Introduction

Management practices can have major impacts on soil organic carbon (SOC) levels, gains, and losses. There is wide acceptance that cultivating native land causes loss of soil organic matter. Davidson and Ackerman (1993) reported 20% to 40% loss of soil organic matter following the conversion of previously untilled soils to agricultural production. Changes in agricultural production are reversing this trend (Buyanovsky and Wagner, 1998). Conversion of land from plow tillage to long-term no-tillage management often increases soil organic C and N content (Doran, 1980, 1987; McCarty et al., 1995; McCarty and Meisinger, 1997).

The impacts of tillage and cropping rotations on SOC have been studied at several sites over various time periods. Increased SOC was measured in long-term (8 to 24 years) studies with no-tillage practices in the southeastern Coastal Plain of the United States (Hunt et al., 1996), Kentucky (Ismail et al., 1994), Illinois (Hussain et al., 1999), Iowa (Karlen et al., 1994), Nebraska (McCallister and Chen, 2000), North Dakota (Halvorson et al., 2002), Alberta, Canada (Nyborg et al., 1995), Saskatchewan, Canada (Campbell and Zentner, 1993; Campbell et al., 1995, 1996), and Argentina (Alvarez et al., 1995).

The SOC is lost from soil through several pathways, including mineralization following tillage, translocation with sediment, and leaching from the soil profile. Because tillage aerates soil and allows greater C mineralization (Eghball et al., 1994), a reduction in tillage intensity decreases SOC loss. Reicosky et al. (1995) identified large gaseous losses of soil C following moldboard plowing compared with relatively small losses with no till.

Among the multiple pathways of C loss from agricultural fields is C lost with sediment. Many studies of C loss from cropped fields were runoff plot (Massey and Jackson, 1952; Wan and El-Swaify, 1997; Zobisch et al., 1995) or erosion plot studies (Ambassa-Kiki and Nill, 1999; Kaihura et al., 1999) that had C as part of a group of nutrients instead of the central focus. Sediments enriched with organic C compared with surface soil have been observed in soils ranging from Wisconsin silt loams (Massey and Jackson, 1952) to clay soils in Hawaii (Wan and El-Swaify, 1997). In reviewing literature about C redistribution and loss by erosion, Gregorich et al. (1998) concluded that erosion usually resulted in decreased primary production and that SOC decreased because of a reduction in primary production.

Although numerous studies of SOC loss have been conducted, the concentrations and losses of total organic carbon (TOC) moving through soil profiles have received little attention. There are studies of dissolved organic carbon (DOC) in streams draining forested areas in New England. Values for DOC ranged between 0.3 and 2.0 mg/L in the stream tributaries of Hubbard Brook Experimental Forest in New Hampshire (Likens et al., 1977). In two paired streams draining forested watersheds in Maine, DOC concentrations of 2.0 and 2.2 mg/L were found (David et al., 1992). Owens et al. (1991) compared TOC concentrations in stormflow and baseflow from wooded, nonwooded, and mixed-management watersheds in Ohio. During the 10 years of study, average TOC concentrations in stormflow ranged from 12.8 (wooded watershed) to 29.7 mg/L (unimproved pasture watershed). Baseflow concentrations ranged from 5.5 (unimproved pasture watershed) to 8.5 mg/L (watershed with more than 50% pasture and meadow). Concentrations of TOC in developed springs under rotational pastures in east-central Ohio ranged from 2 to 8 mg/L (Owens et al., 1998). Jardine et al. (1990) investigated DOC transport through a forested Tennessee hillslope on the basis of single rainfall events. In shallow subsurface flow (up to 1-m depth), DOC ranged up to nearly 11 mg/L, and the DOC concentrations reported for lower subsurface flow were less than 2 mg/L.

This chapter provides an overview of the research conducted at the North Appalachian Experimental Watershed that focuses on C that is moved from agricultural fields with sediment, and C that moves in water through the soil profile.

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