Adilute solution of alkali (typically 1 Molar [M] NaOH) is placed in an open glass jar above the soil surface. A metal cylinder (usually 10 cm in diameter, an irrigation pipe will do) is installed well into the A horizon, carbon dioxide evolution is measured by absorption in the alkali solution for 24 hours, and then the CO2 amount absorbed is measured by backtitration of the excess alkali remaining. When expressed on a per unit area basis, the soil respiration data are comparable with literally hundreds of values from the literature about many different ecosystems.
Soil respiration is one of the most commonly used methods of determining metabolic activities of organisms in soil. As noted in Chapter 3, there is interest in determining the relative contributions of carbon dioxide evolved by the secondary consumers (microbes and fauna) as differentiated from that originating from respiring roots. For the purposes of this laboratory exercise, we will rely on comparisons of respiration from different ecosystems such as an arable field, forest, or grassland. Soil respiration, reflecting all of the biotic activity, is often measured to compare and contrast the side effects of chemicals such as pesticides and heavy metals. Soil respiration can be determined directly in the field. By measuring soil temperature and percentage of water in the soil, the relative contributions of these key abiotic variables can be calculated, which is useful in comparative ecosystem studies (e.g., Coleman, 1973). For more background on this method, consult also Alef and Nannipieri (1995).
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