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The persistence of Bradyrhizobium sp. (Cajanus) CC 1021 inoculated into soil under field conditions was determined by a most probable number (MPN) technique. Survival was very poor and the strain did not persist into the next cropping season. The soil temperature in the top 15cm of soil remained at 35°C or above during the cropping season of pigeonpea. In general the temperature in the top 5cm layer was higher than the ambient, but at 15cm depth it was almost equal. The maximum temperatures recorded at 5cm depth in the years 1984 and 1985 were 52.5 and 45°C, respectively during June and May. Soil moisture fluctuated widely between 2 and 15.5%.

After the onset of rain, there was an increase in the number of resident rhizobia in the soil, but following drying the number fell. A downward movement of inoculant rhizobia was observed.