Biological studies of some tussock‐grassland soils

Summary Three New Zealand tussock‐grassland soils, viz Taupo soil near Waiouru, Tekoa soil near Bealey, and Omarama soil near Alexandra, have been found to contain the nitrogen‐fixing anaerobic bacterium Clostridium butyricum , in numbers comparable with those reported in soils in other temperate countries. There is no marked variation in the numbers of this Clostridium in the different soils and there is no consistent difference between samples taken from the base of Festuca tussock plants or between well‐spaced Festuca tussock plants. Azotobacter spp. were not detected. Other aerobic bacteria and yeasts isolated from the soils or from leaves of Festuca tussock plants have been found to be without appreciable nitrogen‐fixing powers. It is suggested that the contribution of non‐symbiotic bacteria to the nitrogen reserves of these soils is small. Other agencies which may be adding to the soils nitrogen content are briefly considered.