Showing papers in "Soil Science in 2002"

Near-infrared reflectance spectroscopic analysis of soil c and n

Abstract: Near-infrared reflectance spectroscopy (NIRS) is a rapid and nondestructive analytical technique that can be used to quantify various soil properties. The objective of this study was to evaluate the ability of NIRS to evaluate independently organic C, inorganic C, and total N content of diverse soil

Humification degree of soil humic acids determined by fluorescence spectroscopy

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.

Assessing soil water repellency using the molarity of ethanol droplet (MED) test

Abstract: The molarity of ethanol droplet (MED) test is a popular rapid method for assessing soil water repellency under field and laboratory conditions This paper reviews the theoretical basis of the MED test, discusses con trollable and uncontrollable sources of error affecting its results, and pro poses a detailed protocol for its standardization. Soil water repellency i a function of soil surface chemistry. More specifically, it is a function o the free energy of the solid/gas interface in soil (γ SG ). Because γ SG is no directly measurable in the laboratory, soil water repellency must be as sessed using thermodynamically related parameters such as the initial ad vancing contact angle (θ) or the work of wetting (W W ), The MED tes can be used to determine 0, and in turn W W , but only if some simplifi cations are accepted and the test is performed under standard controller conditions. Wetting theories exclude the dissolution or swelling of the solid by the liquid or chemical reactions between the liquid, solid, and gas phases that change system composition. Consequently, for MED tests to give valid θ estimates, system composition must not change measur ably during 10 s of solid/liquid contact. We discuss system conditions that should be controlled before and during MED testing to improve the validity of test results. Finally, we propose a detailed MED testing pro tocol for possible adoption by commercial analytical laboratories and the soils research community.

CADMIUM UPTAKE BY CROPS ESTIMATED FROM SOIL TOTAL Cd AND pH

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

Clay Dispersion, Infiltration, and Erosion as Influenced by Exchangeable ca and Mg

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

Residence time effects on arsenate surface speciation at the aluminum oxide-water interface

Abstract: Bioavailability of metals/metalloids is often rate limited by contact time (i.e., residence time) in soils and sediments, resulting in irreversible reactions. The fate and transport of the contaminants must be predicted/modeled not only on short-term (<48 h) adsorption/desorption studies but also on long-term (months-years) reactions. However, there is very little information on the long-term effects of metal/metalloid partitioning reactions in soils and soil components. In this study, residence time effects (3 days–1 yr) on As(V) adsorption/desorption reactions and on As(V) surface speciation at the aluminum oxide-water interface were investigated using batch adsorption/desorption experiments coupled with time-resolved Extended X-ray Absorption Fine Structure spectroscopy (EXAFS). Biphasic As(V) adsorption kinetics were observed at pH 4.5 and 7.8, and whereas the reaction at pH 4.5 was nearly completed after 3 days, slow adsorption continued at pH 7.8 after 1 year. The longer the residence time (3 days–1 yr), the greater the decrease in As(V) desorption at both pHs, suggesting nonsingular reactions. EXAFS analyses on aged As(V) reacted aluminum oxide at both pHs showed that As-Al interatomic distances were 3.11 � 3.14 A (� 0.13 A) in all of the aged samples (3 days to 1 yr) at pH 4.5 and 7.8, suggesting that predominantly bidentate binuclear bonding environments were present. As a point of interest, X-ray Absorption Near Edge Structure spectroscopy (XANES) features suggested some changes in the local chemical structure of adsorbed As(V) with aging. The surface transformations such as (i) a rearrangement of surface complexes and/or (ii) a conversion of surface complexes into aluminum arsenate-like precipitates might be important chemical factors responsible for the decrease in As(V) reversibility with aging. (Soil Science 2002;167:303–314)

Sorption of organic phosphorus compounds in Atlantic Coastal Plain soils

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.

ZINC EXTRACTABILITY AS A FUNCTION OF pH IN ORGANIC WASTE-AMENDED SOILS

Abstract: The distribution of various forms of heavy metals after addition to soils needs study to improve predictions of metal solubility, especially when the metal is added to soils with large quantities of organic carbon that oxidize over time. The extractability of added zinc (Zn) was determined in a laboratory study using sequential extractions as a function of pH and organic matter (OM as biosolids) additions to A and B horizon samples of three soils from the Coastal Plain of Maryland. The study used Galestown loamy sand (Psammentic Hapludults), Bertie silt loam (Typic Hapludults), and Othello silt loam (Typic Endoaquults), chosen to represent a typical toposequence in this physiographic province. Watersoluble Zn in the six horizons, with and without biosolids added, decreased with increasing pH from 4.0 to 7.0 and increasing cation exchange capacity (CEC) from 2.2 to 106 mmol c /kg soil. Although this decrease with increasing pH was expected, exchangeable levels of Zn were positively correlated with the CEC only up to pH 5.8 but were negatively correlated at pH > 5.8 in all the soils, suggesting that CEC was not a major contributor to Zn exchangeability at pH > 5.8. The biosolids amendment increased the solubility of Zn in all soils at pH 5.8 in all of the soils. The results indicate that pH was a controlling variable for the redistribution of water-soluble, exchangeable, and nonexchangeable Zn affected by biosolids addition. The higher level of nonexchangeable Zn in the Bertie soil compared with other soils, about 0.80 mmol/kg soil for the biosolids treatments and 0.47 mmol/kg soil for the soils without biosolids at pH 7.0, was attributed to the presence of higher native organic C levels and Fe(III) and Mn(III, IV)(hydr) oxide contents that enhance surface-induced hydrolysis and chemisorption of Zn. The effect of biosolids addition on nonexchangeable Zn retention was more pronounced in B horizons of all the soils, especially at pH > 5.8. The results have implications for predicting the mobility and bioavailability of Zn in soils in which pH and organic C levels are modified purposefully for the disposal of heavy metal and C-rich wastes.

Using field topographic descriptors to estimate soil water retention

Abstract: In field-, watershed-, and regional-scale projects, soil water retention is often estimated from soil textural classes shown in soil maps. The textural classes are relatively broad, often only the dominating textural class is shown, cartographers routinely use error-prone field judgments of soil texture, and soil texture is known to vary along slopes and to depend on the land surface shape. We, therefore, hypothesized that including topographic information in water retention estimation would increase accuracy. To test this hypothesis, we extracted data on 216 soil pedons for soils of moderate and large extent from the Natural Resources Conservation Service (NRCS) soil characterization database. Textural classes, genetic horizon numbers, slopes, position on the slope classes, and land surface shape classes were the field descriptors that we used to estimate water retention at −33 and −1500 kPa potentials for each horizon in each pedon. Because our input variables were both categorical and continuous, regression trees were used for subdividing the samples into the smallest number of the most homogeneous groups, which we tentatively called topotextural groups (TTG). The jackknife cross-validation was used to prune the regression trees to prevent overparameterization. Ten or fewer TTGs were defined for both the −33 and the −1500 kPa retention. The TTGs were different for the two matric potential levels. Using topographic variables and soil horizon seemed to be the most accurate way to make up for errors made in field determination of texture. For the A horizon, the topotextural grouping resulted in estimates that were more accurate than those using laboratory textures only. Although most of the topographic variables in this work are categorical, those variables seemed to be useful for improving estimates of water retention.

Enhancement of uranium phytoaccumulation from contaminated soils

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.

Field evaluation of the new philip-dunne permeameter for measuring saturated hydraulic conductivity

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.

Effect of 25 annual cattle manure applications on soluble and exchangeable cations in soil

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

Influence of the exotic invasive crucifer, Lepidium latifolium, on soil properties and elemental cycling

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

Assessing the Efficacy of Alternative Phosphorus Sorbing Soil Amendments

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

Accumulation of lignin residues in organic matter fractions of lowland rice soils: a pyrolysis-gc-ms study

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

Evaluating aeration criteria by simultaneous measurement of oxygen diffusion rate and soil-water regime

Abstract: Adequate aeration is important for plant root growth. The purpose of this paper was to evaluate aeration criteria by examining the relationships between oxygen diffusion coefficient (ODR) and soil-water potential, soil-water content, air-filled porosity, and gas diffusion rate. In this study we used undisturbed columns and cores of four soils representing different textures (Delhi loamy sand, Arlington sandy loam, Sorrento clay loam, and Imperial silty clay). The ODR was measured under variable soil-water potential conditions. Other aeration parameters, such as oxygen diffusion coefficient (D p ) and air-filled porosity, were calculated based on soil-water content, bulk density, and particle density. Soil-water potential, soil-water content, air-filled porosity, and gas diffusion coefficient at the threshold ODR value of 0.2 μg cm -2 min -1 that provided satisfactory aeration status were evaluated in the four different soils. The threshold ODR value occurred at different soil matric potentials, volumetric water contents, air-filled porosities, and relative gas diffusion coefficients (D p /D o ) for the four test soils, depending on their texture and bulk density. The relationships between ODR and soil-water potential, soil-water content, air-filled porosity, and gas diffusion coefficient were found to be different for the four test soils. All of these results indicate that comparing air-filled porosity and diffusion coefficients at the field capacity for different soils offers little information about the soil aeration capability that influences plant growth directly. We concluded that ODR, a measure that mimics the oxygen supply to root surface, should be used instead for evaluating soil aeration capability.

Estimating Root-Water-Uptake Using An Inverse Method

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.

Macroporosity affects water movement and pore water sampling in peat soils

Abstract: The measurement of chemical concentration profiles in pore water is a starting point for the analysis of biogeochemical processes in waterlogged peat soils. Concentration patterns may be obscured when macroporosity causes preferential flow in column experiments and when pore water is retrieved from the peat by suction. To investigate the magnitude of such effects, we used LiBr as a tracer in peat columns at outflow rates of 0, 2–3, and 8 mm d � 1 . The results were compared with modeled advective-diffusive migration rates. Twenty to fifty percent of the tracer was recovered from depths at which the tracer would have been absent if preferential flow had not occurred. At the high flow rate, the preferential flow was stronger, and the retrieved pore-water was probably in disequilibrium with the matrix. When pore water was retrieved by suction, linear concentration gradients decreased by about 30% through the recovery of water from different depths, and the quality of fitted linear gradients decreased from R 2 � 0.99 to R 2 � 0.82. When flow rates are low (<3 mm d � 1 ) and pore water concentration values from samplers are aggregated or regressed, the obtained concentration profiles seem to represent the vertical distribution of chemical species reasonably well. The use and interpretation of pore water profiles in peat soils is problematic if flow rates are higher and if vertical gradients are based on individual or few data points that have been obtained by suction samplers. (Soil Science 2002;167:98–109)

Sodium-calcium exchange selectivity as influenced by clay minerals and composition

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

The Effects of Tillage on Soil Temperature and Soil Water

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

Measuring Surface Chemical Properties of Soil Using Flow Calorimetry

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)

Effects of wheat residue fertilization on accumulation and biochemical attributes of organic carbon in a central ohio luvisol

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

Soil pore size and geometry as a result of aggregate-size distribution and chemical composition

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.

Andisols on volcanic ash from java island, indonesia: physico-chemical properties and classification

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.

Estimating Variability in Soil Organic Carbon Storage Using the Method of Statistical Differentials

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.

Comparative chemical and spectroscopic characterization of humic acids from sewage sludges and sludge-amended soils

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.

Conversion of Modified Morgan and Mehlich-Iii Soil Tests to Morgan Soil Test Values

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.

Soil boron extractions as indicators of boron content of field-grown crops

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.

Retention and mobility of deltamethrin in soils: 1. adsorption-desorption 1

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.

Phosphate application impacts on cadmium sorption in acidic and calcareous soils

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