Academic journal article The American Midland Naturalist

Carbon and Nitrogen Sequestration in Two Prairie Topochronosequences on Contrasting Soils in Southern Wisconsin

Academic journal article The American Midland Naturalist

Carbon and Nitrogen Sequestration in Two Prairie Topochronosequences on Contrasting Soils in Southern Wisconsin

Article excerpt

ABSTRACT.-Prairie restoration has the potential to sequester nitrogen (N) and atmospheric carbon (C) in the soil, but the capability of a site to respond positively to prairie restoration depends on numerous factors such as soil parent material, topography and time. Soil bulk density in the top 10 cm and C and N concentrations at several intervals to a depth of 1 rn were measured in a tallgrass prairie topochronosequence at fine- and coarse-textured soil locations to evaluate the role of texture, slope and ecosystem age in controlling C and N sequestration following cessation of cultivation and subsequent prairie restoration. Soil C and N concentrations, contents and C:N ratios were significantly greater in fine-textured soils compared to sites with coarse-textured soil. Soil texture generally did not explain variations in the amounts or rates of C and N sequestration in the restored prairies. Soil surface bulk density was significantly correlated with slope, but not ecosystem age, at sites with coarse-- textured soil. Within the limits of this study, neither slope nor ecosystem age were correlated to bulk density at sites with fine-textured soil. Soil C content in the top 25 cm increased significantly as ecosystem age increased for the restored and remnant prairies at the fine-- textured location, but not at the coarse-textured location. Results demonstrate that a combination of soil parent material, topography and time since cessation of cultivation control the content and accumulation of C and N following prairie restoration. In the context of this study, the bottom line is that significant C sequestration was not achieved, given the current level and types of restoration management, within two and a half decades following conversion of cultivated cropland to prairie.

INTRODUCTION

In the mid-1800s, humans contributed to the most extensive ecological disturbance to the Upper Midwest since the end of the last ice age, ~11,000 y ago (Paul et al., 1997). Native tallgrass prairies were targeted for food production because the soils were fertile, rich in nutrients and organic matter (Miller, 1997), and could support and sustain human settlement. Consequently, these highly diverse ecosystems were converted to cropland causing rapid depletion of soil nutrients and, particularly, soil carbon (C), from oxidation and release to the atmosphere (Tiessen et al., 1982; Mann, 1986). For example, fewer than 800 ha of the estimated 850,000 ha of pre-settlement native prairie remain in Wisconsin, mostly as scattered remnants of 16 ha or less (Curtis, 1959).

Conversion of marginal or abandoned croplands to prairie vegetation provides erosion control and habitat for a diverse array of wildlife and is gaining popularity because of prairies' aesthetic value. Prairie vegetation is frequently restored with the goal of returning aboveground biodiversity to the ecosystem, but often without establishing the link to belowground biogeochemical processes that are characteristic of virgin prairies. Prairie restoration has been shown to lead to a gradual buildup of soil C and nitrogen (N) over time (Miller, 1997; Knops and Tilman, 2000). Therefore, conversion of agricultural or abandoned lands to restored prairie has the potential to sequester significant amounts of N and atmospheric C in soil (Fan et al., 1998).

In the 1980s the United States government implemented the Conservation Reserve Program (CRP) to reduce soil loss from highly erodible croplands. Though C sequestration was not an originally defined goal of the CRP, results have shown that cropland returned to natural vegetation can significantly increase C levels in the soil over time (Burke et al., 1989, 1995; Gebhart et al., 1994; Burke et al., 1995; Reeder et al, 1998; Robles and Burke, 1998; Potter et al, 1999). More recently, the United States Department of Agriculture's (USDA) Farm Service Agency (FSA) implemented a Conservation Reserve Enhancement Program (CREP) to provide economic incentives to landowners carrying out eligible environmental conservation practices (USDA-FSA, 2000). …

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