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Soil Aggregate Stabilization by the Indigenous Microflora as Affected by Temperature¹

ABSTRACT

The water-stability of sucrose-amended aggregates of Waupun silt loam incubated at 15, 25, and 35C, and the aggregate-stabilizing characteristics of microorganisms isolated from these aggregates were evaluated. Aggregate water-stability determined by wet-sieving was expressed as the percentage of soil material bound into water-stable aggregates 0.5 to 1 mm, 1 to 2 mm, and > 2 mm in size. Microbial development was investigated by microscopic and dilution plate techniques.

Fungi isolated from the aggregates differed in their ability to effect aggregate stabilization in the presence and absence of sucrose. Stabil zation by effective fungi was a function mainly of the binding of soil particles into > 2-mm water-stable aggregates and was related closely to the onset and subsequent development of macroscopic mycelia on the aggregates. Stabilization of aggregates by sporeforming bacteria involved the production of a high percentage of <2-mm aggregates, especially in the early stages of incubation. Bacterial stabilization was initiated earlier but was maintained for a shorter time as incubation temperature increased from 15 to 35C; maximum aggregate stability effected at 15 and 25C was almost twice that reached at 35C.

Maximum stabilization by the indigenous microflora occurred within 4 days at all 3 temperatures; appreciable stability was maintained for 84, 14, and 4 days at 15, 25, and 35C, respectively. Bacteria were primarily responsible for the initial stabilization of aggregates incubated at 15 and 25C and contributed to the initial stabilization of aggregates incubated at 35C. The fungal species involved in aggregate stabilization varied with temperature.

¹ Contribution from the Departments of Soils and Bacteriology, University of Wisconsin, Madison. Published with approval of the Director, Wisconsin Agr. Exp. Sta., Madison, Wisconsin under Hatch Project 722. Presented before Div. S-3, Soil Science Society of America, Nov. 1964, at Denver, Colo.

² Assistant Professor and Associate Professor of Soils and Professor of Bacteriology, respectively.

Received for publication July 28, 1965. Accepted for publication October 5, 1965.