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Title: Application of stable isotope analysis to quantify the retention of eroded carbon in grass filters at the North Appalachian experimental watersheds.

Author
item JACINTHE, P - INDIANA UNIV PURDUE UNIV
item LAL, R - OHIO STATE UNIVERSITY
item Owens, Lloyd

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2008
Publication Date: 12/9/2008
Citation: Jacinthe, P.A., Lal, R., Owens, L.B. 2009. Application of stable isotope analysis to quantify the retention of eroded carbon in grass filters at the North Appalachian experimental watersheds. Geoderma. 148(3-4):405-412.

Interpretive Summary: Carbon (C) and its distribution in the environment are central parts of the discussion of global climate change. There are many factors that impact C movement, distribution, and availability. Agricultural management practices are important to the sequestration, movement, and release of soil organic C (SOC). Water erosion from agricultural fields affects the redistribution and dynamics of SOC. Grass filter strips retain some of the sediment and eroded C. The purpose of this study was to determine amount and source of eroded C retained in grass filters. A method using a stable isotope of C was employed to assess the source of C. In a grass filter down slope from a mow-board plowed continuous corn field, SOC was nearly twice the levels measured in adjacent grassland. Corn-C accounted for up to 16% of the SOC found in the grass filter. Periodic delivery of nutrients in runoff may have enhanced increased biomass production and contributed to the greater level of SOC in the grass filters. In addition to demonstrating C retention and storage in grass filters, these results underscore the need to include in-situ biomass production in assessing SOC in erosion deposits and their importance to watershed C budgets. This work is important to other scientists working with C budgets, C storage, and C distribution.

Technical Abstract: The entrapment of eroded soil organic carbon (SOC) in grass filters could affect watershed C export, but the magnitude of the process is poorly quantified. In order to assess the retention of eroded C in these settings, SOC stock was measured in grass buffers receiving runoff from cropped watersheds under long-term (>20 y): chisel-till (CT) corn (Zea mays, L.)-soybean (Glycine max, L.) rotation, moldboard plowing (MP) continuous corn (CC), and no-till (NT) CC. Adjacent reference grasslands not affected by erosion were also sampled. In the CC watersheds, the d13C of bulk soil and soil separates was determined to gain insight into the source of SOC in the grass filters. When compared to NT, SOC stock in the MP watershed showed a corn-C deficit of 12.1 Mg C ha-1. Corn-C accounted for 2 to 16 % (mean: 4.8 Mg C ha-1) of the total SOC pool in the grass filter, and assuming water erosion as the main driver of C distribution, this corn-C gain translates into the retention of 40% of eroded C in the grass strip. Relative to the reference grassland, SOC stock in the grass filter was up to 30 Mg C ha-1 higher, an amount deemed too large to be attributed solely to retention of eroded C (export rate: 0.05-0.08 Mg C ha-1 y-1). Periodic delivery of nutrients may have enhanced biomass production and indirectly contributed to the observed SOC accrual in grass filters. Higher extractable P and higher C/N ratios at these locations support that interpretation. These results demonstrate the applicability of 13C isotope to trace SOC sources in buffers receiving runoff from areas supporting C4 vegetation. They also underscore the need to incorporate in-situ biomass production and burial processes in assessing the temporal evolution of SOC stocks in terrestrial deposits and the contribution of these landscape segments to watershed C budget.