Wednesday, August 4, 2010
Exhibit Hall A, David L Lawrence Convention Center
Background/Question/Methods
Carbon and nitrogen retention processes within agricultural ecosystems are currently of prime interest due to environmental policies impacting agricultural producers. Many studies have focused on contrasting tillage systems and have not included a wide range of land uses despite acknowledgment that land management practices are known to alter pools of carbon (C) and nitrogen (N) within mineral soils. The central Pennsylvania Ridge and Valley physiographic province is an ideal study region due to diverse land use practices and to its hydrologic connection to the Chesapeake Bay. Our study addresses two main questions: How does land use affect pool sizes of mineralizable C and N, and how does land use alter soil aggregation processes? We investigate total and mineralizable pool sizes for C and N, and attempt to correlate aggregate fractions with C and N mineralization across land use types. We located replicated patches of 6 land-use types on a common soil type. Land use types included conventional and no-till agriculture, pasture, unfertilized grass, urban turf and forest. Land use continuity was confirmed by examining historical aerial photos. On surface mineral soils we quantified C and N content, potentially mineralizable pool sizes, and the distribution of C and N among soil aggregate fractions. Results/Conclusions Land-use types differed significantly in total soil N, potentially mineralizable N and total soil C, but not in mineralizable C. Total soil N was similar across forest, unfertilized grass, pasture and urban sites, ranging from 0.19-0.26%N, but conventional tillage (0.14%N) was significantly lower than untilled sites. Urban sites showed significantly higher N mineralization (25.8 mg kg-1) than forest and unfertilized grass sites (15.5, 12.3 mg kg-1). Conventional tillage sites (1.25%C) stored significantly less total soil C than sites not subject to tillage (3.01-2.43%C); no-till sites (1.94%C) stored significantly less C than forest (3.01%C). Pasture and unfertilized grass total C and N values were intermediate between those of forest and agricultural sites consistent with management intensity. Distribution of C and N within aggregate fractions in conventional and no-till agroecosystems and urban sites shows significantly greater storage of C and N in free and macroaggregate-bound silt and clay and microaggregates within macroaggregates in urban sites over conventional tillage sites; no differences in free microaggregates were observed across the three land-use types. This study, while comparative in nature, lays the groundwork for further research on aggregation processes and C and N retention and release within different land use types.
