Abstract: The humification process increases semiquinone-type free radical concentrations (SFRC) in humus. Their quantification by electron spin resonance spectroscopy (ESR) has been a good indicator of the degree of humification of soil organic matter. As an alternative to relatively complex and expensive ESR spectroscopy, fluorescence spectroscopy was used in this study to evaluate the humification degree of 18 humic acids (HA) extracted from four Brazilian soils under different land use, tillage, or cropping systems. Two fluorescence humification indexes of HA were calculated based on work done by Zsolnay et al. and Kalbitz et al. in 1999, and a third new fluorescence index was proposed. Our proposal is to use the blue wavelength (465 nm) as the HA fluorescence excitation source. As this wavelength is more resonant with the humificated groups present in soil HA samples, our hypothesis is that the resultant fluorescence will provide information about these structures and, therefore, on the degree of humification of the HA. The SFRC varied from 1.90 × 10(17) to 14.75 × 10(17) spins/g HA, characterizing a wide range of the degree of humification of soil HA. The lowest SFRC occurred in native forests (1.90 × 10(17) to 7.50 × 10(17) spins/g HA) and pasture soils (2.30 × 10(17) to 4.64 × 10(17) spins/g HA). In cultivated sites, soil HAs from no-tillage soil were less humified (2.41 × 10(17) to 13.30 × 10(17) spins/g HA) than those in conventionally tilled soil (5.68 to 14.75 × 10(17) spins/g HA). The three fluorescence indexes show the same tendency as SFRC. Our fluorescence method was closely related to procedures found in the works of Zsolnay et al. and Kalbitz et al. (R∼0.9, P < 0.0001) and with SFRC (R∼0.85, P < 0.02), showing their potential as a simple and sensitive technique for evaluating the effect of land use and soil management systems on the humification degree of soil humic acids.

Abstract: Although it is well established that Cd uptake by crops is dependent on soil total Cd and soil pH, actual prediction of uptake based simultaneously on these two soil parameters has not generally been tested. In the present study, reanalyzing available data on the uptake of cadmium by lettuce, Swiss

Abstract: Soils of the US Corn Belt often experience surface sealing, low infiltration, and erosion under rainfall, all of which result in economic loss. This study seeks to establish if high Mg content in these soils can have an adverse effect on soil structure, clay dispersability, water intake rate, and er

Abstract: Organic phosphorus (P) can comprise a significant amount of the total P in animal wastes, yet there is little information on the potential for organic P to be transferred from soils to watercourses. We examined the adsorption of organic P compounds to soils typical of the southeastern United States, i.e., Blanton Sand (loamy, siliceous, thermic, Grossarenic Paleudult), Cecil sandy clay loam (fine, kaolinitic, thermic, Typic Kanhapludult), and a Belhaven sandy loam (loamy, mixed, dysic, thermic, Terric Medisaprist). The behavior of four organic P compounds was studied: adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP), and inositol hexaphosphate (IHP); while KH2PO4 (ortho-P) was used as an inorganic reference. Laboratory studies were conducted to determine the effects of concentration (0-130 p.g P mL-1 ), pH (4.6-7.6), and soil properties on P adsorption. All the organic P compounds had greater adsorption than KH 2PO4 on the Blanton and Cecil soils at all concentrations and ranges of pH. In the Belhaven soil, IHP had the greatest sorption followed by KH 2PO4 and the nucleotides (ATP, ADP, and AMP, respectively). Adsorption of organic P was positively correlated with soil organic matter and Fe and Al contents. The greater sorption of some organic P compounds over that of ortho-P suggests that these compounds may pose less of a threat to water quality, although this preferential sorption may increase soluble P in situations where there is displacement of ortho-P by organic P added in manures.

Abstract: Cattle manure contains a high level of soluble salts, and its application to agricultural land may alter soil properties and affect crop production. The purpose of this study, conducted in Fall 1998, was to evaluate the effect of 25 annual cattle manure applications on solution and exchangeable cati

Abstract: One of the most sensitive parameters in hydrological models, the saturated hydraulic conductivity (K s ), is also one of the most problematic measurements at field scale in regard to variability and uncertainty. The performance of a new type of simple and inexpensive field permeameter, the Philip-Dunne permeameter (PD), is compared with two established alternatives, the laboratory constant head permeameter (LP) and the field Guelph permeameter (GP). A PD prototype, a protocol of usage, and a numerical routine to find K s were developed and tested on a 70-point array laid out on an 850-m 2 volcanic soil plot. A power transformation was applied to the raw data using the three methods, and the transformed data were shown to be normally distributed. The LP and GP data were better described by a log-normal distribution, whereas the PD data could also be approximated with a power-normal distribution. A factor of 3 was found to relate PD, LP, and GP hydraulic conductivity estimates, E[Ks], such that E[K s -PD] ≅ 3 E[K s -LP]; E[K s -LP] ≅ 3 E[K s -GP]. Such differences may be explained by the different water infiltration geometries and sample wetted volume for the three methods. The PD has advantages over the other two methods in terms of personnel involved, preparation time, and ease of operation. Additionally, the PD methodology required a smaller number of samples (41% less than GP and 69% less than LP) to estimate the population mean K s . Both PD and GP also give the suction at the wetting front, an important parameter that characterizes the unsaturated flow properties of the soil.

Abstract: Chelation and complexation of uranium (U) and soil acidification were evaluated as practical ways to solubilize, detoxify, and enhance U accumulation by plants. Sunflower (Helianthus annuus) and Indian mustard (Brassica juncea) were selected as potential U accumulators for U phytoextraction in one U mine tailing soil (469 mg U kg -1 ) and nine acid and calcareous soils (pH 4.7 to 8.1) contaminated with different rates (100 to 600 mg U(VI)kg -1 ) of uranyl nitrate (UO 2 (NO 3 ) 2 .6H 2 O). To enhance U phytoextraction, organic chelates were added to soils alone or as complexed-U forms of CDTA, DTPA, EDTA, and HEDTA, and citric and oxalic acids at rates of 1 to 25 mmol kg -1 , to soils with 4-week old seedlings. Dry matter production, U concentration in shoots and roots, and soil pH were measured. Contaminated soils were also evaluated for U desorption and by fractionation. Uranium desorption was performed with 2 to 20 mmol kg -1 of citric acid, CDTA, DTPA, and HEDTA. Uranium fractions [(exchangeable, carbonate, manganese (Mn), iron (Fe), organic, and residual)] were determined after 4 weeks of incubation. Plant dry matter production and U accumulation varied with soil contamination rate, chelate, organic acid form and rate, and soil type. The highest U concentration was in plants growing in calcareous soils and the lowest in clayey acid soils with high Fe and Mn oxides and organic matter content. Addition of citric and oxalic acids increased U accumulation and U translocation to the shoots significantly. Addition of 20 mmol of citric acid kg -1 to loamy acid soils reduced the soil pH to below 5.0 and increased U concentration in shoots to 1400 mg U kg -1 or by 150-fold, but addition of complexed-U forms had little effect on U translocation to shoots. Citric acid was the most effective chelate in desorption and plant accumulation of U. Uranium phytoacumulation was limited to acid soils with low adsorptive potential and to alkaline soils with carbonate minerals.

Abstract: Plant species and plant communities can alter element cycling promoting divergent pathways of soil development. We hypothesized that the exotic invasive crucifer, Lepidium latifolium, altered biogeochemical cycling relative to pre-existing vegetation such that sodium-affected subsoils are ameliorate

Abstract: Concern over the contribution of agricultural phosphorus (P) to fresh water eutrophication has focused attention on practices that decrease P losses from agricultural soils. At present, there are few management options for soils with P levels in excess of crop P requirements other than restricting P

Abstract: In tropical Asia, multiple annual cropping of lowland rice and the associated submerged soil conditions have been linked to long-term changes in nitrogen (N) cycling and the chemical nature of soil organic matter. To identify changes in organic matter properties, two humic acid fractions and whole s

Abstract: It is extremely challenging, if not impossible, to measure distribution of root-water-uptake or root density directly, either in the laboratory or in the field. To estimate root-water-uptake distribution in soils, the authors of this paper developed an inverse method, whereby measured values of water content in soil profiles with root-water-uptake were used as input information, which can be acquired relatively easily and accurately. Then a soil water flow equation incorporating an unknown sink term was solved inversely for the sink term, which characterizes the root-water-uptake distribution in the root zone. The estimated distribution of root-water-uptake rate was used to calculate the normalized distribution of relative root density, from which the root-water-uptake model was established. Based on the model, soil water flow with root-water-uptake was simulated successfully. Examples of numerical experiments were designed to examine the accuracy and stability of the proposed approach for estimating the average root-water-uptake rate, considering different time intervals between successive measurements of the input distributions of soil water content, spatial intervals of the measurement points along the soil profile, simulating depth, different soils, variation of the saturated hydraulic conductivity, and the stochastic nature of the measured soil water content. Examples were also used to demonstrate applications of the method. The results showed that the inverse method is reliable for estimation of distribution of the root-water-uptake rate, compared with the theoretical values. The proposed method is useful for estimation of the normalized distribution of the relative root density, from which the root-water-uptake model can be determined and the soil water flow with root-water-uptake can be simulated continuously.

Abstract: Knowledge of exchangeable cation chemistry can provide clues about tendencies toward either soil dispersion or flocculation as exchangeable sodium accumulates. The accumulation of sodium might be influenced by soil texture and degree of salinity. The effects of clay minerals, composition, and salini

Abstract: The potential of crop residue fertilization as a carbon sequestration technology was evaluated in a central Ohio Luvisol (fine, mixed, mesic Aeric Ochraqualf). Wheat (Triticum aestivum L.) straw was applied at three rates (bare: 0; low: 8 Mg; and high: 16 Mg ha−1 yr−1) without (−F) and with (+F) add

Abstract: Tillage in farmland plays an important role not only as a soil management tool for improving the plant root environment, but also as a factor that impacts the hydrological cycle and the energy balance in a region. This is because tillage affects soil moisture and soil temperature greatly in the unsa

Abstract: Soil pore size and pore geometry are important properties affecting soil hydraulic properties. Using scanning electron micrographs and image analysis, we quantified the actual pore-size distribution and pore shape in undisturbed soil cores. Aggregate-size distribution was also quantified for the same micrographs. For soils with similar texture, we observed a decrease both in the median aggregate size and in the aggregate-size distribution when the sodium content in the soil increased. We hypothesize that the decrease in the aggregate stability is caused by the weakening of the binding capacity of the cementing agents bonding the domains that form the aggregates. An equivalent decrease in the pore-size distribution was found with increasing sodium and pH. There was a significant correlation between median aggregate size and median pore size, but there was not a significant correlation between median pore diameter and soil texture.

Abstract: Java Island in Indonesia is dominated by volcanic ash soils. A study was conducted to characterize the soil's physico-chemical properties in order to assess the influence of change of parent material on differing soil characteristics along an E-W sequence. All of the soils are Andisols of varying chemical composition. Soil pH and exchangeable Ca decreased from East to West Java, attributable to the parent ash becoming more acid from east to west. However, the Si, Al, and Fe extracted by acid-oxalate and the estimated amounts of allophane (11-35%) and ferrihydrite in the fine earth increased from east to west, showing that development of active forms of Al and Fe is favored by strongly leaching environments. This trend holds true for the point of zero net charge (PZNC) and for pH o . Samples rich in allophane showed relatively high PZNC. The relatively high pH o values for the Central and West Java soils indicate development of net positive variable charges at pH < pH o . East Java and Kopeng soils are capable of holding more basic cations than the other soils at the actual soil pH. Therefore, these soils are less likely to be deficient in Ca and Mg under yearly application of acidifying nitrogenous fertilizers.

Abstract: Flow calorimetry, which is ideally suited for measuring reactions oc­ curring at the liquid/solid interface, has been used to study the surface chemistry of many types of solids, but little use of it has been made in the study of surface reactions of soils. The purpose of this study was to demonstrate the application of flow calorimetry to the study of two fun­ damental soil chemical processes, namely cation exchange and phosphate sorption. Surface horizon samples of a Typic Acrorthox and a Typic Tropohumult from Puerto Rico, a strong acid cation exchange resin (Dowex 50W-8), and an amorphous Al(OH) 3 were used. Heats for K/Ca exchange on the Dowex resin and the Oxisol, and K/Na exchange on the Ultisol, were consistent with literature values that were obtained using conventional batch calorimetry or derived from the temperature depen­ dence of the exchange constant. Although peak areas associated with a given pair of exchange reactions were equal, peak shapes were generally not equivalent, indicating differences in the rate at which the two reac­ tions occurred. For example, Ca displacing exchangeable K occurred more rapidly than the reverse reaction on the Dowex resin. The reaction of phosphate with the Ultisol and amorphous Al(OH) 3 was exothermic. Exposure of the soil to several cycles of phosphate was sufficient to sat­ urate the sorption sites, as evidenced by the loss of a detectable heat sig­ nal. However, phosphate reactive sites were regenerated by flushing the column with a salt solution at pH 10. Precipitation of Al-phosphate was shown to be endothermic, confirming that precipitation was not the pri­ mary mechanism for phosphate sorption in this study. The results of this study show that flow calorimetry can provide valuable information about surface chemical reactions in soils that cannot be obtained readily by other methods. (Soil Science 2002;167:782–790)

Abstract: The diverse nature of soils introduces uncertainty into the estimation of soil organic carbon (SOC) storage. Laboratory analyses indicate C concentration in soils, but the soil layer thickness, bulk density, and percent of fragments > 2 mm must be known in order to estimate SOC storage. Ideally, measurements of SOC concentration are performed on the same soil samples used to determine bulk density and percent of fragments > 2 mm, but this is frequently not possible. Often measurements of SOC concentration, bulk density, and percent of fragments > 2 mm are obtained separately from the same soil layer, which causes propagation of error when estimating SOC storage. Furthermore, measurements of bulk density and percent of fragments > 2 mm are more difficult to obtain than measurements of SOC concentration. Because of this, samples of bulk density and percent of fragments > 2 mm are often taken independently and less frequently than samples for SOC concentration. The objective of this study was to derive an estimation method for the variability in SOC storage estimates as a function of SOC concentration, bulk density, percent of fragments > 2 mm, and soil thickness. The method of statistical differentials, also known as the delta method, was used to obtain an estimate of the variability in SOC storage estimates. The variance estimation procedure is illustrated using previously published data for the Russian Chernozem under different management regimes. The method of statistical differentials is a valuable tool for obtaining variance estimates in a large class of problems with similar characteristics.

Abstract: The main objectives of the present work were to evaluate the compositional and functional differences between a sewage sludge humic acid (HA) and nonamended soil HA and to determine the effects of various sewage sludge amendments on the composition, structure, and chemical properties of HAs from uncultivated and cultivated soils. For this purpose, the HA fraction was isolated by conventional methods from a sewage sludge used as soil amendment, the nonamended soil, and soils amended with two rates of dewatered and liquid sludges, either in the presence or absence of barley. The HAs isolated were characterized comparatively for their compositional, structural, and chemical properties by use of elemental analysis and by Fourier Transform infrared (FT IR), fluorescence, and electron spin resonance spectroscopies. The sludge HA was predominantly aliphatic and, therefore, markedly different from the nonamended soil HA and was characterized by a low oxygenated functional group content, high contents of S- and N-containing groups and polysaccharide components, very low free radical concentration, high molecular heterogeneity, low ring polycondensation and polymerization, and low humification degree. The application of the dewatered sludge induced only limited modifications in the structural and chemical properties of HAs from amended soils, which were only partially affected by the amendment rate used. However, marked modifications of HAs did occur in soils amended with liquid sludge, especially at high rates. The absence or presence of barley cultivation did not show any measurable effect on the composition and properties of sludge-amended soil HAs.

Abstract: In several states in the Northeastern U.S., the Morgan or Modified Morgan soil tests are used as the basis for both fertilizer recommendations and P runoff risk indices. However, private laboratories servicing these states typically use the Mehlich-III solution as their basic soil test extractant. To meet Natural Resources Conservation Service standards for nutrient management and to use land grant university research databases to derive recommendations, accurate conversions from Mehlich-III and Modified Morgan to Morgan are needed. A study was conducted in New York to: (i) develop models that convert Mehlich-III P, K, Ca, and Mg soil tests to Morgan equivalents; and (ii) evaluate the impact of the use of these prediction models on agronomic recommendations for corn and the New York P index. Soils from 235 locations (27 different New York soil types) were analyzed for pH, modified Morgan P, and Morgan- and Mehlich-III extractable P, K, Ca, Mg, Fe and Al. Multiple regression analysis was used to derive conversion models that fit the data. The models were validated, and the impact of their use on fertilizer recommendations was assessed using a set of >10,000 independently collected New York soil samples. Morgan and Mehlich-III extractable K, Ca, and Mg were correlated linearly with slopes approaching 1. For P, the best model fit was obtained using pH, Mehlich-III P, Ca, and Al as independent variables (r 2 = 0.88). A slightly less reliable prediction was obtained without Al (r 2 = 0.82). The use of Morgan equivalents did not alter the percentage of low, medium, high, and very high soils in the New York data set, nor did it affect the P index classification. Recommendations for corn derived from a database with independently collected Mehlich-III soil test data (without Al) were identical to those obtained using measured Morgan values for 57% of all samples. An additional 32% showed 20 P 2 O 5 ha -1 . Inclusion of Mehlich-III Al data is expected to improve the accuracy of the recommendations and assessment of the P index. We conclude that conversion equations can be used to derive accurate Morgan equivalents based on pH, Mehlich-III P, Ca, and Al, but the results need to be verified based on land use history.

Abstract: Determining the relationship between soil B and crop B content can help predict when crops will respond to B fertilizer and when B toxicity may be expected. Such a relationship can then be used to make fertilizer recommendations or to flag conditions of potential B toxicity. Soil samples were obtained from 65 sites located in the Broadview Water District in the San Joaquin Valley of California. A diverse set of extractants was evaluated including: hot water-soluble, 1:1 soil:distilled water and 1:2 soil:distilled water, ammonium acetate, calcium chloride-mannitol, and DTPA-sorbitol extracts. Soil extract B values were correlated significantly with various B reactive soil constituents, including aluminum and iron oxide, clay, organic matter, and calcium carbonate content. The 1:1 water extract B was highly significantly correlated (99% level) with other measures of extractable B used in the study. Extractants were compared on soil samples collected from six depths at 65 field sites in the San Joaquin Valley of California that were cropped to alfalfa, melons, and cotton. Boron concentrations of whole plants and composites of 10 leaves were determined. Plant sampling occurred at the time of soil sampling for the alfalfa. Cotton and melons were sampled at flowering and prior to fruit set, the recommended growth stages, respectively, for tissue sampling, and 6 weeks thereafter. Five weeks later the cotton was sampled a third time. Significant correlations (95% level) between extractable soil B and plant B were found for melons and cotton but not for alfalfa. Correlation coefficients for the ammonium acetate, DTPA-sorbitol, and 1:1 water extract were not statistically significantly different (95% level). Although significant correlations (95% level) were obtained, the equations provided relatively poor predictive capability. These results illustrate the difficulty of predicting plant B content based on soil B analyses from a single soil sampling.

Abstract: Pesticide adsorption and desorption are important processes that influence the amount of pesticide retained by the soil matrix and its susceptibility to movement in the soil profile. In this study the adsorption-desorption behavior of the insecticide deltamethrin was investigated in soils with different physical and chemical properties. Four soils having different organic matter content, clay content, and pH were used along with acid-washed sand (reference material). An adsorption kinetic batch method was used for a wide range of deltamethrin concentrations and reaction times. Desorption was carried out following 360 h of adsorption using successive dilutions with 0.005 M CaCl 2 background solution. This was followed by an extraction step using methanol. Based on the distribution coefficients (K d ) that were derived from adsorption isotherms, deltamethrin exhibited strong retention over time but varied extensively among soils. The K d values after 1-day sorption ranged from 13 to 98 mL/g soil. With the exception of the reference sand material, adsorption was not kinetic. Deltamethrin adsorption was correlated positively with increasing cation exchange capacity and decreasing soil pH. Strong deltamethrin hysteresis was observed for all soils as depicted by discrepancies of adsorption from desorption isotherms. The extent of recovery or release of applied deltamethrin varied among soils and input concentrations, but it did not exceed 10.2% of the total amount adsorbed. Moreover, for all soils the total amount of deltamethrin retained following desorption ranged from 78 to 97% of total input. The only exception was for a nonacidic Vacherie soil (pH of 7.6), which showed the highest recovery with the lowest amount retained (39.5% of input). Low retention may be caused by solubilization of dissolved carbon. As a result of observed strong low recovery, we conclude that deltamethrin is not susceptible to leaching losses from the zone of application.

Abstract: The biodegradative capabilities of ten rhizobial species and four field isolates were evaluated in this study using growth studies, dense suspension cultures, and soil studies. After a preliminary screening, selected species were chosen for their degradative effect on aromatic, halogenated aromatic, and aliphatic substrates. The substrates utilized were: benzoate, phenol, 2-hydroxybenzoate, 3-hydroxybenzoate, 4-hydroxybenzoate, catechol, resorcinol, 2,3-dihydroxybenzoate, 2,4-dihydroxybenzoate, 2,6-dihydroxybenzoate, 3,4-dihydroxybenzoate, phenoxyacetate, 2,4-dichlorophenoxyacetate, cresols, mandelates, phthalate, 2-bromobenzoate, 2-chlorobenzoate, 4-chlorobenzoate, 2,4-dichlorobenzoate, 2-chlorophenoxyacetate, 4-chlorophenoxyacetate, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, and hexadecane. Sinorhizobium xinjiangensis, Rhizobium leguminosarum, R. leguminosarum biovar trifolii, Bradyrhizobium japonicum, and strain V2 (field isolate) were able to metabolize a variety of organic compounds such as hydroxy- and dihydroxybenzoates, halogenated aromatic compounds, and alkanes. Significant differences were observed among the strains showing interspecies variability in their response to the different compounds. Dense cell suspension experiments conducted evaluating substrate loss, 4-chlorophenol, 4-chlorobenzoate, 4-chlorophenoxyacetate, cresols, resorcinol, and mandelate, among others, were metabolized although they did not support growth. Soil studies were performed showing that the addition of rhizobial inocula increased degradation of hexadecane in a soil environment.

Abstract: Experimental methods are needed to measure infiltrations at several locations simultaneously during rainfall or irrigation. The objective of this study was to test the feasibility of using a time domain reflectometry (TDR) probe installed vertically into the soil to track the propagation of the wetting front during infiltration. We used a numerical method to simulate wave traces. The dielectric constant above the wetting front and the probe characteristics were known. The trace simulation method was coupled to a nonlinear optimization program to fit the apparent lengths of the TDR probe above and below the wetting front and the dielectric constant of the soil below the wetting front. The optimization program employed a genetic algorithm. The progression of the wetting front into the soil was recorded as a function of the apparent length of the section of the TDR probe above the wetting front. Direct measurements of the wetting front advance were obtained from observations of infiltration in a clear acrylic cylinder packed with soil and ponded with water. The root mean square errors of the predicted wetting front depths did not exceed 0.4 cm. The method shows promise in estimating wetting front depth as a function of time.

Abstract: Land treatment of sewage sludge and the use of chemical fertilizers have resulted in cadmium (Cd) contamination of some soils. The effect of a soil’s ionic environment on the availability of heavy metals in soils and plants is of concern. In this study, we investigated the environmental availability

Abstract: Studies on soil organic matter (SOM) cycling in different climate zones are an important basis for further understanding of the feedback mechanism of terrestrial carbon storage to global climatic changes and are crucial for accurate projections of future concentrations of CO 2 in the atmosphere. Using thin-layer methods, six soil profiles in the Dinghushan Biosphere Reserve (DHSBR), South China, and the Xiaoliang Ecological Station of the South China Institute of Botany, Chinese Academy of Sciences (CAS) were excavated and sampled for studies on the dynamics of SOM in the southern subtropical areas, based on SOM δ 13 C, Δ 14 C, soil grain size characteristics, and soil organic carbon (SOC) contents. Results indicate that the turnover of SOM occurs in three stages: (i) Rapid turnover of SOM occurs within 100 years, with SOC content decreasing sharply downwards from the ground surface and δ 13 C values becoming correspondingly enriched in 13 C as a result of carbon isotope fractionation in the process of SOM turnover; maximum till is reached at about 260-270 years; (ii) from about 260-270 years to 800-1400 years, SOM turnover rates lessen, SOC content decreases slowly downwards, and δ 13 C values become gradually depleted in 13 C due to the decomposition of SOM compartments with higher δ 13 C values; (iii) after about 1500 years, SOC content approaches the minimum, with slight fluctuations, and δ 13 C values become stable. Comparison analyses suggest that soil clay materials control existing forms and turnover processes of SOM directly, SOM in the soil sections with high clay content at DHSBR are not easily decomposed and have longer turnover periods, and soil textures are an important factor controlling SOM dynamics. Fall leaf litter generally has more negative δ 13 C value than the topsoil samples, which may be a result of isotope fractionation caused by rapid carbon decay prior to the penetration of carbon from the litter into the topsoils. Above-ground vegetation species and composition impact SOM turnover processes directly; δ 13 C analysis may be an important tool for determination of the improvement in soil quality during the restoration of degraded ecosystems. Vegetation occupation history also influences the SOM dynamics of soil profiles at different sites in one area with similar vegetation species, as shown by the soil profiles at the Xiaoliang Ecological Station of the South China Institute of Botany, CAS.

Abstract: Addition of polysaccharides to soils or their formation in situ through microbial activity increases the stability of soil aggregates. Like other components of soil organic matter, polysaccharides are expected to affect strongly the flocculation and dispersion behavior of clays, which are the most important soil component. The influence of polysaccharide concentration, molecule characteristics, and pH, on flocculation and rheological properties of Na-montmorillonite were studied. Flocculation values (FV) increased with increasing concentrations of the anionic polysaccharide polygalacturonic acid (PGA). The pattern was similar at pH 4 and 8: a relatively sharp increase in FV with small additions of PGA up to a concentration of 10 mg L -1 (136.0 and 160 mmol L -1 ) and a slight to moderate increase thereafter. At pH 6 a different pattern was observed. The FV changes at the lower PGA concentrations (up to 10 mg L -1 ) were similar to those observed for pH 4. At higher concentrations, a further sharp increase in the FV was found. Addition of 1 mg L -1 PGA at pH 10 resulted in a FV increase to 37.0 mmol L -1 . For higher PGA concentrations, the FV remained basically unchanged. Results obtained by measurements of the rheological properties of suspensions to which PGA was added provided additional proof for the clay-PGA interaction and followed similar trends. The Na-montmorillonite suspension exhibited non-Newtonian flow properties. When PGA was added to the Na-montmorillonite suspension, the flow behavior gradually changed from non-Newtonian to Newtonian as the PGA concentration increased. The mechanisms proposed to explain the interactions between Na-montmorillonite and the anionic polysaccharide (PGA) are (i) edge charge reversal and (ii) mutual flocculation (heteroflocculation). These mechanisms are similar to those proposed previously for suspensions of Na-montmorillonite to which humic substances (HS) were added. The dissimilarities are, apparently, a result of the differences between structure and characteristics of the molecules of these organic materials. Additions of noncharged polysaccharides (dextrans) resulted in completely different responses. Additions of the low molecular weight dextran (T-40, MW 40000) did not result in significant changes in the FVs of Na-montmorillonite. In contrast, two neutral polysaccharides tested (T-500, MW 500,000 and T-2000, 2,000,000) enhanced clay flocculation and consequently caused a sharp decrease in the FV.

Abstract: Although Cr(III) is considered a Cr species with low mobility and toxicity, the potential oxidation of Cr(III) to Cr(VI) in soils containing Mn requires further scientific attention because of the acute toxicity of Cr(VI). This study evaluates the inhibition or enhancement of Cr(III) oxidation by Mn oxide in the presence of various organic ligands and concentrations. Batch experiments indicate that 200 μM of organic ligands inhibited 20 μM Cr(III) oxidation by Mn oxide at pH 4 because of the occurrence of reductive dissolution of Mn oxide. Although oxalate did not show strong inhibition of Cr(III) oxidation at pH 10, nevertheless, citrate and N-hydroxyethyl-ethylenediamine-triacetic acid (HEDTA) ligands did retard Cr(III) oxidation. It is possible that the co-precipitation of Cr(III) and organic ligand, which has a low dissociation constant, results in low release of Cr(III) and subsequent oxidation. The current results imply that the management of Cr(III)-containing waste is very important to prevent potential oxidation of Cr(III) by Mn oxides, particularly at low pH. However, the presence of organic ligands in the field may lead to low Cr(III) oxidation where Cr(III) waste is disposed.

Abstract: Information regarding the mobility of applied chemicals to soils is essential for environmental assessment of potential leaching to groundwater supplies. In this study, the mobility of deltamethrin applied to soil columns with different properties was investigated. The approach used was that of a mo