Rapid turnover of organic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal as affected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties and surface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO2. Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Several research needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal.

http://www.css.cornell.edu/faculty/lehmann/publ/BiolFertSoils%2035,%20219-230,%202002%20Glaser.pdf

Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review

Summary
Mechanisms for C stabilization in soils have received much interest recently due to their relevance in the global C cycle. Here we review the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils: (i) selective preservation due to recalcitrance of OM, including plant litter, rhizodeposits, microbial products, humic polymers, and charred OM; (ii) spatial inaccessibility of OM against decomposer organisms due to occlusion, intercalation, hydrophobicity and encapsulation; and (iii) stabilization by interaction with mineral surfaces (Fe-, Al-, Mn-oxides, phyllosilicates) and metal ions. Our goal is to assess the relevance of these mechanisms to the formation of soil OM during different stages of decomposition and under different soil conditions. The view that OM stabilization is dominated by the selective preservation of recalcitrant organic components that accumulate in proportion to their chemical properties can no longer be accepted. In contrast, our analysis of mechanisms shows that: (i) the soil biotic community is able to disintegrate any OM of natural origin; (ii) molecular recalcitrance of OM is relative, rather than absolute; (iii) recalcitrance is only important during early decomposition and in active surface soils; while (iv) during late decomposition and in the subsoil, the relevance of spatial inaccessibility and organo-mineral interactions for SOM stabilization increases. We conclude that major difficulties in the understanding and prediction of SOM dynamics originate from the simultaneous operation of several mechanisms. We discuss knowledge gaps and promising directions of future research.

Stabilization of organic matter in temperate soils: mechanisms and their relevance under different soil conditions – a review

The use of equilibrium expressions for sorption to natural particles in fate and transport models is often invalid due to slow kinetics. This paper reviews recent research into the causes of slow sorption and desorption rates at the intraparticle level and how this phenomenon relates to contaminant transport, bioavailability, and remediation. Sorption kinetics are complex and poorly predictable at present. Diffusion limitations appear to play a major role. Contending mechanisms include diffusion through natural organic matter matrices and diffusion through intraparticle nanopores. These mechanisms probably operate simultaneously, but the relative importance of each in a given system is indeterminate. Sorption shows anomalous behaviors that are presently not well explained by the simple diffusion models, including concentration dependence of the slow fraction, distributed rate constants, and kinetic hysteresis. Research is needed to determine whether adsorption/desorption bond energies may play a role alon...

Mechanisms of Slow Sorption of Organic Chemicals to Natural Particles

The combined adsorption and partition effects of biochars with varying fractions of noncarbonized organic matter have not been clearly defined. Biochars, produced by pyrolysis of pine needles at different temperatures (100-700 degrees C, referred as P100-P700), were characterized by elemental analysis, BET-N2 surface areas and FTIR. Sorption isotherms of naphthalene, nitrobenzene, and m-dinitrobenzene from water to the biochars were compared. Sorption parameters (N and logKf) are linearly related to sorbent aromaticities, which increase with the pyrolytic temperature. Sorption mechanisms of biochars are evolved from partitioning-dominant at low pyrolytic temperatures to adsorption-dominant at higher pyrolytic temperatures. The quantitative contributions of adsorption and partition are determined by the relative carbonized and noncarbonized fractions and their surface and bulk properties. The partition of P100-P300 biochars originates from an amorphous aliphatic fraction, which is enhanced with a reduction of the substrate polarity; for P400-P600, the partition occurs with a condensed aromatic core that diminishes with a further reduction of the polarity. Simultaneously, the adsorption component exhibits a transition from a polarity-selective (P200-P400) to a porosity-selective (P500-P600) process, and displays no selectivity with P700 and AC in which the adsorptive saturation capacities are comparable to predicted values based on the monolayer surface coverage of molecule.

Transitional Adsorption and Partition of Nonpolar and Polar Aromatic Contaminants by Biochars of Pine Needles with Different Pyrolytic Temperatures

The flow of homogeneous fluids through porous media: analogies with other physical problems

Sorption of nonionic compounds is strongly dependent on the content as well as the nature of the organic matter in soils and sediments. The composition and the structure of organic matter varies due to its origin and geological history and strongly influences the sorption affinity for nonionic organic compounds. Organic matter in unweathered shales and high-grade coals shows enhanced sorption (> 1 order of magnitude) compared to organic matter in recent soils or geologically young material and low-grade coals. The results obtained indicate a decrease in sorption with increasing proportions of oxygen-containing functional groups in natural organic substances. A first approximation to estimate sorption coefficients for various organic matter is provided by an empirical correlation between the hydrogen/oxygen (H/O) atomic ratio as an index of the oxidation of the organic matter and the organic carbon normalized sorption coefficients (K{sub OC}). This approximation also permits adjustment of K{sub OC} values derived from K{sub OW} data.

Influence of organic matter from soils and sediments from various origins on the sorption of some chlorinated aliphatic hydrocarbons: implications on KOC correlations.

Foreword. Notation. 1: Introduction.1.1. Persistence of Organic Contaminants in the Subsurface Environment. 1.2. Nonequilibrium Transport - Remediation of Contaminated Sites. 1.3. Diffusion in Sediments and Rocks. 2: Basics of Sorption and Diffusion in Soils and Sediments. 2.1. Sorption of Organic Compounds in Soils and Sediments. 2.2. Mass Transfer by Diffusion. 3: Modeling of Diffusion Processes. 3.1. Intraparticle Diffusion. 3.2. Diffusion into Layers of Low Permeability. 4: Measured Diffusion Coefficients. 4.1. Time-Lag Experiments. 4.2. Diffusion Coefficients from Sorption/Desorption Kinetics. 4.3. Prediction of Diffusion Coefficients. 5: Dissolution Kinetics of Non Aqueous Phase Liquids. 5.1. Aqueous Solubility of Organic Compounds. 5.2. Dissolution Kinetics. 6: Risk Assessment - Remediation. 6.1. Risk Assessment: Release Rates. 6.2. Time Scales of Soil and Groundwater Remediation. 6.3. Transport by Diffusion Compared to Advection. References. Appendices: I. Analytical Methods: TCE and Phenanthrene. II. Methods of Solids Characterization. III. TCE-Diffusion Data: Time-Lag Method. IV. Tracer Diffusion Data. V. Examples for Long-Term Sorption Kinetics of Phenanthrene. Index.

Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics

New modeling paradigms for the sorption of hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments, and rocks

Tracer diffusion coefficients in sedimentary rocks: correlation to porosity and hydraulic conductivity.

Equilibrium sorption isotherms were measured for five different low-polarity organic compounds (benzene, trichloroethene, 1,2- and 1,4-dichlorobenzene, and phenanthrene) over a wide concentration range. The investigated sorbents can be grouped into the following three classes: (1) humic soil organic matter, which shows linear sorption isotherms (solely partitioning, as observed in the peat sample); (2) carbon materials, which were thermally altered (due to their natural history or industrial production) and thus contain a high specific surface area and exhibit nonlinear isotherms, and (3) pure engineered microporous materials (e.g., zeolites and activated carbon), where adsorption is solely due to a pore-filling process. Sorption of all compounds was fitted very well by the Polanyi-Dubinin-Manes (PDM) model, which for sorbents containing humic organic matter (e.g., peat) was combined with linear partitioning. Both the partitioning and the Polanyi-Dubinin-Manes model predict unique sorption isotherms of similar compounds if the solubility-normalized aqueous concentration is used. In addition, an inverse linear relationship between the distribution coefficient (Kd) and water solubility, which was very well confirmed by the data, is obtained. This also leads to unit-equivalent Freundlich sorption isotherms and explains the often observed apparent correlation between sorption capacity at a given concentration (e.g., Freundlich coefficient) and sorption nonlinearity (Freundlich exponent).

Peter Grathwohl

Papers

Influence of organic matter from soils and sediments from various origins on the sorption of some chlorinated aliphatic hydrocarbons: implications on KOC correlations.

Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics

New modeling paradigms for the sorption of hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments, and rocks

Tracer diffusion coefficients in sedimentary rocks: correlation to porosity and hydraulic conductivity.

Solubility-Normalized Combined Adsorption-Partitioning Sorption Isotherms for Organic Pollutants