Soil Carbon Dioxide Respiration in Switchgrass Fields: Assessing Annual, Seasonal and Daily Flux Patterns

Quantifications of annual soil respiration in switchgrass systems are limited to the growing season or coarse-scale temporal sampling. This study evaluates daily and seasonal soil CO2 respiration in switchgrass croplands. Hourly measurements during a 12-month period were taken for soil CO2 flux, soil temperature, and soil moisture. Although both soil temperature and moisture were positively correlated with soil CO2 flux rates, soil temperature was the primary driver of soil respiration. During winter, lower soil temperatures corresponded with significant decreases in average daily CO2 flux rates, however, CO2 pulses associated with precipitation events increased flux rates up to three times the seasonal daily average. Soil temperature influenced both daily and seasonal flux patterns where the highest flux rates, up to 31.0 kg CO2 ha(-1) h(-1), were observed during the warmest hours of the day (13:00 to 15:00) and during the warmest season (Summer). Summer and Spring emissions combined accounted for 80.1% of annual flux, indicating that exclusion of non-growing season time periods may result in an underestimation of total annual CO2 efflux. Our results indicate that inclusion of the non-growing season and a fine-resolution temporal sampling approach provides more accurate quantifications of total annual CO2 emissions in switchgrass croplands.