Ham, Jay (Kansas State University, Dept. of Agronomy, Throckmorton Hall, Manhattan, KS, 66506; Phone: 785-532-6119; Email: jayham@ksu.edu)

Automated Chambers for Measuring Soil and Canopy Respiration From Rangeland

J.M. Ham *, E.J. Benson, F.W. Caldwell, C.E. Owensby

A multiplexed automated chamber system was developed to monitor ecosystem respiration (R) from tallgrass prairie near Manhattan, Kansas. Chambers were deployed for one year in the source areas of eddy covariance towers in grazed and ungrazed pastures. The main purpose of the chambers was to improve long-term estimates of nocturnal and dormant season CO₂ losses. Chamber data were used to evaluate the performance of the eddy covariance systems at night when tower-based net carbon exchange measurements should be equal to R. Rectangular opaque chambers (0.85 m x 0.85 m x 0.25 m) were automatically deployed at 1 or 2 hourly intervals using four-arm linkage and 12V-winch. Flux was determined from CO₂ vs. time curves using a non-steady-state measurement. When idle, the chambers rested on a parking platform north of the sample plot; thus, the plot microclimate was not affected. Surface fluxes followed strong diurnal patterns that were correlated with air temperature. Predawn fluxes were often 45 % less than daytime maximums. During June 2004, the peak of the growing season, daily CO₂ fluxes were 33.6 and 28.9 g/m²/d from the ungrazed and grazed plots, respectively. Grazing caused a 12 to 16 % reduction in respiration. Results also will address the best ways to calculate chamber-based fluxes from the CO₂ vs. time curves and (2) optimal methods for sampling gap filling.