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Published in Soil Sci Soc Am J 26:164-167 (1962)
© 1962 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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The Effect of Gamma Radiation on the Microbial Population of the Soil1

Hugh Popenoe and Charles F. Eno2

ABSTRACT

Arredondo fine sand was exposed to gamma radiation from a cobalt60 source at doses of 1, 4, 16, 32, 64, 256, 512, 1024, and 2048 kiloroentgens (kr.).

Percentage survival of fungi and bacteria decreased with each increase in radiation dose to < 4% at 1024 kr. Algae were not as drastically reduced as bacteria and fungi: some survived at 2048 kr. and greatest reduction occurred above 64 kr. A few nematodes remained in the soil 2 days after irradiation with 1024 kr., but none were recoverable from doses > 256 kr. after 14 and 28 days. The effects of lower doses were not resolvable.

Carbon dioxide evolution was initially reduced by irradiation of the soil. The reduction was generally inversely related to radiation dose except for the 64-kr. treatment. Later, all irradiated soils, except those which received doses > 256 kr., essentially equaled or exceeded the control in CO2 production. Soils treated with 512 and 1024 kr. produced only very small amounts of CO2 throughout the 23-day period; soil receiving 256 kr. later recovered completely. The soil irradiated by 64 kr. attained the highest daily production rate. Similar relationships for CO2 evolution occurred in an earlier study except for some shifts in time and magnitude.

Nitrate production in a 14-day period was progressively reduced by increasing doses of radiation. Recovery from 32 kr. or less occurred in 28 days; these soils produced at least 87% as much nitrate as the control during this period of time. Average production in 28 days at 64, 256, and 1024 kr. was 55, 7, and 3% of the control, respectively.

The production of sulfate from elemental sulfur was also affected by radiation in much the same manner as nitrate production, though radiation damage at doses less than 64 kr. were not readily apparent until the third week. Two populations, one more sensitive to radiation than the other, were probably involved in this reaction.

NOTES

1 Florida Agr. Exp. Sta. Journal Series No. 1258. Presented before Div. III, Soil Science Society of America, Dec. 6, 1960, at Chicago, Ill. The authors wish to express their appreciation to the Atomic Energy Commission for supporting this work in part, and to Dr. J. R. Christie, formerly Nematologist, Florida Agr. Exp. Sta., for making the nematode counts.

2 Assistant Soil Microbiologist and Associate Soil Microbiologist, respectively, Agr. Exp. Sta., University of Florida, Gainesville.

Received for publication April 27, 1961. Accepted for publication July 26, 1961.






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