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Locus of Urease Activity in Soil¹

ABSTRACT

A model is proposed to determine the location of active urease in soil; that is, whether the urease was associated directly with soil microorganisms or free from microorganisms and adsorbed on the soil colloids. An indirect approach was used which consisted of making periodic measurements of urease activity during a period of time when the microbial population was undergoing change. Multiple regression analysis was applied to the data to determine the relationship between urease activity and microbial population. Under steady state conditions, 79–89% of the urease activity of the soil examined was due to urease adsorbed on soil colloids. An increase in microbial population reduced this percent temporarily until a new steady state was reached. Addition of a small amount of urea (13 ppm of urea-N) to the soil induced microorganisms to produce more urease.

¹ Contribution from the Department of Agronomy, University of Illinois at Urbana-Champaign. Presented before Div. S-3, Soil Science Society of America, Nov. 13, 1968, at New Orleans, La. The results are contained in a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree.

² Instructor and Professor of Soil Fertility, respectively, University of Illinois at Urbana-Champaign.

Received for publication March 19, 1969. Accepted for publication August 6, 1969.