Fonte, Steven (Univ. of California, DavisDept. of Plant Sciences, University of California, Davis, CA, 95616; Phone: 530-754-7537; Email: sjfonte@ucdavis.edu)

 

Influence of Earthworm Activity and Cropping Systems on C Stabilization,

N Dynamics, and Greenhouse Gas Fluxes

 

S.J. Fonte *, A.Y. Kong, C. Van Kessel, P.F. Hendrix, J. Six

 

Earthworms are key regulators of soil structure and C turnover within many ecosystems, however, their influence on C and N fluxes in different cropping systems remains poorly understood.á By manipulating population densities of the endogeic earthworm Aporrectodea rosea in the field, this study examines the influence of earthworms on greenhouse gas fluxes and the incorporation of C and N into soil aggregates.á In situ microcosms were used to establish three levels of earthworm activity: no earthworms, background, and elevated (5 earthworms per microcosm).á These treatments were located within three corn-tomato systems: conventional, organic, and an intermediate low-input system (with legume cover crop and mineral nutrient inputs).á A 15N and 13C labeled cover crop was incorporated into the soil in the organic and low-input systems, while 15N labeled fertilizer was applied in the conventional system.á For all treatments, total C, 13C, total N and 15N were quantified in three aggregate size classes: macroaggregates (greater than 250 Ám), microaggregates (53 - 250 Ám) and the silt and clay fraction (less than 53 Ám).á In addition, microaggregates were isolated from within macroaggregates to determine the relative role of this fraction in stabilizing C.á Carbon dioxide and nitrous oxide were measured throughout the growing season using gas flux chambers in the field.á Preliminary analyses demonstrate a significant effect of management system on CO2 and N2O fluxes.á The highest flux for N2O (0.11 ÁMol N2O m-2 min-1) was observed in the conventional system in June of 2004, while the two cover crop systems exhibited the highest CO2 fluxes (mean flux of 803.2 ÁMol m-2 min-1) on the same sampling date