XVI. Non-symbiotic nitrogen-fixing bacteria of two cultivated Soils

Summary

In Taupo and Cass soils under tussock grassland in New Zealand, the numbers of bacteria producing typical colonies of the nitrogen-fixing bacterium, Clostridium butyricum, were found to be similar in samples taken from the base of Festuca tussock plants and between well-spaced Festuca tussock plants. Total numbers of clostridia were a little higher in soil from the base of tussock plants. The numbers of Clostridium butyricum in these soils were increased by the growth of introduced pastures, after preliminary ploughing and the addition of fertilisers.

Azotobacter species were not detected in these soils under tussock grassland or introduced pastures or crops. Some other aerobic bacteria isolated from the cultivated soils were shown to be without appreciable nitrogen-fixing powers.