Effect of irrigation with municipal water or sewage effluent on the biology of soil cores

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Abstract
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 effluent from a biological filtration plant. Respiratory activity in the unamended soil was low, with respiratory quotient (R.Q.) less than 1. Addition of glucose produced about a four-fold increase in CO2 production and the R.Q. 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 most 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 effluent irrigated soils. All measurements showed greater differences among the different soils studied than between the two irrigation treatments.