Showing papers on "Soil organic matter published in 1995"

Environmental Soil Chemistry

Abstract: Environmental Soil Chemistry: An Overview: Evolution of Soil Chemistry. The Modern Environmental Movement. Contaminants in Waters and Soils. Case Study of Pollution of Soils and Waters. Soil Decontamination. Inorganic Soil Components: Pauling's Rules. Primary Soil Minerals. Secondary Soil Minerals. Specific Surface of Soil Minerals. Surface Charge of Soil Minerals. Identification of Minerals by X-Ray Diffraction Analyses. Use of Clay Minerals to Retain Organic Contaminants. Chemistry of Soil Organic Matter: Effects of Soil Formation Factors on SOM Contents. Composition of SOM. Fractionation of SOM. SOM Structure. Functional Groups and Charge Characteristics. Humic Substance-Metal Interactions. SOM-Clay Complexes. Retention of Pesticides and Other Organic Substances by Humic Substances. Soil Solution-Solid Phase Equilibria: Measurement of the Soil Solution. Speciation of the Soil Solution. Ion Activity and Activity Coefficients. Dissolution and Solubility Processes. Sorption Phenomena on Soils: Introduction and Terminology. Surface Functional Groups. Surface Complexes. Adsorption Isotherms. Equilibrium-Based Adsorption Models. Surface Precipitation. Sorption of Metal Cations. Sorption of Anions. Points of Zero Charge. Desorption. Use of Spectroscopic and Microscopic Methods in Determining Mechanisms for Sorption-Desorption Phenomena. Ion Exchange Processes: Characteristics of Ion Exchange. Cation Exchange Equilibrium Constants and Selectivity Coefficients. Thermodynamics of Ion Exchange. Relationship between Thermodynamics and Kinetics of Ion Exchange. Kinetics of Soil Chemical Processes: Rate-Limiting Steps and Time Scales of Soil Chemical Reactions. Rate Laws. Determination of Reacti

The temperature dependence of soil organic matter decomposition, and the effect of global warming on soil organic C storage

Abstract: One of the key questions in climate change research relates to the future dynamics of the large amount of C that is currently stored in soil organic matter. Will the amount of C in this pool increase or decrease with global warming? The future trend in amounts of soil organic C will depend on the relative temperature sensitivities of net primary productivity and soil organic matter decomposition rate. Equations for the temperature dependence of net primary productivity have been widely used, but the temperature dependence of decomposition rate is less clear. The literature was surveyed to obtain the temperature dependencies of soil respiration and N dynamics reported in different studies. Only laboratory-based measurements were used to avoid confounding effects with differences in litter input rates, litter quality, soil moisture or other environmental factors. A considerable range of values has been reported, with the greatest relative sensitivity of decomposition processes to temperature having been observed at low temperatures. A relationship fitted to the literature data indicated that the rate of decomposition increases with temperature at 0°C with a Q10 of almost 8. The temperature sensitivity of organic matter decomposition decreases with increasing temperature, indicated by the Q10 decreasing with temperature to be about 4.5 at 10°C and 2.5 at 20°C. At low temperatures, the temperature sensitivity of decomposition was consequently much greater than the temperature sensitivity of net primary productivity, whereas the temperature sensitivities became more similar at higher temperatures. The much higher temperature sensitivity of decomposition than for net primary productivity has important implications for the store of soil organic C in the soil. The data suggest that a 1°C increase in temperature could ultimately lead to a loss of over 10% of soil organic C in regions of the world with an annual mean temperature of 5°C, whereas the same temperature increase would lead to a loss of only 3% of soil organic C for a soil at 30°C. These differences are even greater in absolute amounts as cooler soils contain greater amounts of soil organic C. This analysis supports the conclusion of previous studies which indicated that soil organic C contents may decrease greatly with global warming and thereby provide a positive feed-back in the global C cycle.

Calculation of organic matter and nutrients stored in soils under contrasting management regimes

Abstract: Assessments of management-induced changes in soil organic matter depend on the methods used to calculate the quantities of organic C and N stored in soils. Chemical analyses in the laboratory indicate the concentrations of elements in soils, but the thickness and bulk density of the soil layers in the field must be considered to estimate the quantities of elements per unit area. Conventional methods that calculate organic matter storage as the product of concentration, bulk density and thickness do not fully account for variations in soil mass. Comparisons between the quantities of organic C, N, P and S in Gray Luvisol soils under native aspen forest and various cropping systems were hampered by differences in the mass of soil under consideration. The influence of these differences was eliminated by calculating the masses of C, N, P and S in an "equivalent soil mass" (i.e. the mass of soil in a standard or reference surface layer). Reassessment of previously published data also indicated that estimates of...

Soil sampling, preparation, and analysis.

Abstract: Principles of Soil Sampling Sample Preparation Errors and Variability, and Chemical Units of Soil Analysis Methods of Soil Chemical Analysis Soil and Plant Test Determination of Soil Water Determination of Soil Texture Determination of Soil Density and Porosity Soil pH Measurement and Lime Requirement Cation Exchange Capacity and % Base Saturation Determination Determination of Macroelements Determination of Microelements Determination of Soil Organic Matter Spectrophotometry and Colorimetry Flame Photometry Infrared Spectroscopy X-Ray Diffraction Analysis Differential Thermal Analysis Scanning Electron Microscopy and Edax Nuclear Magnetic Resonance Spectroscopy Appendices: Fundamental Constants Greek Alphabet Atomic Weights of the Major Elements X-Ray Diffraction 2 D-Spacing Conversion Table US Weights and Measures International System of Units (SI) and Conversion Factors. References and Additional Readings

Soil sampling, preparation, and analysis

Abstract: Principles of Soil Sampling Sample Preparation Errors and Variability, and Chemical Units of Soil Analysis Methods of Soil Chemical Analysis Soil and Plant Test Determination of Soil Water Determination of Soil Texture Determination of Soil Density and Porosity Soil pH Measurement and Lime Requirement Cation Exchange Capacity and % Base Saturation Determination Determination of Macroelements Determination of Microelements Determination of Soil Organic Matter Spectrophotometry and Colorimetry Flame Photometry Infrared Spectroscopy X-Ray Diffraction Analysis Differential Thermal Analysis Scanning Electron Microscopy and Edax Nuclear Magnetic Resonance Spectroscopy Appendices: Fundamental Constants Greek Alphabet Atomic Weights of the Major Elements X-Ray Diffraction 2 D-Spacing Conversion Table US Weights and Measures International System of Units (SI) and Conversion Factors. References and Additional Readings

The use of microbial parameters in monitoring soil pollution by heavy metals

Abstract: Microbial parameters appear very useful in monitoring soil pollution by heavy metals, but no single microbial parameter can be used universally. Microbial activities such as respiration, C and N mineralization, biological N2 fixation, and some soil enzymes can be measured, as can the total soil microbial biomass. Combining microbial activity and population measurements (e.g., biomass specific respiration) appears to provide more sensitive indications of soil pollution by heavy metals than either activity or population measurements alone. Parameters that have some form of “internal control”, e.g., biomass as a percentage of soil organic matter, are also advantageous. By using such approaches it might be possible to determine whether the natural ecosystem is being altered by pollutants without recource to expensive and long-running field experiments. However, more data are needed before this will be possible. Finally, new applications of molecular biology to soil pollution studies (e.g., genetic fingerprinting) which may also have value in the future are considered.

Changes in soil phosphorus fractions and ecosystem dynamics across a long chronosequence in Hawaii.

Abstract: We tested the Walker and Syers (1976) conceptual model of soil development and its ecological implications by analyzing changes in soil P, vegetation, and other ecosystem properties on a soil chronosequence with six sites ranging in age from 300 yr to 4.1 x 10 6 yr. Climate, dominant vegetation, slope, and parent material of all of the sites were similar. As fractions of total P, the various pools of soil phosphorus behaved very much as predicted by Walker and Syers. HCl-extractable P (presumably primary mineral phosphates) comprised 82% of total P at the 300-yr-old site, and then decreased to 1% at the 20,000-yr-old site. Organic phosphorus increased from the youngest site to a maximum at the 150000 yr site, and then declined to the 4.1 x 10 6 yr site. Occluded (residual) P increased steadily with soil age. In contrast to the Walker and Syers model, we found the highest total P at the 150000-yr-old site, rather than at the onset of soil development, and we found that the non-occluded, inorganic P fraction persisted through to the oldest chronosequence site. Total soil N and C increased substantially from early to middle soil development in parallel with organic P, and then declined through to the oldest site. Readily available soil P, NH 4 + , and NO 3 - were measured using anion and cation exchange resin bags. P availability increased and decreased unimodally across the chronosequence. NH 4 + and NO 3 - pools increased through early soil development, but did not systematically decline late in soil development. In situ decomposition rates of Metrosideros polymorpha litter were highest at two intermediate-aged sites with high soil fertility (20000 yr and 150000 yr), and lowest at the less-fertile beginning (300 yr) and endpoint (4.1 x 10 6 yr) of the chronosequence. M. polymorpha leaves collected from these same four sites, and decomposed in a common site, suggested that leaves from intermediate-aged sites were inherently more decomposable than those from the youngest and oldest sites. Both litter tissue quality and the soil environment appeared to influence rates of decomposition directly. The highest mean soil N 2 O emissions (809 μg.m -2 .d -1 ) were measured at the 20 000-yr-old site, which also had the highest soil nitrogen fertility status. Plant communities at all six chronosequence sites were dominated primarily by M. polymorpha, and to a lesser extent by several other genera of trees and shrubs. There were, however, differences in overall vegetation community composition among the sites. Using a detrended correspondence analysis (DECORANA), we found that a high proportion of species variance among the sites (eigenvalue = 0.71) can be explained by site age and thus soil developmental stage. Overall, long-term soil development across the chronosequence largely coincides with the conceptual model of Walker and Syers (1976). How P is distributed among different organic and inorganic fractions at a given stage of soil development provides a useful context for evaluating contemporary cycling of P and other nutrients, and for determining how changes in P availability might affect diverse ecosystem processes.

Review of root dynamics in forest ecosystems grouped by climate, climatic forest type and species

Abstract: Patterns of both above- and belowground biomass and production were evaluated using published information from 200 individual data-sets. Data sets were comprised of the following types of information: organic matter storage in living and dead biomass (e.g. surface organic horizons and soil organic matter accumulations), above- and belowground net primary production (NPP) and biomass, litter transfers, climatic data (i.e. precipitation and temperature), and nutrient storage (N, P, Ca, K) in above- and belowground biomass, soil organic matter and litter transfers. Forests were grouped by climate, foliage life-span, species and soil order. Several climatic and nutrient variables were regressed against fine root biomass or net primary production to determine what variables were most useful in predicting their dynamics. There were no significant or consistent patterns for above- and belowground biomass accumulation or NPP change across the different climatic forest types and by soil order. Similarly, there were no consistent patterns of soil organic matter (SOM) accumulation by climatic forest type but SOM varied significantly by soil order—the chemistry of the soil was more important in determining the amount of organic matter accumulation than climate. Soil orders which were high in aluminum, iron, and clay (e.g. Ultisols, Oxisols) had high total living and dead organic matter accumulations-especially in the cold temperate zone and in the tropics. Climatic variables and nutrient storage pools (i.e. in the forest floor) successfully predicted fine root NPP but not fine root biomass which was better predicted by nutrients in litterfall. The importance of grouping information by species based on their adaptive strategies for water and nutrient-use is suggested by the data. Some species groups did not appear to be sensitive to large changes in either climatic or nutrient variables while for others these variables explained a large proportion of the variation in fine root biomass and/or NPP.

Structure and Organic Matter Storage in Agricultural Soils

Abstract: 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

Bottom soils, sediment, and pond aquaculture

Abstract: Preface. Symbols. Abbreviations. Atomic weights. Soils in pond aquaculture. Physical, chemical, and mineralogical properties of soils. Soil nutrients. Exchange of dissolved substances between soil and water. Soil organic matter, anaerobic respiration and oxidation-reduction. Sediment. Relationships to aquatic animal production. Pond bottom management. Pond bottom soil analyses.

Microbial community structure and pH response in relation to soil organic matter quality in wood-ash fertilized, clear-cut or burned coniferous forest soils

Abstract: Humus phospholipid fatty acid (PLFA) analysis was used in clear-cut, wood-ash fertilized (amounts applied: 1000, 2500, and 5000 kg ha−1), or prescribed burned (both in standing and clear-cut) coniferous forests to study the effects of treatments on microbial biomass and community structure. The microbial biomass (total PLFAs) decreased significantly due to the highest rate of wood-ash fertilization, clear-cutting, and the two different fire treatments when compared to control amounts. Fungi appeared more seriously reduced by these treatments than bacteria, as revealed by a decreased index of fungal:bacterial PLFAs when compared to the controls. The community structure was evaluated using the PLFA pattern. The largest treatment effect was due to burning in both areas studied, which resulted in increases in 16:1ω5 and proportional decreases in 18:2ω6. Clear-cutting and the different amounts of ash application resulted in similar changes in the PLFA pattern to the burning treatments, but these were less pronounced. Attempts to correlate the changes in the PLFA pattern to soil pH, bacterial pH response patterns (measured using thymidine incorporation), or substrate quality (measured using IR spectroscopy) were only partly successful. Instead, we hypothesize that the changes in the PLFA pattern of the soil organisms were related to an altered substrate quantity, that is the availability of substrates after the treatments.

Belowground cycling of carbon in forests and pastures of eastern Amazonia

Abstract: Forests in seasonally dry areas of eastern Amazonia near Paragominas, Para, Brazil, maintain an evergreen forest canopy through an extended dry season by taking up soil water through deep (>1 m) roots. Belowground allocation of C in these deep-rooting forests is very large (1900 g C m−2 yr−1) relative to litterfall (460 g C m−2 yr−1). The presence of live roots drives an active carbon cycle deeper than l m in the soil. Although bulk C concentrations and 14C contents of soil organic matter at >l-m depths are low, estimates of turnover from fine-root inputs, CO2 production, and the 14C content of CO2 produced at depth show that up to 15% of the carbon inventory in the deep soil has turnover times of decades or less. Thus the amount of fast-cycling soil carbon between 1 and 8-m depths (2–3 kg C m−2, out of 17–18 kg C m−2) is significant compared to the amount present in the upper meter of soil (3–4 kg C m−2 out of 10–11 kg C m−2). A model of belowground carbon cycling derived from measurements of carbon stocks and fluxes, and constrained using carbon isotopes, is used to predict C fluxes associated with conversion of deep-rooting forests to pasture and subsequent pasture management. The relative proportions and turnover times of active (including detrital plant material; 1–3 year turnover), slow (decadal and shorter turnover), and passive (centennial to millennial turnover) soil organic matter pools are determined by depth for the forest soil, using constraints from measurements of C stocks, fluxes, and isotopic content. Reduced carbon inputs to the soil in degraded pastures, which are less productive than the forests they replace, lead to a reduction in soil carbon inventory and Δ14C, in accord with observations. Managed pastures, which have been fertilized with phosphorous and planted with more productive grasses, show increases in C and 14C over forest values. Carbon inventory increases in the upper meter of managed pasture soils are partially offset by predicted carbon losses due to death and decomposition of fine forest roots at depths >1 m in the soil. The major adjustments in soil carbon inventory in response to land management changes occur within the first decade after conversion. Carbon isotopes are shown to be more sensitive indicators of recent accumulation or loss of soil organic matter than direct measurement of soil C inventories.

Fundamental Differences Between Conventional and Organic Tomato Agroecosystems in California

Abstract: In an integrated, multidisciplinary study we compared ecological characteristics and productivity of commercial farms categorized as either organic (ORG) or conventional (CNV) based on their use of synthetic fertilizers and pesticides or reliance on organic soil amendments and biological pest control. We measured belowground parameters: various soil chemical and biological properties and root disease severity; common agronomic indicators: biomass, fruit yield and insect pest damage; and community level indicators, including arthropod diversity and soil microbial activity and diversity. CNV and ORG production systems could not be distinguished based on agronomic criteria such as fruit yield and arthropod pest damage levels. However, differences were demonstrated in many soil, plant, disease, and diversity indicators suggesting that the ecological processes determining yields and pest levels in these two management systems are distinct. In particular, nitrogen mineralization potential and microbial and parasitoid abundance and diversity were higher in ORG farms. Differences between the agroecosystems were sufficiently robust to be distinguished from environmental variation and suggest that biological processes compensated for reductions in the use of synthetic fertilizers and pesticides.

Long-term effects of metals in sewage sludge on soils, microorganisms and plants

Abstract: This paper reviews the evidence for impacts of metals on the growth of selected plants and on the effects of metals on soil microbial activity and soil fertility in the long-term. Less is known about adverse long-term effects of metals on soil microorganisms than on crop yields and metal uptake. This is not surprising, since the effects of metals added to soils in sewage sludge are difficult to assess, and few long-term experiments exist. Controlled field experiments with sewage sludges exist in the UK, Sweden, Germany and the USA and the data presented here are from these long-term field experiments only. Microbial activity and populations of cyanobacteria,Rhizobium leguminosarum bv.trifolii, mycorrhizae and the total microbial biomass have been adversely affected by metal concentrations which, in some cases, are below the European Community's maximum allowable concentration limits for metals in sludge-treated soils. For example, N2-fixation by free living heterotrophic bacteria was found to be inhibited at soil metal concentrations of (mg kg−1): 127 Zn, 37 Cu, 21 Ni, 3.4 Cd, 52 Cr and 71 Pb. N2-fixation by free-living cyanobacteria was reduced by 50% at metal concentrations of (mg kg−1): 114 Zn, 33 Cu, 17 Ni, 2.9 Cd, 80 Cr and 40 Pb.Rhizobium leguminosarum bv.trifolii numbers decreased by several orders of magnitude at soil metal concentrations of (mg kg−1): 130–200 Zn, 27–48 Cu, 11–15 Ni, and 0.8–1.0 Cd. Soil texture and pH were found to influence the concentrations at which toxicity occurred to both microorganisms and plants. Higher pH, and increased contents of clay and organic carbon reduced metal toxicity considerably. The evidence suggests that adverse effects on soil microbial parameters were generally found at surpringly modest concentrations of metals in soils. It is concluded that prevention of adverse effects on soil microbial processes and ultimately soil fertility, should be a factor which influences soil protection legislation.

Total and young organic matter distributions in aggregates of silty cultivated soils

Abstract: Summary The distribution of organic matter in soil aggregates was investigated by fractionating aggregates and measuring carbon contents. The distribution of recently incorporated organic carbon was analyzed using 13C natural abundance. The soils of the experiment, which previously only had C3 vegetation, were cropped to maize, aC4 plant, for 6 or 23 years. Aggregate size distributions were determined for silty soils with different organic matter contents. Slaking-resistant macroaggregates were enriched in C as compared to dry-sieved macroaggregates or to microaggregates, and the C content increased with the size of aggregates. The δ13C value was used to calculate the amount of C3-derived and C4-derived organic carbon in the fractions. The larger carbon contents in stable macroaggregates were due to young C4-derived organic carbon (<6 or 23 years), and we concluded that young organic matter was responsible for macroaggregate stability.

Soil organic matter changes resulting from tillage and biomass production

Abstract: Because soil is a limited resource, agricultural production is dependent on improving soil quality. Improved soil quality also has an impact on water use, as high quality soil more effectively collects and stores water, reducing the need for irrigation. Intensive use of soil throughout history has led to depletion in soil quality, leading in turn to reduced yields because of the consequent reduced organic matter. Recognizing the lessons of history, scientists at research stations such as Rothamstead in England; Pendleton, Oregon; Champaign, Illinois; and Columbia, Missouri, began long-term studies on the effects of crop rotation, crop fertilization, manure additions, and residue management on the productivity and organic matter of cropped soils. In general, it was found that soil cultivation caused a decline in organic carbon content (which constitutes about half of the organic matter), or at best stabilized organic matter, even with heavy manure treatment, as long as conventional tillage continued. In the 1960s and 197Os, many investigators noted that tillage made soils more erodible, and that crop residues left on the surface were highly effective in reducing erosion. The introduction of more and …

Carbon forms and functions in forest soils.

Abstract: Based on the papers presented at the Eighth North American Forest Soils Conference; and sponsored by the Soil Science Society of America, Society of American Foresters, Canadian Institute of Forestry, and Canadian Soil Science Society. Financial support provided by USDA Forest Service-Global Climate Change Program, ITFRayonier, Inc., Packaging of America, Georgia Pacific, Container Corporation of America-Jefferson Smurfit Corporation, Champion International Corporation, International Paper Company, and University of Florida-Institute of Food and Agricultural Sciences; Gainsville, Florida, May 1993.

Terrestrial higher‐plant response to increasing atmospheric [CO2] in relation to the global carbon cycle

Abstract: Terrestrial higher plants exchange large amounts of CO2 with the atmosphere each year; c. 15% of the atmospheric pool of C is assimilated in terrestrial-plant photosynthesis each year, with an about equal amount returned to the atmosphere as CO2 in plant respiration and the decomposition of soil organic matter and plant litter. Any global change in plant C metabolism can potentially affect atmospheric CO2 content during the course of years to decades. In particular, plant responses to the presently increasing atmospheric CO2 concentration might influence the rate of atmospheric CO2 increase through various biotic feedbacks. Climatic changes caused by increasing atmospheric CO2 concentration may modulate plant and ecosystem responses to CO2 concentration. Climatic changes and increases in pollution associated with increasing atmospheric CO2 concentration may be as significant to plant and ecosystem C balance as CO2 concentration itself. Moreover, human activities such as deforestation and livestock grazing can have impacts on the C balance and structure of individual terrestrial ecosystems that far outweigh effects of increasing CO2 concentration and climatic change. In short-term experiments, which in this case means on the order of 10 years or less, elevated atmospheric CO2 concentration affects terrestrial higher plants in several ways. Elevated CO2 can stimulate photosynthesis, but plants may acclimate and (or) adapt to a change in atmospheric CO2 concentration. Acclimation and adaptation of photosynthesis to increasing CO2 concentration is unlikely to be complete, however. Plant water use efficiency is positively related to CO2 concentration, implying the potential for more plant growth per unit of precipitation or soil moisture with increasing atmospheric CO2 concentration. Plant respiration may be inhibited by elevated CO2 concentration, and although a naive C balance perspective would count this as a benefit to a plant, because respiration is essential for plant growth and health, an inhibition of respiration can be detrimental. The net effect on terrestrial plants of elevated atmospheric CO2 concentration is generally an increase in growth and C accumulation in phytomass. Published estimations, and speculations about, the magnitude of global terrestrial-plant growth responses to increasing atmospheric CO2 concentration range from negligible to fantastic. Well-reasoned analyses point to moderate global plant responses to CO2 concentration. Transfer of C from plants to soils is likely to increase with elevated CO2 concentrations because of greater plant growth, but quantitative effects of those increased inputs to soils on soil C pool sizes are unknown. Whether increases in leaf-level photosynthesis and short-term plant growth stimulations caused by elevated atmospheric CO2 concentration will have, by themselves, significant long-term (tens to hundreds of years) effects on ecosystem C storage and atmospheric CO2 concentration is a matter for speculation, not firm conclusion. Long-term field studies of plant responses to elevated atmospheric CO2 are needed. These will be expensive, difficult, and by definition, results will not be forthcoming for at least decades. Analyses of plants and ecosystems surrounding natural geological CO2 degassing vents may provide the best surrogates for long-term controlled experiments, and therefore the most relevant information pertaining to long-term terrestrial-plant responses to elevated CO2 concentration, but pollutants associated with the vents are a concern in some cases, and quantitative knowledge of the history of atmospheric CO2 concentrations near vents is limited. On the whole, terrestrial higher-plant responses to increasing atmospheric CO2 concentration probably act as negative feedbacks on atmospheric CO2 concentration increases, but they cannot by themselves stop the fossil-fuel-oxidation-driven increase in atmospheric CO2 concentration. And, in the very long-term, atmospheric CO2 concentration is controlled by atmosphere-ocean C equilibrium rather than by terrestrial plant and ecosystem responses to atmospheric CO2 concentration.

Soils in Our Environment

Abstract: 1. Soil Composition and Importance. 2. Soil Physical Properties. 3. Soil Water Properties. 4. Soil Chemical Properties. 5. Organisms and Their Residues. 6. Soil Formation and Morphology. 7. Soil Taxonomy. 8. Acidic Soils. 9. Salt-Affected Soils. 10. Plant Nutrients: Nitrogen, Phosphorus, and Potassium. 11. Calcium, Magnesium, Sulfur, and Micronutrients. 12. Soil Fertility Management. 13. Tillage Systems and Alternatives. 14. Soil Erosion. 15. Water Resources and Irrigation. 16. Wetlands and Land Drainage. 17. Pollution of Soil, Water, and Air. 18. Toward Environmental Integrity. 19. Soil Surveys and Land-Use Planning. 20. Greenhouse Soils and Soilless Culture.

Soils and Global Change

Abstract: World Soils and Greenhouse Effect: An Overview, R Lal, J Kimble, E Levine, C Whitman Global Carbon and Nitrogen Reserves An Overview of the Carbon Cycle, WH Schlesinger Global Soil Carbon Resources, H Eswaran, E Van den Berg, P Reich, and J Kimble Changes in the Storage of Terrestrial Carbon Since 1850, RA Houghton Carbon Storage in Landfills, J Bogner and K Spokas Areal Evaluation of Organic and Carbonate Carbon in a Desert Area of Southern New Mexico, RB Grossman, RJ Ahrens, LH Gile, CE Montoya, and OA Chadwick Carbon Storage in Tidal Marsh Soils, MC Rabenhorst Spatial Modeling Using Partially Saptial Data, RB Jackson IV, AL Rowell, and KB Weinrich Soil Processes and Gaseous Emissions Effect of Global Change on Carbon Storage in Cold Soils, WC Oechel and GL Vourlitis Global Soil Erosion by Water and Carbon Dynamics, R Lal Gaseous Emissions from Agro-Ecosystems in India, IP Abrol Methane Emission from Canadian Peatlands, TR Moore and NT Roulet Decomposition of Organic Matter and Carbon Emissions from Soils, DW Anderson Factors Affecting Gaseous Emissions CO2 and CO Flux Impact of Fall Tillage on Short-Term Carbon Dioxide Flux, DC Reicosky and MJ Lindstrom Organic Matter Inputs and Methane Emissions from Soils in Major Rice Growing Regions of China, JS Kern, D Bachelet, and M Toig Soil CO2 Flux in Response to Elevated Atmospheric CO2 and Nitrogen Fertilization: Patterns and Methods, JM Vose, KJ Elliott, and DW Johnson Soils Respiration and Carbon Dynamics in Parallel Native and Cultivated Ecosystems, GA Buyanovsky, and GH Wagner NOxFlux Biosphere-Atmosphere Exchange of Gaseous N Oxides, GL Hutchinson Nitrous Oxide Flux from Thawing Soils in Alberta, JW Laidlaw, M Nyborg, and RC Izaurralde CH4 Flux Methane production in Mississippi Deltaic Plain Wetland Soils As a Function of Soil Redox Species, CR Crozier, RD DeLaune, and WH Patrick, Jr Monitoring and Assessment Soil Survey and GIS Role of Soil Survey in Obtaining a Global Carbon Budget, RW Arnold Methods to Assess Soil Carbon Using Remote Sensing Techniques, CJ Merry and ER Levine Preparing a Soil Carbon Inventory for the United States using Geographic Information Systems, NB Bliss, SW Waltman, and GW Peterson Analytical Techniques Establishing the Pool Sizes and Fluxes in CO2 Emissions from Soil Organic Matter Turnover, EA Paul, WR Horwath, D Harris, R Follett, SW Leavitt, BA Kimball, and K Pregitzer Fractionation and Carbon Balance of Soil Organic Matter In Selected Cryic Soils in Alaska, CL Ping, CJ Michaelson, and RL Malcolm Fractionation Characterization, and Comparison Of Bulk Soil Organic Substances and Water Soluble Soil Interstitial Organic Constituents in Selected Cryosols of Alaska, RL Malcolm, K Kennedy, CL Ping, and GT Michaelson CO2 Efflux from Coniferous Forest Soils: Comparison Of Measurement Methods and Effects of Added Nitrogen, KG Mattson In Search of Bioreactive Soil Organic Carbon: The Fractionation Approaches, HH Cheng and JAE Molina The Use of 13C Natural Abundance to Investigate the Turnover of the Microbial Biomass and Active Fractions of Soil Organic Matter under Two Tillage Treatments, MC Ryan, R Aravena, and RW Gillham Climatic Approach Trace Gas and Energy Fluxes: Micrometeorological Perspectives, SB Verma, J Kim, RJ Clement, NJ Shurpali, and DP Billesbach A micrometeorological Technique for Methane Flux Determination from A Field Treated with Swine Manure, JH Prueger, TB Parkin, and JJ Hatfield Modeling Application of Century Soils Organic Matter Model to a Field Site in Lexington, KY, AS Patwardham, RV Chinnaswamy, AS Donigian, Jr, AK Metherell, RL Blevins, WW Frye, and K Paustian The Exchange of Carbon Dioxide between the Atmosphere and the Terrestrial Biosphere in Latin America, CGM Klein Goldewijk and M Vloedbed Modeling the Dynamics of Organic Carbon in a Typic Haplorthod, MR Hoosbeek and RB Bryant Research and Development Priorities Towards Improving the Global Data Base on Soil Carbon, R Lal, J Kimble, E Levine, and C Whitman

Surface disturbances : their role in accelerating desertification

Abstract: Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.

Soil Organic Matter Recovery in Semiarid Grasslands: Implications for the Conservation Reserve Program

Abstract: Although the effects of cultivation on soil organic matter and nutrient supply capacity are well understood, relatively little work has been done on the long-term recovery of soils from cultivation. We sampled soils from 12 locations within the Pawnee National Grasslands of northeastern Colorado, each having native fields and fields that were his- torically cultivated but abandoned 50 yr ago. We also sampled fields that had been cultivated for at least 50 yr at 5 of these locations. Our results demonstrated that soil organic matter, silt content, microbial biomass, po- tentially mineralizable N, and potentially respirable C were significantly lower on cultivated fields than on native fields. Both cultivated and abandoned fields also had significantly lower soil organic matter and silt contents than native fields. Abandoned fields, however, were not significantly different from native fields with respect to microbial biomass, po- tentially mineralizable N, or respirable C. In addition, we found that the characteristic small-scale heterogeneity of the shortgrass steppe associated with individuals of the dom- inant plant, Bouteloua gracilis, had recovered on abandoned fields. Soil beneath plant canopies had an average of 200 g/m2 more C than between-plant locations. We suggest that 50 yr is an adequate time for recovery of active soil organic matter and nutrient availability, but recovery of total soil organic matter pools is a much slower process. Plant population dynamics may play an important role in the recovery of shortgrass steppe ecosystems from disturbance, such that establishment of perennial grasses determines the rate of organic matter recovery.

Carbon Isotope Dynamics During Grass Decomposition and Soil Organic Matter Formation

Abstract: We analyzed changes in the stable C isotope composition (s3'C) of bulk tissues and lignin fractions during a 2-yr decomposition study in east-central Minnesota (USA) of aboveground and belowground litter from four perennial grass species: Schiza- chyrium scoparium (C4), Agropyron repens (C3), Poa pratensis (C3), and Agrostis scabra (C3). Although lignin concentrations increased for all litter types during decomposition and lignin fractions were consistently depleted in '3C compared to bulk tissues (3.6%o more negative on average), we found neither convergence of bulk tissue sl3C values towards lignin s13C values, nor greater stability of sl3C values for lignin fractions. Furthermore, s'3C values of C3 and C4 species shifted in opposite directions during decomposition. Thus, our data do not support the hypothesis that s'3C values decrease during decomposition because of the selective preservation of lignin and we instead suggest that isotopic shifts are caused by the incorporation of new C from soil organic matter into litter by microbial decomposers. We estimate that this new C comprised 12-19% of the total litter C, depending on species, at the point of 70% mass loss. In monocultures of these four species plus another C4 grass (Andropogon gerardi) growing on initially homogeneous soils with a predominantly C3 isotopic signature, soil s'3C values increased 1.6-2.2%o for the C4 species and remained relatively unchanged for the C3 species after 4 yr. Averaging across the C4 species and the experimental soil organic matter gradient, 14% of the total soil C in these plots must be new C4 C to account for this isotopic shift. We estimate that this amount of new soil C equals 30% of NPP summed over 4 yr in these plots.

Microbial characteristics of soil quality

Abstract: We all recognize the rich smell of newly plowed earth, and the friable structure and deep color of healthy soil (Figure 1). We can readily contrast that to the off smell and mottled color of a low quality soil. Descriptive properties such as color, smell, and feel can easily distinguish different soils, but they may not identify subtle changes that occur in soil as a result of various management practices. Soil quality is an emerging concept that can integrate descriptive and analytical measurements of the physical, chemical, and biological components of the soil. Minor differences in these components may be early warning signals of soil degradation and can be used as indicators so that degrading effects can be remedied and soil building practices can be implemented. Analytical techniques are therefore needed to more fully differentiate soil building practices from those that are degrading. Soil microbial parameters, an integral part of soil, may be helpful as early warning signals of changes in soil quality. Soil quality Soil quality has been defined as ‘the capacity of a soil to function …

Role of Metal-Organic complexation in metal sorption by Soils

Abstract: Publisher Summary This chapter focuses on the nature of interaction among trace metals in soil solution, dissolved organics in soil solution, and solid surfaces. The interaction between metal cations and dissolved polyfunctional organic compounds of low molecular weight is important because of its role in mineral-weathering and soil-forming processes and its potential role in heavy metal contamination of soil and groundwater. The chapter presents the organics and metals in the soil solution. Dissolved organics that interact with soil constituents and trace metal ions are of two major kinds: a range of low-molecular-weight organic acids—including polyphenols, simple aliphatic acids, amino acids, sugar acids, and hydroxamate siderophores; and a series of soluble humic/fulvic acids. Numerous environmental issues arise in relation to the interaction of metal ions with soluble organics. Some of these include the phytoavailability of metals, plant nutrient availability, toxicological effects of coordinated metal ions on aquatic and marine organisms, and transport of contaminants, particularly in relation to implications for surface and groundwater quality and soil genesis. All of these issues are highly dependent on the nature and concentration of the contaminant in the soil solution phase. Extant research indicates that low-molecular-weight ligands in soil solution may either enhance or retard reactions with solid surfaces—depending on the functional groups on the organic molecule, soil surface properties, and soil solution conditions. It is imperative that increased research efforts be devoted to evaluating the effects of these organics on metal reactions in the soil.

Soil organic matter dynamics along gradients in temperature and land use on the Island of Hawaii

Abstract: We studied soil organic matter (SOM) dynamics in allophanic soils (Udands) along independent gradients of temperature (altitude) and land use (forest-pasture) on the island of Hawaii. Using an integrated '3C signal derived from land conversion along with measurements of soil respiration and soil carbon, we separated rapid, intermediate, and very slow turnover SOM pools, and estimated turnover times for the large intermediate pool. These estimates were compared to independent estimates using either bomb-derived soil 14C or the Century soil organic matter model. All calculations based on a three-pool SOM structure yield rates of turnover that are 3 times slower than those produced by a single pool model. Accordingly, analyses of potential feedbacks between changes in climate, atmospheric C02, and soil carbon should incorporate the heterogeneous nature of soil organic matter. We estimate that roughly three-quarters of the carbon in the top 20 cm of these soils has turnover times less than 30 yr. Turnover times for intermediate SOM double with a 10'C change in mean annual temperature, suggesting that recalcitrant pools of SOM may be as sensitive to changes in temperature as the smaller labile pools.

Effects of soil compaction and tillage systems on uptake and losses of nutrients

Abstract: In the framework of research on the environmental consequences of soil compaction, the impact of soil compaction and tillage systems on uptake and losses of nutrients, in particular nitrogen, are discussed. Evidence is presented to indicate interactive relationships between the amount of soil compaction, root growth, soil water and soil aeration status, and nutrient supply and uptake by plants. The importance of soil structure and pore size distribution in influencing the transport of nutrients in compacted soil is illustrated. Emphasis is given to the negative effects of soil compaction on components of the environment due to nutrient leaching, surface runoff and gaseous losses to the atmosphere.

Subsoil amelioration by plant roots : the process and the evidence

Abstract: Actively growing plant root systems have the potential to ameliorate subsoil in poor physical condition (biological drilling). Studies in which improved crop growth has been attributed to biological drilling by previous crops are reviewed. Whilst we might expect that plants are able to modify subsoil pore size distribution and that subsequent crops will benefit from the improved structure, this has yet to be demonstrated. Improvements in root growth, water extraction and grain yield do not, on their own, definitively establish the occurrence or benefits of biological drilling. Firstly, specific measurements of soil pores, their size, number and continuity are required to establish that soil structural change occurs through biological drilling. Secondly, the effects of biological drilling must be isolated from other confounding influences such as disease reduction and improvements in plant nutrition that might occur from crop rotation. The expected benefits from biological drilling might not eventuate where roots are unable to function efficiently in large pores or are unable to exit from them into the soil matrix. Model approaches can extend site and season specific observations and link soil structural changes to soil-plant-water processes, thus improving assessment of the consequences of biological drilling. Results are presented from an investigation into biological drilling by canola (Brassica napus L.) and the subsequent benefits to following wheat crops. Two seasons of canola did not create any measurable changes to soil structure at the top of the B horizon of a red brown earth (Natric Palexeralf) at Temora, N.S.W., even though grain yield and water extraction were greater for wheat following canola compared with wheat following wheat (probably due to reduced incidence of root disease). The canola appeared unable to create new pores due to the high strength of the soil matrix, and thus relied on the pre-existing pores. This, and other studies, tend to indicate that tap rooted annual crops such as lupins or canola are unlikely to be able to improve B-horizon porosity in dense, duplex soil. Perennial species (e.g. lucerne [Medicago sativa]) might be more effective at biological drilling because of the longer time and wider range of water content conditions in which to establish a deep root system. It remains to clearly demonstrate biological drilling as an effective process for ameliorating these dense subsoils.

Soil organic carbon, microbial biomass and CO2-C production from three tillage systems

Abstract: Organic matter is a major soil component which is influenced by tillage. This paper quantifies the effect of no-till, chisel tillage and plow tillage on the content and depth distribution of organic carbon and microbial biomass after 12 years of each tillage system. The soil was typical of the Argentine Rolling Pampa. The resistance of organic matter to mineralization was evaluated by means of an incubation test. In the no-till and chisel tillage systems, crop debris accumulated within the top 5 cm of soil, especially in the no-till system. Consequently, organic carbon was 42–50% higher (P=0.01) in the no-till soil than in the soil from the plow and chisel tillage systems. Biomass carbon and soil basal respiration (0–10 day period) were noticeably stratified under no-till and chisel tillage, while they were uniform from 0 to 15 cm in the plowed soil. The metabolic quotient of the biomass (basal respiration/biomass) was regulated in all cases by the coarse plant debris content of the soil (r2=0.79, P=0.01). A doubled exponential model was fitted to CO2-C values produced during 160 days of incubation (r2≥0.95). Thisshows that soil carbon dynamics can be described as being composed of two pools: one labile, and one resistant to microbial attack. The proportion of total carbon mineralized and the decomposition of soil-resistant carbon in 160 days in the no-till and chisel tillage soils were high at the soil surface, but decreased with depth. In plowed soil, these parameters were constant from 0 to 20 cm. The organic matter at the soil surface under the no-till and chisel tillage systems was more readily degradable than under plow tillage in the laboratory experiment. Carbon inputs from crops were estimated to be similar between tillage systems. Consequently, in situ accumulation of labile forms of organic matter under a no-till system may be ascribed to a decrease in the mineralization intensity of the soil organic matter. Soil temperature determinations suggested that plowed plots were warmer than no-tilled plots, and this phenomenon could lead to a decrease of microbial respiration in straw-covered soil.