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Showing papers on "Soil organic matter published in 1996"



Journal ArticleDOI
TL;DR: In this article, a discrepancy of approximately 350 × 1015 g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo-referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project.
Abstract: Summary The soil is important in sequestering atmospheric CO2 and in emitting trace gases (e.g. CO2, CH4 and N2O) that are radiatively active and enhance the ‘greenhouse’ effect. Land use changes and predicted global warming, through their effects on net primary productivity, the plant community and soil conditions, may have important effects on the size of the organic matter pool in the soil and directly affect the atmospheric concentration of these trace gases. A discrepancy of approximately 350 × 1015 g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo-referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project. This database holds 4353 soil profiles distributed globally which are considered to represent the soil units shown on a 1/2° latitude by 1/2° longitude version of the corrected and digitized 1:5 M FAO–UNESCO Soil Map of the World. Total soil carbon pools for the entire land area of the world, excluding carbon held in the litter layer and charcoal, amounts to 2157–2293 Pg of C in the upper 100 cm. Soil organic carbon is estimated to be 684–724 Pg of C in the upper 30 cm, 1462–1548 Pg of C in the upper 100 cm, and 2376–2456 Pg of C in the upper 200 cm. Although deforestation, changes in land use and predicted climate change can alter the amount of organic carbon held in the superficial soil layers rapidly, this is less so for the soil carbonate carbon. An estimated 695–748 Pg of carbonate-C is held in the upper 100 cm of the world's soils. Mean C: N ratios of soil organic matter range from 9.9 for arid Yermosols to 25.8 for Histosols. Global amounts of soil nitrogen are estimated to be 133–140 Pg of N for the upper 100 cm. Possible changes in soil organic carbon and nitrogen dynamics caused by increased concentrations of atmospheric CO2 and the predicted associated rise in temperature are discussed.

3,163 citations


Book
21 Jan 1996
TL;DR: In this article, the authors present an overview of the role of soil in the formation and evolution of Soil Microbiology and Biochemistry in Perspective, as well as its relationship with Soil Organisms.
Abstract: Soil Microbiology and Biochemistry in Perspective. Soil as a Habitat for Organisms and Their Reactions. Methods for Studying Soil Organisms. Components of the Soil Biota. Occurrence and Distribution of Soil Organisms. Carbon Cycling and Soil Organic Matter. Dynamics of Residue Decomposition and Soil Organic Matter Turnover. Ammonification and Nitrification. The Fate of Nitrates. Closing the Nitrogen Cycle: Return of Nitrogen to the Soil. Mycorrhizal Relationships. The Commercialization of Organisms. Phosphorus Transformations. Sulfur Transformations in Soil. Microbial Transformations of Metal. Chapter References and Suggested Reading. Subject Index.

2,974 citations


Journal ArticleDOI
Ralf Conrad1
TL;DR: It is completely unclear how important microbial diversity is for the control of trace gas flux at the ecosystem level, and different microbial communities may be part of the reason for differences in trace gas metabolism, e.g., effects of nitrogen fertilizers on CH4 uptake by soil; decrease of CH4 production with decreasing temperature.

1,622 citations


Journal ArticleDOI
01 Nov 1996-Geoderma
TL;DR: In this article, a conceptual model of the processes by which plant leaf and root litter is transformed to soil organic C and CO 2 is presented, which is viewed as resulting from three general sets of characteristics.

1,409 citations


Book ChapterDOI
01 Jan 1996

1,197 citations


Book
01 Nov 1996
TL;DR: Pathways and processes in decomposition foraging, feeding and feedback manipulation of plant litter quality synchrony and soil organic matter - theory into practice?
Abstract: Pathways and processes in decomposition foraging, feeding and feedback manipulation of plant litter quality synchrony and soil organic matter - theory into practice? building soil organic matter modelling - providing the framework.

933 citations


Book
01 Jan 1996
TL;DR: In this paper, Canadian and FAO Soil Classification Systems were used to classify the Soils around us and their properties, including: 1. Formation of Soils from Parent Materials. 2. Soils and Chemical Pollution. 3. Soil Architecture and Physical Properties.
Abstract: 1. The Soils Around Us. 2. Formation of Soils from Parent Materials. 3. Soil Classification. 4. Soil Architecture and Physical Properties. 5. Soil Water: Characteristics and Behavior. 6. Soil and the Hydrologic Cycle. 7. Soil Aeration and Temperature. 8. Soil Colloids: Seat of Soil Chemical and Physical Activity. 9. Soil Acidity. 10. Soils of Dry Regions: Alkalinity, Salinity, and Sodicity. 11. Organisms and Ecology of the Soil. 12. Soil Organic Matter. 13. Nitrogen and Sulfur Economy of Soils. 14. Soil Phosphorus and Potassium. 15. Micronutrient and Other Trace Elements. 16. Practical Nutrient Management. 17. Soil Erosion and Its Control. 18. Soils and Chemical Pollution. 19. Geographic Soils Information. 20. Global Soil Quality as Affected by Human Activities. Appendix A: Canadian and FAO Soil Classification Systems. Appendix B: SI Unit Conversion Factors and Periodic Table of the Elements. Glossary. Index.

877 citations


BookDOI
01 Jan 1996
TL;DR: Methods in soil biology , Methods in soil Biology , مرکز فناوری اطلاعات £1,000,000 to £1,500,000 (US$2,400,000) is suggested for the total cost of the project to be in the range of $10m to $25m.
Abstract: Methods in soil biology , Methods in soil biology , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

817 citations


01 Jan 1996
TL;DR: The Chemical Structure of Humic Substances: Recent Advances (Cesareo Saiz-Jimenez). Chapter 2. Humus in World Soils (Francis Andreux). Chaptr 3. Organic Matter Dynamics in Forest Soils of Temperate and Tropical Ecosystems (Wolfgang Zech et al.).
Abstract: Preface. Contributors.Chapter 1. The Chemical Structure of Humic Substances: Recent Advances (Cesareo Saiz-Jimenez). Chapter 2. Humus in World Soils (Francis Andreux). Chaptr 3. Organic Matter Dynamics in Forest Soils of Temperate and Tropical Ecosystems (Wolfgang Zech et al.). Chapter 4. Dissolved Humus in Soil Waters (Adam Zsolnay). Chapter 5. Humus and Soil Conservation (Alessandro Piccolo). Chapter 6. Microorganisms and Humus in Soils (Heribert Insam). Chapter 7. Humus and Enzyme Activity (Paolo Nanniperi, P. Sequi, P. Fusi). Chapter 8. Organisms and Humus in Soils (Lijbert Brussaard, N.J. Juma). Chapter 9. Biological Activity of Humus (Serenella Nardi, G. Concheri, G. Dell'Agnola). Chapter 10. Organic Forms of N in Soil (Kenneth R. Kelley, F.J. Stevenson). Chapter 11. Dynamics of Organic Phosphorus in Soils under Natural and Agricultural Ecosystems (Jacob Magid, H. Tiessen. L.M. Condron). Chapter 12. Soil Organic Sulphur and its Turnover (Fang-Jie Zhao, J. Wu, S.P. McGrath). Chapter 13. Organic Matter Reactions Involving Micronutrients in Soils and their Effect on Plants (Yona Chen). Chapter 14. Humic-like Substances in Organic Amendments and Effects on Native Humic Substances (Nicola Senesi, T.M. Miano, G. Brunetti). Chapter 15. Interactions of Humic Substances and Soil Clays (Juan Cornejo, M.C. Hermosin). Chapter 16. Soil Organic Matter as a Factor Influencing the Fate of Organic Chemicals in the Soil Environment (Josef Kozak). Subject Index.

635 citations



Journal ArticleDOI
TL;DR: In this article, the nature of organic carbon in the < 2, 2-20, 20-53, 53-200, and 200-2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS).
Abstract: The nature of organic carbon in the < 2, 2–20, 20–53, 53–200, and 200–2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS). Analyses were repeated after high energy ultraviolet photo-oxidation was performed on the three finest fractions. All four soils, studied contained appreciable amounts of physically protected carbon while three of the soils contained even higher amounts of charcoal. It was not possible to measure the charcoal content of soils directly, however, after photo-oxidation, charcoal remained and was identified by its wood-like morphology revealed by scanning electron microscopy (SEM) together with a highly aromatic chemistry determined by solid state 13C n.m.r. Charcoal appears to be the major contributor to the 130 ppm band seen in the n.m.r. spectra of many Australian soils. By using the aromatic region in the n.m.r. spectra, an approximate assessment of the charcoal distribution through the size fractions demonstrated that more than 88% of the charcoal present in two of the soils occurred in the < 53 µm fractions. These soils contained up to 0.8 g C as charcoal per 100 g of soil and up to 30% of the soil carbon as charcoal. Humic acid extractions performed on soil fractions before and after photo-oxidation suggest that charcoal or charcoal-derived material may also contribute significantly to the aromatic signals found in the n.m.r. spectra of humic acids. Finely divided charcoal appears to be a major constituent of many Australian soils and probably contributes significantly to the inert or passive organic carbon pool recognised in carbon turnover models.

Journal ArticleDOI
TL;DR: In this article, competitive sorption was tested between atrazine (AT) and other co-solutes in water suspensions of natural and model sorbents, including a mineral soil, a peat soil, soil humic acid particles, a glassy polymer, and a mesoporous silica gel.
Abstract: This is part of a larger study that addresses the question of whether site-specific sorption of organic compounds takes place in soil organic matter (SOM). Competitive sorption is one indication that such interactions may take place. Competitive sorption was tested between atrazine (AT) and other co-solutes in water suspensions of natural and model sorbents. The co-solutes included several s-triazine analogs, a substituted benzene analog (5-chloro-1,3-dimethoxybenzene), and a dissimilar compound, trichloroethene (TCE). The sorbents included a mineral soil (3% OM), a peat soil (93% OM), soil humic acid particles (99% OM), rubbery polymers (polyethylene, cellulose, chitin), a glassy polymer [poly(2,6-diphenyl-p-phenylene oxide)], and a mesoporous silica gel. The rubbery polymers afforded linear single-solute isotherms and no competition, both consistent with ideal (Henry's law) partition sorption. The other sorbents, including the glassy polymer, gave nonlinear single-solute isotherms and significant compet...

Book
01 Jan 1996
TL;DR: In this paper, the authors present a historical overview of Soils and the Fitness of the Soil Environment, including primary production processes in Soils: Roots and Rhizosphere Associates, secondary production: Activities and Functions of Heterotrophic Organisms--Microbes, and the soil Fauna.
Abstract: Preface to First Edition Preface to Second Edition 1 Historical Overview of Soils and the Fitness of the Soil Environment 2 Primary Production Processes in Soils: Roots and Rhizosphere Associates 3 Secondary Production: Activities and Functions of Heterotrophic Organisms--Microbes 4 Secondary Production: Activities and Functions of Heterotrophic Organisms--The Soil Fauna 5 Decomposition and Nutrient Cycling 6 Soil Foodwebs: Detritivory and Microbivory in Soils 7 Soil Biodiversity, and Linkages to Soil Processes 8 Future Developments in Soil Ecology 9 Laboratory and Field Exercises in Soil Ecology

01 Jan 1996
TL;DR: Barrie and Prosser as mentioned in this paper used Gas Isotope Ratio Mass Spectrometry (GIRMS) for automated analysis of light-element Stable Isotopes.
Abstract: ...Gas Isotope Ratio Mass Spectrometry Automated Analysis of Light-Element Stable Isotopes by Isotope Ratio Mass Spectrometry, Andrew Barrie and Simon J. Prosser Stable Carbon Isotope Ratios of Soil Organic Matter and Their Use as Indicators of Vegetation and Climate Change, Thomas W. Boutton Measurement of Soil Organic Matter Turnover Using 13C Natural Abundance, Jerome Balesdent and Andre Mariotti Stable Carbon and Oxygen Isotopes in Soil CO2 and Soil Carbonate: Theory, Practice, and

Journal ArticleDOI
TL;DR: More than 30 years have passed since the first application of nuclear magnetic resonance (NMR) spectroscopy to soil organic matter (SOM), and there has been an explosion of applications using 1H, 13C, 31P, and 15N NMR on both solution and solid-state samples as discussed by the authors.
Abstract: More than 30 years have passed since the first application of nuclear magnetic resonance (NMR) spectroscopy to soil organic matter (SOM). Since then, there has been an explosion of applications using 1H, 13C, 31P, and 15N NMR on both solution and solid-state samples. These have greatly enhanced our

Book
30 Dec 1996
TL;DR: In this paper, the Carbon Balance of Forests and Nutrient Distribution and Cycling are discussed in the context of modern technology and ecophysiology to forest management, with a focus on tree-water relations.
Abstract: Introduction: Forests in the Modern World. Forest Biomes of the World. Canopy Architecture and Microclimate. Forest Hydrology and Tree-Water Relations. The Carbon Balance of Forests. Soil Organic Matter and Decomposition. Nutrient Distribution and Cycling. Changes in Ecosystem Structure and Function During Stand Development. Ecosystem Process Models. Applications of Modern Technology and Ecophysiology to Forest Management.

Journal ArticleDOI
TL;DR: In this paper, the turnover and inputs of organic C in water-stable aggregates of different sizes were investigated, showing that the formation and degradation of microaggregates may be more dynamic than is predicted by their stability in cultivated soils or by the observed turnover times for old C.
Abstract: A major factor controlling soil organic matter dynamics is believed to be the differing degrees of protection from decomposition afforded by the spatially hierarchical organization of soil aggregate structure Changes in the natural 13 C content and in the concentration of soil organic C resulting from the growth of C3 pasture grasses (low δ 13 C PDB ) on former C4 cropland (high δ 13 C PDB ) were used to investigate the turnover and inputs of organic C in water-stable aggregates of different sizes After removal of free and released particulate organic matter (POM) in aggregate size separates (POM with a density ≤185 g cm -3 that was either exterior to aggregates in situ or released from unstable aggregates by slaking), organic C concentrations were greater in macroaggregates (>212 μm) than in microaggregates (53-212 μm) The turnover time (1/k) for C4-derived C was 412 yr for microaggregates, compared with an average turnover of 140 yr for macroaggregates, indicating that old C associated with microaggregates may be both biochemically recalcitrant and physically protected Net input rates of C3-derived C increased with aggregate size (073-113 g kg -1 yr -1 ), supporting the concept of an aggregate hierarchy created by the binding of microaggregates into increasingly larger macroaggregates The net input rate for microaggregates, however, was equal to the rates for small macroaggregates, suggesting that the formation and degradation of microaggregates may be more dynamic than is predicted by their stability in cultivated soils or by the observed turnover times for old C

01 Jan 1996
TL;DR: In this article, the authors evaluate the suitability of SOM models for evaluating the likely effectiveness of different mitigation options. But, since changes in SOM occur slowly, long-term datasets are required.
Abstract: Soil organic matter (SOM) represents a major pool of carbon within the biosphere, roughly twice than in atmospheric CO2. SOM models embody the best understanding of soil carbon dynamics and are needed to predict how global environmental change will influence soil carbon stocks. These models are also required for evaluating the likely effectiveness of different mitigation options. The first important step towards systematically evaluating the suitability of SOM models for these purposes is to test their simulations against real data. Since changes in SOM occur slowly, long-term datasets are required. This volume examines SOM models using long-term datasets from diverse ecosystems, land uses and climatic zones within the temperate region.



Journal ArticleDOI
01 Jul 1996-Ecology
TL;DR: In this paper, the authors studied plant survival and colonization over an experimental gradient, from fire lightly scorching the soil to fire consuming most of the organic soil layer, at two forest sites in northern Sweden.
Abstract: We studied plant survival and colonization over an experimental gradient, from fire lightly scorching the soil to fire consuming most of the organic soil layer, at two forest sites in northern Sweden. The gradient was achieved by adding different amounts of fuel to small plots that were burned in 1988 and 1989. Temperature was recorded at four soil strata during burning. We analyzed survival of seeds and rhizomes in the soil immediately after fire, and followed vegetation cover and seedling establishment until 1993. During fire, there was a steep decline in maximum temperature with increasing depth below the char, irrespective of the depth of burn in the mor layer, indicating that burn depth can be used as a general indicator of heat impact below ground. Lethal temperature was not recorded deeper than 20-30 mm under the burn boundary. Plant survival was determined both by depth of burn and by depth distribution of regenerative structures in the soil. Three rhizomatous species, the dwarf shrubs Vaccinium myrtillus and Vaccinium vitis-idaea and the grass Deschampsia fiexuosa, were dominant in the prefire vegetation. For all three species, the bulk of the soil bud bank was located within the mor layer, but was more superficial for D. flexuosa. Initial mortality in the bud bank was progressively higher with increasing depth of burn, and this determined the regrowth over the following years. After fires that consumed only the moss layer, cover of the Vaccinium species returned to prefire levels within 2-4 yr, and D. fiexuosa showed a dramatic increase in cover as well as in fruiting. Fires that burned slightly deeper nearly eliminated D. flexuosa, and the deepest burning fires also eliminated Vaccinium s-pp. In contrast to regrowth from rhizomes, col- onization from seed was better after relatively deep-burning fire, both for species with a soil seed bank and for species dispersing seed onto the burnt soil. However, after fires consuming most of the organic soil layer, seed bank species were also badly affected, whereas dispersers showed progressively better establishment with increasing depth of burn. Differences between treatments were still great after 5 yr, indicating that variation in depth of burn will have a long-lasting impact on the vegetation. These results from ex- perimentally burned plots were corroborated by an analysis of depth distribution of viable plant rhizomes and seeds, and the initial colonization at a site newly burned in a wildfire. The precise response patterns of boreal vegetation to variation in burn depth will depend on characteristics of the species present. However, we assume that these results have a high degree of generality, since, in podzolized soils, most rhizomatous species are predominantly located in the mor layer, since the dormant seed bank typically is concentrated at the interface of mor and mineral soil, and also since a thick organic soil layer is a poor seedbed for incoming seeds. The results indicate that in boreal forest, depth of burn is a more important variable than fire front intensity for the understory vegetation, in contrast to the situation in ecosystems with little accumulation of organic material on the mineral soil.

Journal ArticleDOI
01 Mar 1996-Geoderma
TL;DR: In this paper, the consequences of deforestation and pasture establishment for soil chemical and physical properties and for soil organic matter content, in Rondonia, in the southwestern part of the Brazilian Amazon basin, were examined.

Journal ArticleDOI
TL;DR: The results indicate that biodegradation of hydrocarbons in the rhizosphere is stimulated by plant roots, and elimination of pollutants was accompanied by an increase in microbial numbers and activities.

Book ChapterDOI
31 Dec 1996
TL;DR: In this paper, primary production and soil microbial activity are recognized as the overall biological processes governing soil organic C (SOC) dynamics, and hence, SOC cycling and storage are controlled by complex underlying biotic and abiotic interactions and feedbacks, most of which can be tied in one way or another to the influences of the five state factors related to soil formation.
Abstract: Primary production (specifically, the rate and quality of C transfer below ground) and soil microbial activity (specifically, the rates of C transformation and decay) are recognized as the overall biological processes governing soil organic C (SOC) dynamics These two processes and, hence, SOC cycling and storage are controlled by complex underlying biotic and abiotic interactions and feedbacks, most of which can be tied in one way or another to the influences of the five state factors related to soil formation, and many of which are sensitive to management practices Overall, C input rates and quality are largely dependent on climate (especially temperature and precipitation), vegetation type and landscape, soil type, and management practices Decomposition processes and turnover rates, however, are greatly influenced by climate, the type and quality of organic matter (eg, N content and the ratios of C:N and lignin:N), chemical or physicochemical associations of organic matter (OM) with soil mineral components, and the location of OM within the soil

Book
01 Jan 1996
TL;DR: In this article, the authors discuss the physical and mechanical characteristics of New Zealand soils and the storage of water in soil and water and solute movement in soils and plants, as well as the management of soil physical conditions.
Abstract: List of plates Foreword Acknowledgments 1. The soil profile 2. Soil formation 3. Classification and characteristics of New Zealand soils 4. Soil pattern, soil mappings, soil maps and their interpretation 5. The physical and mechanical characteristics of soils 6. The storage of water in soil 7. Water and solute movement in soils and plants 8. Soil aeration and temperature 9. Management of soil physical conditions 10. Soil organic matter 11. Inorganic soil colloids 12. Ion exchange in soils and soil acidity 13. Nutrient availablity 14. Soil, plant and fertiliser nitrogen 15. Soil, plant and fertiliser phosphorus 16. Soil, plant and fertiliser sulphur 17. Potassium, calcium , magnesium and sodium 18. Micronutrients 19. Soil fertility and fertiliser management 20. Additional management considerations for horticultual and forestry soils 21. Soils and the quality of the environment

Book ChapterDOI
01 Jan 1996
TL;DR: In this article, the role of the dissolved organic material (DOM) in the unsaturated zone and the surface aquatic ecosystems is discussed. And the potential ecological function and in situ availability of the DOM are considered so that one can understand and predict its environmental role.
Abstract: Publisher Summary Humus is defined as being synonymous with soil organic matter, which in turn is the total organic matter in a soil exclusive of the biomass and undecayed material Dissolved humus consists of the dissolved organic material (DOM) in soil, which influences the overall ecology and geochemistry of soil This chapter focuses on the DOM's ecological role in the unsaturated zone, with the saturated zone and the surface aquatic ecosystems being peripherally considered The relation of the DOM to other ecological components in soil is influenced by two types of fluxes The first one is physical diffusion The DOM diffuses over a concentration gradient The second physical flux is convection, which is dependent on a gradient in the soil's water content as a result of precipitation The dissolved humus is mobile and so it can be fully available theoretically This mobility and availability is not constant; it can vary both over space and time The potential ecological function and in situ availability of the dissolved humus are considered in the chapter so that one is able to understand and predict its environmental role


Journal ArticleDOI
TL;DR: In this paper, the effects of fertilization on soil organic matter turnover and storage of residue C under continuous corn were evaluated using soils from a long-term field experiment in Ontario.
Abstract: Soil organic matter turnover is influenced by N ; thus long-term fertilization of corn (Zea mays L.) may significantly affect soil organic matter levels. Effects of fertilization on soil organic matter turnover and storage of residue C under continuous corn were evaluated using soils from a long-term field experiment in Ontario. Total organic C and natural 13 C abundance measurements indicated that fertilized soils had more organic C than unfertilized soils, the difference accounted for by more C 4 -derived C in the fertilized soils. About 22 to 30% of the soil C in the plow layer had turned over and was derived from corn in the fertilized soils ; in unfertilized soils only 15 to 20% was derived from corn. Assuming that organic matter turnover follows first-order kinetics, the half-life of C 3 -derived C in the surface 10 cm of both soils was the same, about 19 yr. Natural 13 C abundance measurements and estimates from a soil organic matter model indicate that 10 to 20% of the added residue C was retained in the soil. Fertilized soils had more light fraction (LF) C than unfertilized soils. More than 70% of the C in the LF of fertilized soils was derived from corn ; in unfertilized soils only 41% was derived from corn. The half-life of C 3 -derived C in the LF was shorter than 10 yr. These results indicate that adequate fertilization increases crop yields, in turn leading to greater C storage, and that fertilization does not significantly alter the rate of turnover of native soil organic matter.

Journal ArticleDOI
TL;DR: In this paper, the authors compared long-term ( > 50 y) temperate forest and agricultural ecosystems located on the same soil type to determine if forest conversion to agriculture affects concentrations of total, water-soluble and bioavailable organic carbon (SOC) throughout the soil profile.
Abstract: When forest ecosystems are converted to agriculture, there is generally a marked decline in the amounts of total and labile soil organic carbon (SOC). However, analysis of SOC changes induced by forest conversion to agriculture have generally been restricted to surface horizons and to pools of total and microbial biomass SOC. Changes in water-soluble SOC, which is likely the most labile and mobile form of SOC, have received much less attention. We have compared concentrations of total, water-soluble (both humic and acid-soluble fractions) and bioavailable SOC beneath long-term ( > 50 y) temperate forest and agricultural ecosystems located on the same soil type. Our objectives were (1) to determine if forest conversion to agriculture affects concentrations of total, water-soluble and bioavailable SOC throughout the soil profile and (2) to determine if amounts of water-soluble and bioavailable SOC show similar patterns as total SOC. As expected, total SOC was higher in forest than in crop systems, but the difference was restricted to the surface layers. Surprisingly, concentrations of water-soluble and bioavailable SOC were higher in agricultural soils than in forest soils, again only in the surface layers. The difference in water-soluble and bioavailable SOC between agricultural and wooded soils was largely caused by an increase in the soluble humic acid fraction in the agricultural soils. Our data suggest that while agricultural soils generally have lower amounts of total and microbial C than forest soils, they may support equal or greater rates of microbial activity than forest soils due to increased production of water-soluble carbon.