As the largest pool of terrestrial organic carbon, soils interact strongly with atmospheric composition, climate, and land cover change. Our capacity to predict and ameliorate the consequences of global change depends in part on a better understanding of the distributions and controls of soil organic carbon (SOC) and how vegetation change may affect SOC distributions with depth. The goals of this paper are (1) to examine the association of SOC content with climate and soil texture at different soil depths; (2) to test the hypothesis that vegetation type, through patterns of allocation, is a dominant control on the vertical distribution of SOC; and (3) to estimate global SOC storage to 3 m, including an analysis of the potential effects of vegetation change on soil carbon storage. We based our analysis on .2700 soil profiles in three global databases supplemented with data for climate, vegetation, and land use. The analysis focused on mineral soil layers. Plant functional types significantly affected the vertical distribution of SOC. The per- centage of SOC in the top 20 cm (relative to the first meter) averaged 33%, 42%, and 50% for shrublands, grasslands, and forests, respectively. In shrublands, the amount of SOC in the second and third meters was 77% of that in the first meter; in forests and grasslands, the totals were 56% and 43%, respectively. Globally, the relative distribution of SOC with depth had a slightly stronger association with vegetation than with climate, but the opposite was true for the absolute amount of SOC. Total SOC content increased with precipitation and clay content and decreased with temperature. The importance of these controls switched with depth, climate dominating in shallow layers and clay content dominating in deeper layers, possibly due to increasing percentages of slowly cycling SOC fractions at depth. To control for the effects of climate on vegetation, we grouped soils within climatic ranges and compared distributions for vegetation types within each range. The percentage of SOC in the top 20 cm relative to the first meter varied from 29% in cold arid shrublands to 57% in cold humid forests and, for a given climate, was always deepest in shrublands, inter- mediate in grasslands, and shallowest in forests ( P , 0.05 in all cases). The effect of vegetation type was more important than the direct effect of precipitation in this analysis. These data suggest that shoot/root allocations combined with vertical root distributions, affect the distribution of SOC with depth. Global SOC storage in the to p3mo fsoil was 2344 Pg C, or 56% more than the 1502 Pg estimated for the first meter (which is similar to the total SOC estimates of 1500-1600 Pg made by other researchers). Global totals for the second and third meters were 491 and 351 Pg C, and the biomes with the most SOC at 1-3 m depth were tropical evergreen forests (158 Pg C) and tropical grasslands/savannas (146 Pg C). Our work suggests that plant functional types, through differences in allocation, help to control SOC distributions with depth in the soil. Our analysis also highlights the potential importance of vegetation change and SOC pools for carbon sequestration strategies.

The vertical distribution of soil organic carbon and its relation to climate and vegetation

The relationship between soil structure and the ability of soil to stabilize soil organic matter (SOM) is a key element in soil C dynamics that has either been overlooked or treated in a cursory fashion when developing SOM models. The purpose of this paper is to review current knowledge of SOM dynamics within the framework of a newly proposed soil C saturation concept. Initially, we distinguish SOM that is protected against decomposition by various mechanisms from that which is not protected from decomposition. Methods of quantification and characteristics of three SOM pools defined as protected are discussed. Soil organic matter can be: (1) physically stabilized, or protected from decomposition, through microaggregation, or (2) intimate association with silt and clay particles, and (3) can be biochemically stabilized through the formation of recalcitrant SOM compounds. In addition to behavior of each SOM pool, we discuss implications of changes in land management on processes by which SOM compounds undergo protection and release. The characteristics and responses to changes in land use or land management are described for the light fraction (LF) and particulate organic matter (POM). We defined the LF and POM not occluded within microaggregates (53–250 μm sized aggregates as unprotected. Our conclusions are illustrated in a new conceptual SOM model that differs from most SOM models in that the model state variables are measurable SOM pools. We suggest that physicochemical characteristics inherent to soils define the maximum protective capacity of these pools, which limits increases in SOM (i.e. C sequestration) with increased organic residue inputs.

Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils

http://www.tinread.usarb.md:8888/tinread/fulltext/lal/soil_structure.pdf

Soil structure and management: a review

Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics

https://www.ipcc-nggip.iges.or.jp/public/gpglulucf/gpglulucf_files/0_Task1_Cover/Cover_TOC.pdf

Good Practice Guidance for Land Use, Land-Use Change and Forestry

SOIL SAMPLING AND HANDLING, G.T. Patterson and M.R. Carter Soil Sampling Designs, D. Pennock, T. Yates, and J. Braidek Sampling Forest Soils, N. Belanger and K.C.J. Van Rees Measuring Change in Soil Organic Carbon Storage, B.H. Ellert, H.H. Janzen, A.J. VandenBygaart, and E. Bremer Soil Sample Handling and Storage, S.C. Sheppard and J.A. Addison Quality Control in Soil Chemical Analysis, C. Swyngedouw and R. Lessard DIAGNOSTIC METHODS for SOIL and ENVIRONMENTAL MANAGEMENT, J.J. Schoenau and I.P. O'Halloran Nitrate and Exchangeable Ammonium Nitrogen, D.G. Maynard, Y.P. Kalra, and J.A. Crumbaugh Mehlich 3 Extractable Elements, N. Ziadi and T. Sen Tran Sodium Bicarbonate Extractable Phosphorus, J.J. Schoenau and I. P. O'Halloran Boron, Molybdenum and Selenium, G. M. Hettiarachchi and U. C. Gupta Trace Element Assessment, W.H. Hendershot, H. Lalande, D. Reyes, and D. MacDonald Readily Soluble Aluminum and Manganese in Acid Soils, Y.K. Soon, N. Belanger, and W.H. Hendershot Lime Requirement, N. Ziadi and T. Sen Tran Ion Supply Rates Using Ion Exchange Resins, P. Qian, J.J. Schoenau, and N. Ziadi Environmental Soil Phosphorus Indices, A.N. Sharpley, P.J.A. Kleinman and J.L. Weld Electrical Conductivity and Soluble Ions, J.J. Miller and D. Curtin SOIL CHEMICAL ANALYSES, Y.K. Soon and W.H. Hendershot Soil Reaction and Exchangeable Acidity, W.H. Hendershot, H. Laland,e and M. Duquette Collection and Characterization of Soil Solutions, J.D. MacDonald, N. Belanger, S. Sauve, F. Courchesne, and W.H. Hendershot Ion Exchange and Exchangeable Cations, W.H. Hendershot, H. Lalande, and M. Duquette Non-Exchangeable Ammonium, Y.K. Soon and B.C. Liang Carbonates, T.B. Goh and A.R. Mermut Total and Organic Carbon, J.O. Skjemstad and J.A. Baldock Total Nitrogen, P.M. Rutherford, W.B. McGill, C.T. Figueiredo, and J.M. Arocena Chemical Characterization of Soil Sulphur, C.G. Kowalenko and M. Grimmett Total and Organic Phosphorus, I.P. O'Halloran and B.J. Cade-Menum Characterization of Available P by Sequential Extraction, H. Tiessen and J.O. Moir Extractable Al, Fe, Mn, and Si, F. Courchesne and M.C. Turmel Determining Nutrient Availability in Forest Soils, N. Belanger, David Pare, and W.H. Hendershot Chemical Properties of Organic Soils, A. Karam SOIL BIOLOGICAL ANALYSES, E. Topp and C.A. Fox Cultural Methods for Soil and Root Associated Microorganisms, J.J. Germida and J.R. de Freitas Arbuscular Mycorrhiza, Y. Dalpe and C. Hamel Root Nodule Bacteria and Symbiotic Nitrogen Fixation, D. Prevost and H. Antoun Microarthropods, J.P Winter and V.M. Behan-Pelletier Nematodes, T.A. Forge and J. Kimpinski Earthworms, M.J. Clapperton, G.H. Baker and C.A. Fox Enchytraeids, S.M. Adl Protozoa, S.M. Adl, D. Acosta-Mercado, and D.H. Lynn Denitrification Techniques for Soils, C.F. Drury, D.D. Myrold, E.G. Beauchamp, and W.D.Reynolds Nitrification Techniques in Soil Systems, C.F. Drury, S.C. Hart, and X.M. Yang Substrate-Induced Respiration and Selective Inhibition as Measures of Microbial Biomass in Soils, V.L. Bailey, J.L. Smith, and H. Bolton Jr. Assessment of Soil Biological Activity, R.P.Beyaert and C.A. Fox Soil ATP, R.P. Voroney, G. Wen, and R.P. Beyaert Lipid-Based Community Analysis, K.E. Dunfield Bacterial Community Analyses by Denaturing Gradient Gel Electrophoresis (DGGE), E. Topp, Y.-C. Tien, and A. Hartmann Indicators of Soil Food Web Properties, T.A. Forge and M. Tenuta SOIL ORGANIC MATTER ANALYSES, E.G. Gregorich and M.H. Beare Carbon Mineralization, D.W. Hopkins Mineralizable Nitrogen, Denis Curtin and C.A. Campbell Physically Uncomplexed Organic Matter, E.G. Gregorich and M.H. Beare Extraction and Characterization of Dissolved Organic Matter, M.H. Chantigny, D.A. Angers, K. Kaiser, and K. Kalbitz Soil Microbial Biomass C, N, P and S, R.P. Voroney, P.C. Brookes, and R.P. Beyaert Carbohydrates, M.H. Chantigny and D.A. Angers Organic Forms of Nitrogen, D.C. Olk Soil Humus Fractions, D.W. Anderson and J.J Schoenau Soil Organic Matter Analysis by Solid-State 13C Nuclear Magnetic Resonance Spectroscopy, M. J. Simpson and C. M. Preston Stable Isotopes in Soil and Environmental Research, B.H. Ellert and L. Rock SOIL PHYSICAL ANALYSES, D.A. Angers and F.J. Larney Particle Size Distribution, D. Kroetsch and C. Wang Soil Shrinkage, C.D. Grant Soil Density and Porosity, X. Hao, B.C. Ball, J.L.B. Culley, M.R. Carter, and G.W. Parkin Soil Consistency: Upper and Lower Plastic Limits, R.A. McBride Compaction and Compressibility, P. Defossez, T. Keller and G. Richard Field Soil Strength, G.C. Topp and D.R. Lapen Air Permeability, C.D. Grant and P.H. Groenevelt Aggregate Stability to Water, D.A. Angers, M.S. Bullock, and G.R. Mehuys Dry Aggregate Size Distribution, F.J. Larney Soil Air, R.E. Farrell and J.A. Elliott Soil-Surface Gas Emissions, P. Rochette and N. Bertrand Bulk Density Measurement in Forest Soils, D.G. Maynard and M.P. Curran Physical Properties of Organic Soils and Growing Media: Particle Size and Degree of Decomposition, L.E. Parent and J. Caron Physical Properties of Organic Soils and Growing Media: Water and Air Storage and Flow Dynamics, J. Caron, D.E. Elrick, J.C. Michel, and R. Naasz SOIL WATER ANALYSES, W.D. Reynolds and G.C. Topp Soil Water Analyses: Principles and Parameters, W.D. Reynolds and G.C. Topp Soil Water Content, G.C. Topp, G.W. Parkin, and Ty P.A Ferre Soil Water Potential, N.J. Livingston and G.C. Topp Soil Water Desorption and Imbibition: Tension and Pressure Techniques, W.D. Reynolds and G.C. Topp Soil Water Desorption and Imbibition: Long Column, W.D. Reynolds and G.C. Topp Soil Water Desorption and Imbibition: Psychrometry, W.D. Reynolds and G.C. Topp Saturated Hydraulic Properties: Laboratory Methods, W.D. Reynolds Saturated Hydraulic Properties: Well Permeameter, W.D. Reynolds Saturated Hydraulic Properties: Ring Infiltrometer, W.D. Reynolds Saturated Hydraulic Properties: Auger-Hole, G.C. Topp Saturated Hydraulic Properties: Piezometer, G.C. Topp Unsaturated Hydraulic Properties: Laboratory Tension Infiltrometer, F.J. Cook Unsaturated Hydraulic Properties: Laboratory Evaporation, O.O. B. Wendroth and N. Wypler Unsaturated Hydraulic Properties: Field Tension Infiltrometer, W.D. Reynolds Unsaturated Hydraulic Properties: Instantaneous Profile, W.D. Reynolds Estimation of Soil Hydraulic Properties, F.J. Cook and H.P. Cresswell Analysis of Soil Variability, B.C. Si, R.G. Kachanoski, and W.D. Reynolds APPENDIX Site Description, G.T. Patterson and J.A. Brierley General Safe Laboratory Operation Procedures, P. St-Georges INDEX

Soil Sampling and Methods of Analysis

Soil quality is a composite measure of both a soil’s ability to function and how well it functions, relative to a specific use. Soil quality can be assessed using a minimum data set comprising soil attributes such as texture, organic matter, pH, bulk density, and rooting depth. Soil organic matter has particular significance for soil quality as it can influence many different soil properties including other attributes of the minimum data set. Assessment of soil organic matter is a valuable step towards identifying the overall quality of a soil and may be so informative as to be included in minimum data sets used to evaluate the world’s soils.In this review, soil organic matter is considered to encompass a set of attributes rather than being a single entity. Included among the attributes and discussed here are total soil organic carbon and nitrogen, light fraction and macroorganic (particulate) matter, mineralizable carbon and nitrogen, microbial biomass, soil carbohydrates and enzymes. These attributes ar...

Towards a minimum data set to assess soil organic matter quality in agricultural soils

Introduction Analysis of Soil Organic Matter Storage in Agroecosystems, M.R. Carter Mechanisms and Processes Soil Architecture and Distribution of Organic Matter, M.J. Kooistra and M. van Noordwijk Formation of Soil Aggregates and Accumulation of Soil Organic Matter, J.M. Tisdall Carbon in Primary and Secondary Organomineral Complexes, B.T. Christensen Storage of Soil Carbon in the Light Fraction and Macroorganic Matter, E.G. Gregorich and H.H. Janzen Impact of Climate, Soil Type, and Management Aggregation and Organic Matter Storage in Cool, Humid Agricultural Soils, D.A. Angers and M.R. Carter Aggregation and Organic Matter Storage in Meso-Thermal, Humid Soils, R.J. Haynes and M.H. Beare Aggregation and Organic Matter Storage in Sub-Humid and Semi-Arid Soils, R.C. Dalal and B.J. Bridge Aggregation and Organic Matter Storage in Kaolinitic and Smectitic Tropical Soils, C. Feller, A. Albrecht, and D. Tessier Organic Carbon Storage in Tropical Hydromorphic Soils, H.W. Scharpenseel, E.-M. Pfeiffer, and P. Becker-Heidmann Assessment of Soil Organic Matter Storage Conservation Strategies for Improving Soil Quality and Organic Matter Storage, D.L. Karlen and C.A. Cambardella Models to Evaluate Soil Organic Matter Storage and Dynamics, W.J. Parton, D.S. Ojima, and D.S. Schimel Methods to Characterize and Quantify Organic Matter Storage in Soil Fractions and Aggregates, M.R. Carter and E.G. Gregorich Index

Structure and Organic Matter Storage in Agricultural Soils

Soil organic matter storage capacity in agroecosystems varies with soil type, climate and agricultural management practices. The effects of different tillage systems on organic C and N storage were determined for a range of soils of eastern Canada mainly under continuous corn and small grain cereal production. Soil profiles from eight sites on which comparative tillage experiments had been performed for up to 11 years were sampled to a 60 cm depth in four increments (0–10, 10–20, 20–40 and 40–60cm). Organic C and N contents and dry bulk density were determined for each sampling depth. Bulk density measurements showed that the total soil mass in the soil profiles was not influenced by the tillage systems. No significant differences were found between tillage treatments in the total organic C and N storage down to 60 cm depth; the soil profiles under no-till (NT) and chisel plowing (CP) generally did not contain more C and N than those under conventional moldboard plowing (MP). However, the depth distribution of soil C and N varied with tillage. In the surface 0–10cm, C and N contents were higher under NT than under MP, whereas at deeper levels (20–40cm) the reverse trend was observed. It is concluded than under eastern Canadian conditions, where crop production and residue inputs are not affected by tillage, reduced tillage systems would not result in the storage of more soil organic matter in the entire soil profile at least in a 5–10 year period. Placement of the residues would be a major factor influencing the C and N distribution at specific depths.

Impact of tillage practices on organic carbon and nitrogen storage in cool, humid soils of eastern Canada

Chapter headings: Introduction. Soil Quality Attributes. Evaluating Soil Quality. Practical Applications for Soil Quality Assessment.

M.R. Carter

Papers

Soil Sampling and Methods of Analysis

Towards a minimum data set to assess soil organic matter quality in agricultural soils

Structure and Organic Matter Storage in Agricultural Soils

Impact of tillage practices on organic carbon and nitrogen storage in cool, humid soils of eastern Canada

Soil quality for crop production and ecosystem health