Bio-based energy is key to developing a globally sustainable low-carbon economy. Lignocellulosic feedstock production on marginally productive croplands is expected to provide substantial climate mitigation benefits, but long-term field research comparing greenhouse gas (GHG) outcomes during the production of annual versus perennial crop-based feedstocks is lacking. Here, we show that long-term (16 years) switchgrass (Panicum virgatum L.) systems mitigate GHG emissions during the feedstock production phase compared to GHG-neutral continuous corn (Zea mays L.) under conservation management on marginally productive cropland. Increased soil organic carbon was the major GHG sink in all feedstock systems, but net agronomic GHG outcomes hinged on soil nitrous oxide emissions controlled by nitrogen (N) fertilizer rate. This long-term field study is the first to demonstrate that annual crop and perennial grass systems respectively maintain or mitigate atmospheric GHG contributions during the agronomic phase of bioenergy production, providing flexibility for land-use decisions on marginally productive croplands.

There is a very large global pool of soil inorganic carbon (SIC), but its formation, quantity, and dynamics are uncertain. The major problems in determining SIC stocks are the incomplete global database and the difficulty in separating pedogenic from lithogenic carbonate sources.

Soil organic C (SOC) is essential to agricultural productivity and sustainability in response to climate and land-use change. Here, we examine 14 sites across the U.S. Great Plains to determine the sensitivity of important SOC fractions to climatic gradients (temperature and precipitation) and land-use change (native, conservation reserve program [CRP], and cropped). We measured particulate organic matter C (POM-C), soil mineral associated C (Cmin-C), soil microbial biomass C (SMB-C), and soil aggregate stability (%AggStab). All fractions (POM-C, SMB-C, and %AggStab) except Cmin-C were affected by land-use and decreased from native > CRP > cropped sites. Total SOC and all the fractions decreased with increasing temperature and increased with greater clay content. Surprisingly, only the Cmin-C as well as the %AggStab increased with increasing mean annual precipitation (MAP)/evapotranspiration (ET) ratio; the more labile fractions POM-C and SMB-C did not. Despite greater %AggStab, there was not POM-C protection, suggesting that aggregate turnover and subsequent C loss was greater in sites with more moisture. The Cmin-C fraction comprised the majority of total SOC (70%) and also comprised most of the whole soil response to temperature and moisture gradients. The POM-C fraction could be used as an easily measured indicator of land-use impacts in soil, since POM-C and SMB-C were highly correlated. Conservation practices that promote soil aggregation and reduce disturbance and erosion will be critical in maintaining mineral soil C and ameliorating soil C loss though increased temperatures. These practices have additional benefit of building the POM-C fraction and SMB-C.

In the Arctic tundra and boreal regions, permafrost-affected soils (Gelisols) have segregated ice that accumulates and thaws during freeze–thaw cycles resulting in cryoturbated soils. These cryoturbated soils (Turbels) have warped, broken, or involuted horizons and cryostructures that require sampling protocols different than soils not affected by permafrost. We provide a general overview of the cryoturbated soil profiles associated with different cryogenic landscapes and landforms and a specific protocol for description and sampling pedons with permafrost.

Net benefits of bioenergy crops, including maize and perennial grasses such as switchgrass, are a function of several factors including the soil organic carbon (SOC) sequestered by these crops. Life cycle assessments (LCA) for bioenergy crops have been conducted using models in which SOC information is usually from the top 30 to 40 cm. Information on the effects of crop management practices on SOC has been limited so LCA models have largely not included any management practice effects. In the first 9 years of a long-term C sequestration study in eastern Nebraska, USA, switchgrass and maize with best management practices had average annual increases in SOC per hectare that exceed 2 Mg C year−1 (7.3 Mg CO2 year−1) for the 0 to 150 soil depth. For both switchgrass and maize, over 50 % of the increase in SOC was below the 30 cm depth. SOC sequestration by switchgrass was twofold to fourfold greater than that used in models to date which also assumed no SOC sequestration by maize. The results indicate that N fertilizer rates and harvest management regimes can affect the magnitude of SOC sequestration. The use of uniform soil C effects for bioenergy crops from sampling depths of 30 to 40 cm across agro-ecoregions for large scale LCA is questionable.

Turfgrass is a major vegetation type in the urban and suburban environment. Management practices such as species selection, irrigation, and mowing may affect C input and storage in these systems. Research was conducted to determine the rate of soil organic C (SOC) changes, soil C sequestration, and SOC decomposition of fine fescue (Festuca spp.) (rainfed and irrigated), Kentucky bluegrass (Poa pratensis L.) (irrigated), and creeping bentgrass (Agrostis palustris Huds.) (irrigated) using C isotope techniques. We found that 4 yr after establishment, about 17 to 24% of SOC at 0 to 10 cm and 1 to 13% from 10 to 20 cm was derived from turfgrass. Irrigated fine fescue added the most SOC (3.35 Mg C ha−1 yr−1) to the 0‐ to 20‐cm soil profile but also had the highest rate of SOC decomposition (2.61 Mg C ha−1 yr−1). The corresponding additions and decomposition rates for unirrigated fine fescue, Kentucky bluegrass, and creeping bentgrass in the top 20‐cm soil profile were 1.39 and 0.87, 2.05 and 1.73, and 2.28 and 1.50 Mg C ha−1 yr−1, respectively. Irrigation increased both SOC input and decomposition. We found that all turfgrasses exhibited significant C sequestration (0.32–0.78 Mg ha−1 yr−1) during the first 4 yr after turf establishment. The net C sequestration rate was higher, however, for irrigated fine fescue and creeping bentgrass than for Kentucky bluegrass. To evaluate total C balance, additional work is needed to evaluate the total C budget and fluxes of the other greenhouse gases in turfgrass systems.

Grasslands in the Conservation Reserve Program (CRP) in the USA may be converted to grain crops for bioenergy. The effect of no‐till conversion of a smooth bromegrass ( Bromus inermis Leyss) grassland to no‐till corn ( Zea mays L.) production on soil organic carbon (SOC) in the western Corn Belt was monitored for over 6 yr. A different 13 C/ 12 C isotope signature is imparted to SOC by C4 plants including corn versus C3 plants such as bromegrass. Changes in C isotope ratios in SOC in three soil depths (0‐ to 5‐, 5–10, and 10–30 cm) by particle size was also monitored during ∼6.5 yr of no‐till corn production at two different N levels (60 and 120 kg ha −1 ). Soil was collected eight times during the study from the 0‐ to 5‐ and 5‐ to 10‐cm depths, and at four of these times from the 10‐ to 30‐cm depth from each of the N rate replicates. Because fertilizer N had no significant effect over years on any of the aboveground biomass production variables, the data from both N treatments was combined for regression analysis to determine the effects of years of no‐till corn production on SOC variables. Total SOC did not change significantly at any depth during the study, but there was a significant change in the source of the SOC. Total C4‐C increased over this time, while C3‐C decreased in the 0‐ to 5‐ and 5‐ to 10‐cm depth, while neither changed in the 10‐ to 30‐cm depth. In the 0‐ to 5‐ and 5‐ to 10‐cm depths, largest loss of C3‐C was from 2‐mm aggregates, while largest increases in C4‐C were in the 1‐, 0.5‐, 0.25‐, and 0.125‐mm aggregates. If CRP grasslands are converted to grain crop production, the data from this study strongly support the use of no‐till farming practices as a method of conserving the SOC that was sequestered during the time period that the land was in the CRP.

abstract

Sinking agricultural botanical and soil residues to the deep seafloor may not be a viable option for long-term carbon sequestration.

Relatively little is known about soil climate in Antarctica. The purpose of our research was to describe a cooperative soil climate monitoring project in the McMurdo Dry Valleys and other ice-free areas of the Ross Island Region of Antarctica. There are seven soil climate stations that monitor air temperature, relative humidity, wind speed and direction, solar radiation, and soil moisture and temperature in which hourly measurements are recorded. The initial project objective, in 1999, was to determine the impact of fuel spills on the biological, chemical, and physical properties of Antarctic soils, which was lead by Landcare Research of New Zealand. When the initial project ended in 2002, the control sites were continued as long-term monitoring stations. At each site, soils were described and sampled for characterization analyses. The soils are coarse textured with significant amounts and sizes of coarse fragments throughout the profile with little soil development (or horizonation). Mean annual air temperatures (MAAT) range from −17 to −24°C. The mean annual soil temperatures (MAST) range from −14.6 to −23.5°C. The average maximum thaw depth ranged from 5.5 cm to more than 85 cm. Average active layer water contents are low and tend to increase with depth. The data, soil descriptions, soil characterization data, and station records from this project are available through the National Soil Survey Center's web page (http://soils.usda.gov/survey/scan/; verified 22 June 2009). As long as the project continues, annual maintenance and data retrieval are necessary. The importance of this project is that it provides NRCS an opportunity to gather data in an area sensitive to global climate change.

The Arctic soil organic-carbon pool is a significant, but poorly constrained, carbon store. The most cited pool size estimates are based on a study that severely undersamples Arctic soils, with only five out of the 48 soils examined actually from the Arctic region. Furthermore, previous measurements have been confined to the top 40 cm of soil. Here, we present 1-m-deep measurements of soil organic carbon obtained at 117 locations in the North American Arctic region. To this dataset we add previously published measurements to generate a total sample size of 139 North American Arctic soils. We show that soil organic-carbon stores are highly dependent on landscape type, being highest in lowland and hilly upland soils, where values average 55.1 and 40.6 kg soil organic carbon m −2 respectively, and lowest in rubbleland and mountain soils, where values average 3.4 and 3.8 kg soil organic carbon m −2 respectively. Extrapolating our measurements using known distributions of landscape types we estimate that the total organic carbon pool in North American Arctic soils, together with the average amount of carbon per unit area, is considerably higher than previously thought. Our estimates of the depth distribution and total amount of organic carbon in North American Arctic soils will form an important basis for studies examining the impact of climate warming on CO 2 release in the region.

Three-dimensional ground-penetrating radar (3D GPR) was used to investigate the subsurface structure of ice-wedge polygons and other features of the frozen active layer and near-surface permafrost near Barrow, Alaska. Surveys were conducted at three sites located on landscapes of different geomorphic age. At each site, sediment cores were collected and characterised to aid interpretation of GPR data. At two sites, 3D GPR was able to delineate subsurface ice-wedge networks with high fidelity. Three-dimensional GPR data also revealed a fundamental difference in ice-wedge morphology between these two sites that is consistent with differences in landscape age. At a third site, the combination of two-dimensional and 3D GPR revealed the location of an active frost boil with ataxitic cryostructure. When supplemented by analysis of soil cores, 3D GPR offers considerable potential for imaging, interpreting and 3D mapping of near-surface soil and ice structures in permafrost environments. Copyright (C) 2007 John Wiley & Sons, Ltd.

The objective of this study was to compare mid-infrared (MIR) an near-infrared (NIR) spectroscopy (MIRS and NIRS, respectively) not only to measure soil carbon content, but also to measure key soil organic C (SOC) fractions and the delta C-13 in a highly diverse set of soils while also assessing the feasibility of establishing regional diffuse reflectance calibrations for these fractions. Two hundred and thirty-seven soil samples were collected from 14 sites in 10 western states (CO, IA, MN, MO, MT, ND, NE, NM, OK, TX). Two subsets of these were examined for a variety of C measures by conventional assays and NIRS and MIRS. Biomass C and N, soil inorganic C ( SIC), SOC, total C, identifiable plant material (IPM)

The physical and chemical properties of Arctic tundra soils were studied along a 250-km latitudinal transect in northern Alaska. The transect includes the nonacidic tundra of the Arctic Coastal Plain, the moist nonacidic tundra of the northern Arctic Foothills, and moist acidic tundra of the southern Arctic Foothills. The parent material of the coastal plain consists of carbonate-rich alluvium. The northern foothills have a mantle of calcareous loess. Further south the parent materials are moraines of late Quaternary. Vegetation changes from sedges on the coastal plain, to grasses on the northern foothills, and tussock and shrub tundra in southern foothills. Following the same order, soil pH and base saturation decrease and soil acidity increases. Most of the soil exchangeable acidity and cation exchange capacity are from soil organic matter.

The objective of this study was to evaluate potential use of the naturally occurring isotopic carbon (C) in soil organic matter to help evaluate paleoclimate in the Central United States. Sampling sites were selected on major geomorphic units with similar slope and aspect in three soil temperature regimes and three soil moisture regimes within the historic grasslands in US Great Plains and Western Corn Belt. Soil samples were collected from approximate 0- to 5- and 5- to 10-cm (A1 and A2 profile) depths and by genetic soil horizon thereafter in pits dug by backhoe or by hand to ~2 m depth. Bulk density and soil texture were determined. Sieved, handpicked, and delimed subsamples of soil from each horizon were analyzed for total soil organic carbon (SOC) and δ13C and 14C dated (as mean residence time of SOC in calendar yr B.P.). Data from some sites support that major aeolian movement of soil occurred during the Holocene, often coincidental with literature reports of long periods of drought. However, soil profiles provide a low-resolution record of drought and/or wetter climatic conditions and thus time frames are general. Measurement of SOC age and δ13C signature in soil horizons was related to preboreal warming during entry into the Holocene. An important question raised by our data but requiring further confirmation by other studies is the timing of the peak of the Medieval Warm Period that is reported to have occurred prior to commencement of climate cooling that preceded the Little Ice Age. Based on δ13C, our data indicate a change from C4 plants to increasing C3 plant dominance (as a surrogate of cooler temperature) at ~1,500 yr B.P., whereas the reported start of the Little Ice Age is ~600 yr B.P. In summary, the approach we used holds promise as an additional proxy for evaluating prior climate back thousands of years, but additional measurements besides those from the isotopes of C will be needed.

About the Editors Acknowledgements Preface Foreward, D. Reed, White House Global Change Office Historical Perspectives Introduction, J.M. Kimble, R. Lal, and R. Follett National Trends in Adopting Conservation Practices as Best Management Practices, H. Bloodworth Why Carbon Sequestration in Soil? R. Lal Historical Perspective in Land Use Change and Soil Carbon Dynamics, F. Miller Conservation Tillage and Residue Management Effects of Crop Rotations on Soil Organic Carbon in Semiarid Prairie - 10 Year Study, C.A. Campbell, R.P. Zentner, V.O. Biederbeck, and B.G. McConkey Mulch Rate and Tillage Effects on Carbon Sequestration and CO2 Flux from an Alfisol of Central Ohio, S.W. Duiker and R. Lal Effects of Tillage on Inorganic C Distribution in Soils of the Northern Great Plains of the U.S., L.J. Cihacek and M.G. Ulmer Climatic Influences on C Storage with no Tillage, A. Franzluebbers and J. Steiner Long-Term Effects of Moldboard Plowing on Tillage-Induced CO2 loss, D. Reicosky Tillage-Soil Organic Matter Relationship in Long-Term Experiments, E. Micheli Effect of Conservation Tillage on C Sequestration of C Duplex Soil of SE Australia, W. Slattery and A. Surapaneni Monitoring and Assessment Analysis and Reporting of C Sequestration and Greenhouse Gases for Conservation Districts in Iowa, J. Brenner Estimating Regional C Sequestration Potential of Agricultural Management Options Using GIS and Dynamic SOM Model, P. Falloon Management Induced Changes Affecting Soil C Storage and Nutrient Cycling in Conventional and Organic/Low-Input Systems, W.R. Horwath Land Use Effects on Soil Carbon Pool in Two Major Land Resources Areas of Ohio, A. Lantz, R. Lal, and J. Kimble CQESTER - Predicting Carbon Sequestration in Agricultural Soils, R.W. Rickman, C.L. Douglas, and S.L. Albrecht Case Study of Cost vs. Accuracy of Measuring Carbon Stock in Terrestrial Ecosystems, G. Smith Soil Management Soil Fertility Management with Zeolite Amendments. I. Zeolite Effect on the Carbon Sequestration. A Review, E. Filcheva and K. Chaklov Effect of Rotation on the Composition of Soil Organic Matter, E. Filcheva and T. Mitova Effect of Climate Change on Management Soil C: Northern Peat Soils, T. Moore Application of Management Decision Aid for Sequestration of C and N in Soil, A. Olness Soil C Turnover after 28 Years of Residue Managed Wheat and Sorghum Production, C. Rice Soil Structure and C Sequestration Soil Organic Carbon Pool in Forest and Pasture of a Reclaimed Mine-Land in Ohio, V. Akala and R. Lal Efficiencies of Conversion of Residue C to Soil C, C.A. Campbell, B.G. McConkey, S. Gameda, C. Izaurralde, B.C. Liang, R.P. Zentner, and D. Sabourin Changes of Organic Matter and Aggregate Stability of the Arable Waterlogged Soils, R. Dilkova, E. Filcheva, G. Kerchev, and M. Kercheva Economics of C Sequestration Designing Efficient Practices for Agricultural Soil Carbon Sequestration, J. Antle and S. Mooney Making Soil C Sequestration an Economic Undertaking for Farmers, T. Fancl Economic Impacts of C Sequestration Policy Scenarios in the U.S. House Operationalizing C Sequestration in Soils Through Appropriate Policies, D. Zilberman Policy Issues and Industrial View Points Carbon Sequestration Potential Canadian Farmland: A Farmer's Perspective, J. Bennett Role of Commercial Energy Companies in C Sequestration in Soils, A. Donelly Contribution of Root-Derived Carbon Soil Organic Matter, W.J. Gale, C.A. Cambardella Carbon Sequestration in Soil with Conservation Tillage, J. Kinsella Policy Issues of C Sequestration in Soils, A. Manale Farming Carbon Through Conservation Tillage and Residue Management, B. Richards Making the Market for Soil Carbon a Reality, M. Walsh Role of Agro-Industries in Realizing Potential of Soil C Sinks, B. Alesii Regional Pools Potential for Carbon Accumulation and Sequestration under Brachiaria Pastures in Brazil, R. Boddey Carbon Content of Desert and Semi-Desert Soils for Central Asia, E. Lioubimsteva and J. Adams Pastureland Use in Southeastern US: Implications for C Sequestration, R. Conant, et al On-Farm C Sinks: Production and Sequestration Complementarities, J. Hopkins, et al C Balance of Hungarian Soils, T. Nemeth, et al Some Key Uncertainties in the Global Distribution of Soil and Peat Carbon, E. Lioubimsteva and J.M. Adams Summary Where Do We Go Now in the Interaction of Policy and Science? J. Kimble and L. Everett

This chapter aims to identify research and development priorities with regard to soil carbon (C) dynamics in forest soils. Afforestation on agricultural soils can enhance the C pool in soil. The rate of soil C sequestration, however, is site-specific and needs to be determined in relation to soil type, the quantity and quality of the biomass returned to the soil, and the humification efficiency depending on climate, moisture, and temperature regimes. The baseline information on soil C pool and fluxes is important for developing a strategy for international negotiation and for sustainable management of forest resources. The potential of C sequestration in forest soils needs to be addressed both for soil organic carbon and for soil inorganic carbon. Assessing the magnitude, fluxes, and components of the soil C pool is a pioneering field of research. Impact of management practices on pool and fluxes of C in forest soils are not known and need to be determined.

Hydrocarbon spills have occurred on Antarctic soils where fuel oils are utilized, moved or stored. We investigated the effects of hydrocarbon spills on soil temperature and moisture regimes by comparing the properties of existing oil contaminated sites with those of nearby, uncontaminated, control sites at Scott Base, the old Marble Point camp, and Bull Pass in the Wright Valley. Hydrocarbon levels were elevated in fuel-contaminated samples. Climate stations were installed at all three locations in both contaminated and control sites. In summer at Scott Base and Marble Point the mean weekly maximum near surface (2 cm and 5 cm depth) soil temperatures were warmer (P<0.05), sometimes by more than 10°C, at the contaminated site than the control sites. At Bull Pass there were no statistically significant differences in near-surface soil temperatures between contaminated and control soils. At the Scott Base and Marble Point sites soil albedo was lower, and hydrophobicity was higher, in the contaminated soils than the controls. The higher temperatures at the Scott Base and Marble Point hydrocarbon contaminated sites are attributed to the decreased surface albedo due to soil surface darkening by hydrocarbons. There were no noteworthy differences in moisture retention between contaminated and control sites.

Terrestrial ecosystems are a major sink for carbon. Carbon dioxide is removed from the atmosphere by the photosynthetic process and stored in the plant biomass. Forest stands are manipulated in many ways such as thinning, clear-cutting, introduction of exotic tree species, forest fertilization, forest fire prevention, inputs of nutrients from rainfall deposition, acid rain, and introduction of nonnative insects. In contrast to clearing for agriculture, which takes land out of forest cover for a period of time, forest management practices can include clear-cutting or partial cutting followed by reforestation. As forest systems are so diverse, there are no standard sets of assumptions that can describe the effects of possible climate change. About 120 Mha of forestlands have been converted to other uses, and much of that land is now productive agriculture land. The chapter also presents an overview of the key concepts discussed in this book.

Soil organic carbon (SOC) was measured in 17 pedons, representing major agricultural soils in Albania, The soils studied were Inceptisols, Vertisols, Mollisols, and Alfisols. Within each order, the wet members (aquic suborders) had 10 times or more SOC than their well-drained counterparts. Radiocarbon dates were determined on wood fragments found in a few of the soils. The steady-state rates of accumulation range from 20 to 60 g m(-1) m(-2) yr(-1) in the wet soils. Only one well-drained soil was available for comparison and this had an accumulation rate of SOC of <1 g m(-1) m(-2) yr(-1). Drainage of the wet soils results in a marked decrease in SOC. The rate of decrease is much smaller (26 g m(-1) m(-2) yr(-1) during a 38-yr period) than the accumulation rate,,which was about 210 g m(-1) m(-2) yr(-1) (during 2000 yr) in the one pedon studied. In the same climatic environment, the well-drained soils accumulate SOC at significantly lower rates than their poorly drained counterparts, making the Former inefficient sinks of SOC. Thus, from the point of view of sinks of atmospheric CO2, emphasis must be given to the wetland soils.