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Soil algal productivity and biomass were monitored in a conventional tillage agricultural system from December 1981 through December 1982. Productivity was based on the fixation rate of radiolabeled carbon dioxide. Biomass estimates (cell number and volume) were based on cell counts radiolabeled carbon dioxide. Biomass estimates (cell number and volume) were based on cell counts and measurements done with epifluoroscence microscopy. Algal productivity values (measured as carbon fixation) ranged from 0 to 76 mg°m—2°h—1, values for cell number ranged from 5.85 x 108 to 5.19 x 1010 cells/m2 and the volume of cells was between 34.8 and 7540 mm3/m2. Regression analysis indicates that algal productivity was most closely correlated with the product of cell number and light intensity, while a number of cells per square metre was most closely correlated with the product of temperature and moisture. The logarithm of the average volume per cell was inversely correlated with soil moisture and temperature. The percentage of algae present as aggregates was proportional to moisture and the square of temperature. Total annual productivity (as carbon) was estimated to be 39 g/m2.

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