The results showed that Azotobacter isolates S2 and K4 were more resistant to 3.4% sodium chloride although their generation time was slightly higher. In the pot trial, shoot height of a 4-week-old tomato seedling increased after Azotobacter S2 and K4 mixed inoculation. Azotobacter inoculation increased leaf number and root’s dry weight of tomato. The results suggested that saline-resistant Azotobacter has plant growth-promoting activity.