PARENT SESSION
Poster Session 11: Disturbance Ecology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Incorporation of plant residues into soil organic matter as impacted by grassland management practices in the North American Midwest.

Billings, Sharon^{*,1, 2}, Brewer, Courtney³, Foster, B¹, ¹ Department of Ecology and Evolutionary Biology, Lawrence, KS² Kansas Biological Survey, Lawrence, KS³ Norfolk State University, Norfolk, KS

ABSTRACT- Significant quantities of soil carbon (C) in North American prairies were released as CO₂ when this region was first plowed. As a result of this efflux of C from the ecosystem, these soils are often cited as having the potential to store large amounts of C. Fertilization of managed grasslands has been suggested as a means of promoting increased C storage in soils, but little is known about common grassland management techniques and their potential impact on soil C sequestration. Here, we examine how fertilization and annual haying impact soil C storage and accompanying organic matter transformations. We used a combination of aggregate size fractionation of soil organic matter (SOM), long-term soil incubations, ¹³C and ¹⁵N analyses, and litter quality indices to examine soils from a Kansan grassland. Fertilized soils possessed significantly more organic C than others (1.90±0.02 vs. 1.68±0.03%); this increase was predominantly harbored in the largest size fraction (212 to 2000 m). Incubation data and isotopic analyses suggest that fertilized soils experienced greater rates of organic matter turnover. Total C respired from fertilized soils was approximately 125% that from soils experiencing other treatments. The difference in ¹⁵N-enrichment between small and larger size fractions was greatest in fertilized plots, consistent with greater microbial activity in these soils. Though fertilization may promote greater C content in these soils, this study suggests that much of that SOM can be quickly returned to the atmosphere via a significant priming effect and accompanying microbial respiration. Plots that were both fertilized and hayed produced biomass with approximately 16% more lignin content than other treatments. This suggests that litter quality may be poorer under this management technique, which could result in reduced microbial activity in these soils. Work during the 2005 growing season will quantify soil CO₂ efflux in the field.

Key words: SOM fractionation, ¹³C, ¹⁵N, grassland management