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Title: TRANSPORT OF LABILE CARBON IN RUNOFF AS AFFECTED BY LAND-USE AND RAINFALL CHARACTERISTICS

Author
item JACINTHE, P - OHIO STATE UNIV.
item LAL, R - OHIO STATE UNIV.
item Owens, Lloyd
item Hothem, Daniel

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2003
Publication Date: 2/25/2004
Citation: Jacinthe, P.A., Lal, R., Owens, L.B., Hothem, D.L. 2004. Transport of labile carbon in runoff as affected by land-use and rainfall characteristics. Soil & Tillage Research. 77:111-123.

Interpretive Summary: Soil organic matter and the carbon (C) cycle are part of the current discussion on factors that impact carbon sequestration and global climate change. Some soil C leaves a field when erosion occurs, and large areas of the world are impacted by erosion. This study investigates the amount of C lost with erosion from 5 different management practices, notill (NT), chisel till (CT), disk till low input (DT-LI), pasture, and forest. The DT-LI uses manure applications and legume cover crops to partly supply the N needed when corn is grown, and it uses cultivation to reduce the use of herbicides. Runoff and sediment were measured and sampled with each storm. Annual soil and organic C losses from the DT-LI (3.5 T/Ac and 102 lb/Ac, respectively) were at least twice as great as from the other practices. But the rainfall storm class, based on intensity and energy, was a better indicator of sediment of C concentration than management practice. Sediment collected during low intensity storms (usually in fall/winter) contained more organic (3.7% C) than sediment collected during high intensity summer storms (2.25% C). The low intensity storms seemed to have more selective detachment of materials with higher C concentrations. However, even the low intensity storms had greater C concentrations, the infrequent but high intensity summer storms would carry much more sediment and carbon. Thus the high intensity storms could determine the overall impact of erosion on soil C movement. This information will be useful to other scientists as well as to producers and agricultural advisors.

Technical Abstract: The immobilization of organic carbon (C) by water erosion occurs over large areas of the terrestrial biosphere and thus could impact the global C cycle. The magnitude and direction of that impact remain uncertain given a lack of data regarding the fates of eroded C. A study was conducted to monitor total organic C and mineralizable C (MinC) in eroded materials from watersheds under no till (NT), chisel till (CT), disk till low input (DT-LI), pasture and forest. The DT-LI treatment relies on manure application and legume cover crops to partly supply the N needed when corn is grown, and on cultivation to reduce the use of herbicides. Each watershed was instrumented with a flume and a Coshocton wheel sampler for runoff measurement. Carbon dioxide (CO2) evolved during incubation (115 days) of runoff samples was fitted to a first-order decomposition model to derive MinC. Annual soil (7.8 Mg/ha) and organic C (113.8 kg C/ha) losses were twice as much in the DT-LI than in the other watersheds (<3.6 Mg soil/ha), <60 kg C/ha). More than management practices, rainfall class (based on intensity and energy) was a better controller of sediment C concentration and biodegradability. Sediment collected during the low intensity (fall/winter) storms contained more organic C (37 g C/kg) and MinC (30-40% of sediment C) than materials displaced during the high intensity summer storms (22.1 g C/kg and 13%). These results suggest a more selective detachment and sorting of labile C fractions during low intensity storms. However, despite the control of low intensity storm on sediment C concentration and quality, increased soil loss with high energy rainfall suggests that a few infrequent but high energy storms could determine the overall impact of erosional events on terrestrial C cycling.