The measurement of soil carbon dioxide respiration is a means to gauge biological soil fertility. Test methods for respiration employed in the laboratory vary somewhat, and to date the equipment and labor required have somewhat limited more widespread adoption of such methodologies. The purpose of this research is to compare the results of measured soil CO 2 respiration using three methods: (1) titration method; (2) infrared gas analysis (IRGA); and (3) the Solvita gel system for soil CO 2 analysis. We acquired 36 soil samples from across the USA for comparison, which ranged in pH from 4.5 to 8.5, organic C from 0.8 to 4.6% and the clay content from 6 to 62%. All three methods were highly correlated with each other after 24-h of incubation (titration and Solvita r 2 = 0.82, respirometer and Solvita r 2 = 0.79 and titration versus respirometer r 2 = 0.95). The 24-h (1-day) CO 2 release from all three methods was also highly correlated to both basal soil respiration (7-28 days) and cumulative 28-day CO 2 respiration. An additional 24 soil samples were acquired and added to the original 36, for a total of 60 soil samples. These samples were used for calibration of the Solvita gel digital color reader results using CO 2 -titration results and regression analysis. Regression analysis resulted in the equation y = 20.6 * (Solvita number) -16.5 with an r 2 of 0.83. The data suggest that the Solvita gel system for soil CO 2 analysis could be a simple and easily used method to quantify soil microbial activity. Applications may also exist for the gel system for in situ measurements in surface gas chambers. Once standardized soil sampling and laboratory analysis protocols are established, the Solvita method could be easily adapted to commercial soil testing labs as an index of soil microbial activity.

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Samples of active and cured compost from across the U.S. are examined for volatile organic acids (VOA) in relation to other microbiological and chemical properties. VOA are considered important because they reflect temporal microbiological properties of active and cured compost that influence the potential for compost to become odorous and phytotoxic. Data collected from 712 compost samples reveals a wide range of concentration for VOA between 75 and 51,474 ppm (dry basis) with a mean concentration of 4,385 ppm. To understand the variability of VOA, technology and site-specific testing data are needed. The results underscore concern for phytotoxicity and odor release potential, as 15 percent of samples exceeded 10,000 ppm and 2.5 percent exceeded 25,000 ppm VOA. Data and methodologies presented are viewed as useful to better understand relationships between compost biological activities and production of malodorous and phytotoxic VOA.