Sterilization of Soil by Irradiation and Some Further Observations on Soil Enzyme Activity

Abstract

Abstract As an introduction to the study of radiation‐sterilized soil as a medium for microbial and plant growth, survival curves for microorganisms have been obtained with 5 and 9 Mev. electrons, hard X‐ray and gamma radiation. For a given soil, bacterial survival curves with these radiations are almost superimposable, but they differ among soils. Bacterial numbers in soils approach zero at 2 Mrep. doses, but 4 Mrep. doses are necessary to insure complete sterility for larger soil volumes. Soil sterilized by radiation still manifests enzyme activity (phosphatase, urease) in the presence of suitable substrates. If this is a general situation, studies of the uptake of some organic nutrients from sterile soil by sterile root systems will not be free from the problem of hydrolysis in situ . Sterilized soil is not toxic toward tomato plants nor does it provide extra nutrient to the plants as a result of radiation. It does, therefore, provide the plant physiologist with a medium for the study of uptake of inorganic nutrients by sterile plants which possesses all the purely chemical and structural features of natural soil.