AGRONOMIC APPLICATIONS OF AZOSPIRILLUM - AN EVALUATION OF 20 YEARS WORLDWIDE FIELD INOCULATION

By evaluating worldwide data accumulated over the past 20 years on field inoculation experiments with Azospirillum, it can be concluded that these bacteria are capable of promoting the yield of agriculturally-important crops in different soils and climatic regions. Various strains of A. brasilense and A, lipoferum have been used to inoculate cultivars of different species of plants. It is however difficult to accurately estimate the percentage of success due to Azospirillum inoculation. The data indicates 60-70% occurrence of success with statistically significant increases in yield of the order of 5-30%. Successful inoculation experiments appear to be those in which the researchers have paid special attention to the optimal number of cells of Azospirillum in the inoculant, using inoculation methods where the optimal number of cells remained viable and available to colonize the roots. Furthermore, experiments taking into consideration the potentialities and limitations of this technology have been better able to explain successes and failures. The different formulations (analogous to those of rhizobia) of the genus Arospirillum, irrespective of their form of application and their mode of action on the plant, are indeed inoculants. The term biofertilizer is not appropriate as it does not replace fertilizer but improves their utilization. We very strongly suggest the implementation by regulatory authorities of quality control on commercial Arospirillum inoculants.