RESPONSES OF SOIL RESPIRATION TO CLIPPING AND GRAZING IN A TALLGRASS PRAIRIE

Soil-surface CO2 flux (F-s) is an important component in prairie C bud gets. Although grazing Is common in grasslands, its effects on F-s hav e not been well documented. Three clipping treatments: (i) early-seaso n clipping (EC); (ii) full-season clipping (FC); and (iii) no clipping (NC); which represented two grazing strategies and a control, were ap plied to plots in a tallgrass prairie in northeastern Kansas, USA. Mea surements of F-s were made with a portable gas-exchange system at week ly to monthly intervals for 1 yr. Concurrent measurements of soil temp erature and volumetric soil water content at 0.1 m were obtained with dual-probe heat-rapacity sensors. Measurements of F-s also were obtain ed in grazed pastures. F-s ranged annually from 8.8 x 10(-3) mg m(-2) s(-1) during the winter to 0.51 mg m(-2) s(-1) during the summer, foll owing the patterns of soil temperature and canopy growth and phenology . Clipping typically reduced F-s 21 to 49% by the second day after cli pping despite higher soil temperatures in clipped plots. Cumulative an nual F-s were 4.94 4.04, and 4.11 kg m(-2) yr(-1) in NC, EC, and FC tr eatments, respectively; thus, clipping reduced annual F-s by 17.5%. Di fferences in F-s between EC and FC were minimal, suggesting that diffe rent grazing strategies had little additional impact on annual F-s. Da ily F-s in grazed pastures was 20 to 37% less than F-s in ungrazed pas tures. Results suggest that grazing moderates F-s during the growing s eason by reducing canopy photosynthesis and slowing translocation of c arbon to the rhizosphere.