FLUCTUATIONS IN NUMBERS OF BACTERIA IN SOIL

Abstract

Comprehensive studies on the relation of moisture, temperature, and time to the numbers of bacteria in a fallow plot were carried on over a period of 15 weeks during the summer of 1939. The data involved represent: moisture—percentages of dry weights of samples; temperature—averages of air temperature readings for three days preceding samplings; time—numbers of days from the beginning of the experiment to dates of sampling; numbers of bacteria—plate count determinations from the following:On each of 6 dates 5 composite samples, with 48 plates from each.On each of 6 dates 9 composite samples, with 27 plates from each.On each of 10 dates 12 composite samples, with 27 plates from each.On the basis of linear regression, bacteria in millions and moisture in percentage give a significant correlation for between day samples. The same is true for samples plated on the same day.The application of multiple regression of average numbers of bacteria in the samples handled at each date on average moisture in percentage, temperature in degrees F. and time in days shows that these environmental factors account for most of the variation in numbers of bacteria in the plot during the period of this study.The correlation between numbers of bacteria and moisture in the samples on different dates was found to be logarithmic. This relation becomes more nearly linear when the correlation is carried out on the numbers of bacteria adjusted for the factor associated with time.