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Bacterial Effects on Hydraulic Conductivity of Soils¹

ABSTRACT

Laboratory experiments were performed to determine the relationship between bacterial pore clogging and soil hydraulic conductivity. When soils were submerged and hydraulic conductivity was plotted against time, the conductivity decreased and eventually stabilized at a constant value. The time required, the stable value, and the coefficient of variability were all influenced by the treatment applied to the soil. Sterile soils had the highest hydraulic conductivity and lowest C. V. of all treatments. The lowest hydraulic conductivity resulted from the addition of both a C and a N source. Continuous submergence and wetting and drying cycles were compared in their effects on hydraulic conductivity. A specific portion of the total biological activity (as determined by the acid phosphatase assay) and a selective bacterial population (accounted for by the medium used) were significantly and negatively correlated with hydraulic conductivity. As the bacterial population and phosphatase activity increased, the hydraulic conductivity decreased. The decrease in hydraulic conductivity under prolonged periods was primarily due to the excretion of metabolic products produced by bacteria within the soil pores.

¹ Journal Paper No. 9081 of the Iowa Agric. Home Econ. Exp. Stn., Ames. Project 2134. Presented before Div. S-3, Soil Sci. Soc. Am., Houston, Texas, 29 Nov. 1976.

² Research Assistant, Professor, and Associate Professor, respectively, Department of Agronomy, Iowa State Univ., Ames, IA 50011.

Received for publication March 13, 1978. Accepted for publication November 15, 1978.