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Title: SEDIMENT CARBON CONCENTRATIONS AND TRANSPORT FROM SMALL WATERSHEDS UNDER VARIOUS CONSERVATION TILLAGE PRACTICES

Author
item Owens, Lloyd
item Malone, Robert - Rob
item Hothem, Daniel
item STARR, G - USDA-ARS 5342-45-00
item LAL, R - OSU,N COLUMBUS, OH

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2002
Publication Date: 5/10/2002
Citation: OWENS, L.B., MALONE, R.W., HOTHEM, D.L., STARR, G.C., LAL, R. SEDIMENT CARBON CONCENTRATIONS AND TRANSPORT FROM SMALL WATERSHEDS UNDER VARIOUS CONSERVATION TILLAGE PRACTICES. SOIL & TILLAGE RESEARCH. 2002. v.67. p.65-73.

Interpretive Summary: "Global warming" is a major environmental and political issue presently. Although there are controversies as to what extent or even whether global warming is occurring, it is generally accepted that atmospheric CO2 levels are increasing. Steps are being discussed on an international basis for the reduction of CO2 emissions (e.g. reduction of or cleaner burning of fossil fuels). In conjunction with this, practices to capture and store (or sequester) carbon (C) are being studied. One major potential area for C storage is agricultural crop production. Conventional tillage, i.e. moldboard plowing, exposes a lot of soil organic matter to the air with large potential C losses. Various conservation tillage practices store larger amounts of C in the soil than conventionally tilled soils. Using small watersheds near Coshocton, Ohio, different conservation tillage practices were compared with regard to the C content on sediments leaving the watersheds and the total amount of C moved on the sediments. The purpose was to determine whether C losses on sediments could be reduced by the selection of a conservation tillage practice. C contents on sediment were similar for no-till, chisel-plow, paraplow and disk practices, ranging from 2 to 3% C. Sediment losses differed, being greatest with disk. Therefore, the best way to reduce C losses on sediments from a field is to select a practice that reduces sediment losses. Such information will be useful not only to farmers and farm consultants but also to policy makers that make decisions concerning allowable procedures for C losses and storage.

Technical Abstract: Carbon sequestration by soils is viewed as a process that can reduce CO2 emissions and their potential impacts on global climate change. Therefore, impacts of various agricultural management practices on carbon (C) release/sequestration need to be assessed. The objectives of this study were to measure the carbon concentrations and transport in sediments lost with various tillage practices on small watersheds and to relate these losses to the management practices. Corn-soybean rotations with No-till, Chisel-plow and Paraplow were studied on small watersheds (0.55 - 0.79 ha). Disk tillage preceding the corn and soybean crops of a corn-soybean-wheat/clover rotation was also studied. A rye winter cover crop was used following soybean. Each small watershed is instrumented with a 60-cm H-flume mounted on a concrete approach and a Coshocton wheel for collecting a proportional sample of water and sediment. Samples of sediment in runoff were collected over a 15 year period and analyzed for total carbon (Tot C). Weighted averages of Tot C in the sediment that passed through the flumes during the treatment periods did not differ significantly among tillage treatments, although No-till was the highest (2.8%) and Paraplow was the lowest (2.1%). Average annual sediment loss was 532, 828 and 956 kg ha-1 for No-till, Chisel-plow and Disk, respectively. Annual average transport of Tot C (the product of total sediment transported and the Tot C concentration) in the sediment was 13.7, 15.0, 12.7 and 22.2 kg ha-1 for No-till, Chisel-plow, Paraplow and Disk, respectively. Although tillage practices may reduce C transport in sediment by lowering concentrations, a greater factor for reducing C movement is reducing sediment movement.