THE EFFECT OF PARTIAL STERILIZATION OF FIELD SOILS BY CHEMICALS UPON DIFFERENTIAL MICROBIAL COUNTS, CO2 ACTIVITY, AND RATES OF ORGANIC MATTER DECOMPOSITION

Abstract

Varying dosage rates of calcium hypochlorite, mercuric chloride, and sodium propionate were used as partial sterilization agents in field and greenhouse trials to determine the effect on soil biological activity, and thereby, organic matter decomposition rates. Application of the chemicals often resulted in the initial stimulation of respiration rates. In greenhouse and field trials this stimulation was most commonly associated with the application of sodium propionate. Fungal counts decreased and bacterial counts increased when this chemical was used. Within 4 weeks after treatment, all rates of application of the various chemicals depressed soil CO2 evolution. Thirteen months after treatment, plots treated with 100 lb of mercuric chloride per acre had one quarter as many actinomycetes and total microbes, and one third as many fungi, as did the control plots. Respiration was also considerably lower. Calcium hypochlorite treated plots retained reduced total counts and sodium propionate reduced fungal counts. Respiration in these last plots was not depressed.The changes in organic matter decomposition due to chemical treatments were not statistically significant in the greenhouse or field studies.General lack of correlation between the three measures of biological activity used in this study indicate the necessity for the further development of methods for measuring the population of microorganisms in soil.