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Title: CARBON CONCENTRATIONS AND TRANSPORT IN SEDIMENT LEAVING SMALL, CROPPED WATERSHEDS

Author
item Owens, Lloyd
item Malone, Robert - Rob
item STARR, G - THE OHIO STATE UNIVERSITY
item LAL, R - THE OHIO STATE UNIVERSITY

Submitted to: International Soil Conservation Organization (ISCO)
Publication Type: Proceedings
Publication Acceptance Date: 4/19/2001
Publication Date: N/A
Citation: N/A

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 carbon dioxide levels are increasing. Steps are being discussed on an international basis for the reduction of carbon dioxide 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 Ccontent on sediments leaving the watersheds and the total amount of C move 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: With the current interest in CO2 emissions and their potential impacts on global climate change, it is important to evaluate the role of agriculture in the global carbon (C) budget. Impacts of various tillage practices on C release/sequestration need to be assessed. At a USDA-ARS research station near Coshocton, Ohio, various conservation tillage practices including corn/soybean rotations with No-till (NT), Chisel-plow (CP), Paraplow (PP), and Disk (D) preceding the corn and soybean crops of a corn/soybean/ wheat-meadow rotation were studied on small watersheds (0.55 to 0.79 ha). Each watershed was 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. Over a 13 year period, samples of sediment deposited in the flume approach and in runoff were collected. These samples were analyzed for total C, and comparisons of soil C were made among management practices. Weighted averages of soil C in the sediment passing through th flumes did not differ significantly among tillage treatments, although NT was the highest (2.8%) and CP was the lowest (1.9%). Weighted averages of soil C in the flume floor sediments were slightly lower with NT being the highest (2.3%) and PP being the lowest (2.1%). For comparison, weighted soil C averages in sediment from small fertilized, pastured watersheds ranged from 5.2 to 7.2%. Average annual sediment loss was 437, 656, and 753 kg/ha for NT, CP, and D, respectively. Annual average transport of soil C (total sediment transported x C content) in the sediment was 11.8, 12.0, 10.9, and 17.6 kg/ha for NT, CP, PP, and D, respectively. Although tillage practices may reduce C transport in sediment by lowering C content, a greater factor for reducing C movement is reducing sediment movement.