Studies on the aerobic bacterial flora of a New Zealand tussock grassland soil

Abstract

The work described herein was best divided into 4 rather distinct parts. All are concerned with the aerobic bacterial flora of a single New Zealand grassland soil whose characteristics are described. The 4 parts deal respectively with the characterisation of the aerobic heterotrophic bacterial flora, the activity this flora as measured by a number of different techniques, nitrification and sulphur oxidation.

Until very recently no information has been available on the bacteria inhabiting New Zealand soils and none on their activity in soil. It has been pointed out that little is known of the relative ability of many common bacteria to grow in soil or of their relative function and importance in soil metabolism. The studies planned provided an opportunity for examining some of these points in a virgin soil whose history and recent treatment have been well documented. It was hoped that such studies, while of general interest, might also be of value in planning further work to help explain some of the fertility problems in the vast areas of virgin grassland soils in New Zealand.

New Zealand soils are for most developmental purposes deficient in sulphur. In the development of remote and inaccessible soils, air application of chemical fertilizers is the only means possible. Bulk of materials is an important economic consideration in these operations and elemental sulphur, provided it is readily oxidized to its plant-available form sulphate, is the application of choice. Field studies in New Zealand have shown that elemental sulphur becomes available to plants very slowly. Consequently a study of sulphur oxidation by soil bacteria was indicated in this work.

Finally, the status of the nitrifying bacteria was studied because of frequent reports in the literature that, in grasslands, these organisms function at a very low efficiency. Because this work constituted something of a pioneering venture in New Zealand, the author was requested to apply a variety of techniques to the study of the soil microflora. It was hoped that an evaluation of techniques in this work would lead to the establishment of a continuing programme in soil microbiology at Lincoln College in co-operation with other soil scientists.