The incidence ofAzotobacterand of nitrogen-fixing clostridia in some New Zealand soils

Abstract

The incidence of Azotobacter and of nitrogen-fixing clostridia was examined in 29 New Zealand soils under introduced pasture or native grasses, and also in some of the soils under crops or under spray-irrigation with dairy factory wastes. Azotobacter was recovered only from heavily manured soil from a market garden. Nitrogen-fixing clostridia were present in all soils. Numbers were lowest in dry, cool, or very acid soils (mean of hundreds per g), were lower in soils of coarse texture than in comparable ones of finer texture, and were greatest in moist soils of fine texture irrigated with dairy factory wastes (mean of millions per g). Ten soils from Australia and five from the Cook Islands were also examined. Azotobacter was recovered from half of them, and clostridia occurred in numbers similar to those in New Zealand soils with like rainfalls.