The effect of inoculation with Azospirillum brasilense on growth, water status and yield of dryland sorghum (cv. RS 610 and cv. H-226) growing on stored soil moisture was examined in three field experiments conducted during the years 1983–5.
Plants were sampled at regular intervals, and the following characteristics were measured: dry-matter accumulation, leaf area, grain yield, percentage nitrogen and phosphorus in leaves, leaf water potential, canopy temperature, transpiration, stomatal conductance and soil water depletion.
Inoculation led to an average increase of 19% in total stover dry-matter yield, as a result of higher rates of dry-matter accumulation during the early stages of growth. Azospirillum inoculation caused a 15–18% increase in grain yield in all three experiments. This increase was associated with a greater number of seeds per panicle.
The water regime of sorghum plants was improved by inoculation, as seen in their higher leaf water potential, lower canopy temperatures and greater stomatal conductance and transpiration. Total extraction of soil moisture by inoculated plants was greater (by about 15%) and occurred from deeper soil layers, compared with non-inoculated controls.
These findings indicate that inoculation with Azospirillum can lead to yield increases in dryland grain sorghum, primarily through improved utilization of soil moisture.