Associative symbiosis of Azotobacter chroococcum and higher plants

The association between a selected strain of Azotobacter chroococcum and seven plants was investigated in water cultures under sterile conditions. Azotobacter population progressively increased in the nutrient solution and on the rhizoplane. Microbial propagation depends on the type of plant, being much higher in presence of wheat, followed by barley, maize, broad bean, and cotton, while in presence of fenugreek and lentil lower rates of multiplication were recorded. Inoculation increased the dry weight of plants by 5--12% and in length by 3--18% in addition to increased nitrogen content of plants and nutrient solution. Nitrogen balance showed no significant change in systems devoid of Azotobacter, but association between plants and the microorganism invariably showed positive results. The extent of N2-fixation depends on the type of plants; higher gains were recorded in presence of non-leguminous plants.