Microbial populations and respiratory activity are reported for topsoils (0-10 cm) of 15 cm diameter cores (depth 50 cm) of 10 pasture soils representative of soils of North Island, New Zealand, after 15 months' irrigation with either municipal tapwater or unchlorinated sewage effiuent from a biological filtration plant. Respiratory activity in the unamended soil was low, with respiratory quotient (R.O.) less than 1. Addition of glucose produced about a four-fold increase in CO? production and the R.O. rose to 1. Total microbial populations were similar. There were few bacterial spores but more actinomycetes. Gram-negative bacteria comprised only a small proportion of the population. Coliform counts, both total and faecal, were low. A wide range of organisms were present; the moat numerous, other than bacteria and fungi, were flagellates, amoebae, and solitary green algae. Representatives of the fauna found in the filtration plant were recovered from the effiuent irrigated soils. All measurements showed greater oifferences among the different soils studied than between the two irrigation treatments.

Survival of faecal coliforms and faecal streptococci, with special emphasis on Streptococcus bovis, in soil and drainage water held at 50, 100, 150, and 20 0 e under laboratory conditions was studied by membrane filtration techniques. In drainage water number of coli forms I'ad increased by more than 100% after 48 h at all temperatures, but number of faecal streptococci had fallen, particularly at 20 0 e. at which the number had dropped by 80%. There was no clear pattern of coliform survival in eillucnt-irrigated soil; the general trend was a decrease at 5°, 100, and 15°e up to 4 days, but an increase of 30% at 20 o e. Similarly, faecal streptococci had decreased by the fourth day at 5°, 10°, and 15°e and by 300% at ~Ooe. S. bovis represented 60% of all isolates from the drainage water and only 6% from the eilluent-irrigated soil. Sixty percent of the S. bovis isolates survived for 7 days at 10°c in the drainage water. The low level of S. bovis recorded in the soil may be due to the unsuitability of the membrane filtration technique for soil samples. An alternative method should be developed as soon as possible.

The attachment of Escherichia coli and Streptococcus bovis of bovine faecal origin to soil clay particles has been examined using scanning electron microscopy. Both organisms produce extracellular polymers through which the cells form bridges to clay surfaces. Differences in the extent of cell‐to‐particle bridging between E. coli‐and S. bovis‐soil complexes are explained in terms of the charge characteristics of the cells and the properties of the exopolymers.

SUMMARYThe effect of flooding was studied on eight hasidiomycete fungi growing on pieces of wood which were buried and flooded for 12 weeks. None of tbe fungi was re-isolated from the flooded site, and the cause of the phenomenon was investigated, using a hioassay with Peniophora sacrata as the test fungus. When four Bacillus spp. and three Clostridium spp. from this site were added together to McCartney bottles containing soil and P. sacrata, and then fiooded, the fungus was killed, hut not when single hacterial species were used. This potential was present in 24 of 32 soils in the southwest Pacific.

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