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Showing papers in "Soil Science in 1989"


Journal ArticleDOI
TL;DR: In this paper, the authors sampled the soil horizons of 40 important Belgian soil series, with textures ranging from sand to heavy clay, and measured their moisture retention characteristic (MRC).
Abstract: We sampled the soil horizons of 40 important Belgian soil series, with textures ranging from sand to heavy clay, and measured their moisture retention characteristic (MRC). Of these horizons, the particle-size distribution in nine fractions, the dry bulk density, and the carbon content were determin

709 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the retention of 15 elements by 11 soils from 10 soil orders to determine the effects of element and soil properties on the magnitude of the Freundlich parameters Kd and n.
Abstract: We studied the retention of 15 elements by 11 soils from 10 soil orders to determine the effects of element and soil properties on the magnitude of the Freundlich parameters Kd and n. The magnitude of Kd and n was related to both soil and element properties. Strongly retained elements, such as Cu, H

265 citations


Journal ArticleDOI
TL;DR: A physically-based theory to explain finger persistence was presented in this article, where it was shown that fingers persist over long periods of constant infiltration and in subsequent infiltration cycles. But, it was not shown that gravity-driven fingering can occur during vertical infiltration.
Abstract: Wetting-front instability, or gravity-driven fingering, can occur during vertical infiltration. Previous studies found that fingers persist over long periods of constant infiltration and in subsequent infiltration cycles. We present a physically based theory to explain finger persistence. The theory

254 citations


Journal ArticleDOI
TL;DR: The use of spatial distribution of effective porosity (Φe) to estimate the distribution of saturated hydraulic conductivity (K2) was evaluated on five new soils and on a combination of soils as discussed by the authors.
Abstract: The use of spatial distribution of effective porosity (Φe) to estimate the distribution of saturated hydraulic conductivity (K2) is evaluated on five new soils and on a combination of soils. The K2 is related to Φe by a generalized Kozeny-Carman equation. This equation is then combined with scaling

209 citations


Journal ArticleDOI

150 citations


Journal ArticleDOI
TL;DR: In this paper, the authors determined the spatial sensitivity of a TDR measurement and the distribution of the sensitivity within a volume of soil using the time-domain reflectometry (TDR) method.
Abstract: With any method for measuring soil water content it is useful to know the spatial sensitivity of the measurement, i.e., what volume of soil is measured and what the distribution of sensitivity is within that volume. We determined this information for the method of time-domain reflectometry (TDR), us

132 citations


Journal ArticleDOI
TL;DR: In this article, forest soil on a 23-ha watershed in New Hampshire was sampled quantitatively by excavating 60 0.5m2 pits by horizon in the forest floor and depth strata in the mineral soil.
Abstract: Forest soil on a 23-ha watershed in New Hampshire was sampled quantitatively by excavating 60 0.5-m2 pits by horizon in the forest floor and depth strata in the mineral soil. Carbon (C), organic matter (OM), and bulk density (BD) were measured to determine relationships among these properties by soi

131 citations


Journal ArticleDOI

100 citations


Journal ArticleDOI
TL;DR: In this paper, the unimodal lognormal distribution can describe PSD, to within chosen degrees of approximation, over only about half of the USDA triangle, where eligible textures are excluded primarily by their width of textural spread.
Abstract: The assumption that particle-size distribution (PSD) in Mil may often be described as approximately lognormal was tested and found to be inadequate for many textures. With texture specified by mass fractions of clay, silt, and sand in a texture triangle, it is shown that the unimodal lognormal distribution can describe PSD, to within chosen degrees of approximation, over only about half of the USDA triangle. “Disallowed” textures are excluded primarily by their width of textural spread, requiring excessive undersize (d < 0.02 μm) or oversize (d > 2 mm) tails in the distribution. They would require alternative distribution functions (e.g., skewed unimodal, bimodal). Equations are given for the two lognormal (size “mean” and “spread”) parameters for eligible textures within the “allowed” triangle area. The theory enables mapping between triangles of different texture systems (e.g., USDA, International) for eligible textures. The rationale of predicting soil properties from two-parameter textural representations is discussed. Two. classes of property are identified, according to their likely optimal regression parameters: (1) properties dominated by the clay or colloidal fraction (mass-fraction parameters, only two of which are independent) and (2) properties dependent on overall particle- or poresize distributions (transformed, size-distribution parameters). The lognormal parameters derived here offer a new basis for regression of class 2 properties for eligible textures.

96 citations


Journal ArticleDOI
TL;DR: In this article, the main and interactive effects of humic acids and anionic (AS) and nonionic (NS) surfactants on aggregate stability of two soils: a fragile, sandy loam, Typic Psammaqnent and a strong, clay, Vertic Xerochrept, were evaluated.
Abstract: We used two sets of experiments to evaluate the main and interactive effects of humic acids (HA) and anionic (AS) and nonionic (NS) surfactants on aggregate stability of two soils: a fragile, sandy loam, Typic Psammaqnent and a strong, clay, Vertic Xerochrept. For the main effects, the soils were treated at six rates, 0, 10, 50, 100, 1000, and 10000 mg/kg, with either HA, AS, or NS. A 3 x 4 factorial design, comprising three HA rates (0, 50, and 1000 mg/kg) and four AS or NS rates (0, 10, 100, and 1000 mg/kg), was used to assess the interactive effects. Changes in aggregate stability were measured at both the macro- and micro- levels by wet-sieving and clay dispersion techniques, respectively. On both soils, the percentage of water-stable aggregates increased with increasing rates of HA and NS, whereas aggregate stability was reduced progressively with increasing concentration of AS. The HA was, however, relatively more effective on the more fragile soil, whereas the converse was true for the NS. At higher NS application rates (100 mg/kg), clay dispersion decreased on the clay but increased slightly on the sandy loam soil, indicating, respectively, increased and decreased microaggregate stability. The HA and AS, however, increased clay dispersion on both soils at higher rates. The interaction of HA with NS was positively synergistic in increasing the stability of aggregates at macro- and micro- levels in both soils. The HA-AS interaction, however, reduced the stability of the sandy loam, but increased that of the clay soil at both levels of aggregation. The possible modes of action of these additives and the management implications of their effects on soil structure are emphasized.

80 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the contribution of organic matter to the cation exchange capacity and the specific surface area (SSA) of organomineral complexes in soils, and studied a horizons of four soils (two Hapludalfs and two Argiudolls) in central Iowa.
Abstract: To investigate the contribution of organic matter to the cation exchange capacity (CEC) and the specific surface area (SSA) of organomineral complexes in soils, we studied A horizons of four soils (two Hapludalfs and two Argiudolls) in central Iowa. The effect of mineralogy on CEC and SSA was held n

Journal ArticleDOI
TL;DR: In this paper, the authors used the Langmuir isotherm to determine the phosphate sorption of 16 important soil series developed over major parent materials in the different ecological zones of Ghana.
Abstract: Using the Langmuir isotherm, we determined the phosphate sorption of 16 important soil series developed over major parent materials in the different ecological zones of Ghana. The phosphate sorption maximum was highest (222 to 286 ppm, mean 254) in forest soils and in one Vertisol, followed by the forest/savanna intergrade (112 to 147 ppm, mean 133), and was lowest (39 to 93 ppm, mean 69) in savanna soils. With the exception of two soil series, Akuse and Volta, all the soils had low standard P requirements (i.e., the amounts of P required to attain 0.2 ppm P in equilibrium solution). The standard P requirement followed the same trend as and was significantly correlated with sorption maximum (r = 0.854). The influence of parent material and pH, organic matter, clay, free Fe2O3, and Al2O3 content on the sorption maximum was studied by linear, partial, and multiple-regression analysis. The phosphate sorption maximum was highly significantly correlated with soil properties in the order: free Al2O3 (X5; r = 0.912), clay content (X3; r = 0.894), free Fe2O3 (X4; r = 0.830), and organic carbon (X2; r = 0.790); the relationship with soil pH (X1 per se did not attain significance. This relative importance of the effects of soil properties of P sorption was confirmed by partial regression analysis. Generally, combining two or more soil properties in a multiple-regression equation improved the prediction of the sorption maximum. However, the best prediction of P sorption could be made using the multiple-regression equation Y = 13.40 + 30.83X2 + 4.04X3 + 0.003X4 + 0.18X5 (R = 0.984) and by the more easily and frequently determined soil properties: organic carbon and clay, Y = 13.93 + 56.65X2 + 6.61X3 (R = 0.935).

Journal ArticleDOI
TL;DR: In this paper, a procedure consisting of calculating cracking and subsidence with the computer model FLOCR, using 30-yr weather data was applied to quantify the influence of installing tile drains in a poorly drained heavy clay soil on swelling and shrinkage.
Abstract: Numerous methods have been developed to estimate potential swelling and shrinkage of soils. In practice, however, one is usually interested in the actual magnitude of these processes. This paper describes a procedures developed to predict actual swelling and shrinkage in clay soils. The procedure consists of calculating cracking and subsidence with the computer model FLOCR, using 30-yr weather data. The procedure was applied to quantify the influence of installing tile drains in a poorly drained heavy clay soil on swelling and shrinkage. It appeared that both magnitude and frequency of swelling and shrinkage of the soil matrix would strongly increase, especially in the subsoil. Consequently, buildings, pavements, and other constructions on this clay soil have an increased risk of damage. Agricultural users of the soil will profit from a water regime that is more adapted to their needs and, in the long run, also from an improvement in the soil structure.

Journal ArticleDOI
TL;DR: In this article, the Industrial Revolution and Land Transformation Practices Leading to Land Transformation practices leading to land transformation practices are described and compared. And the authors present a set of criteria for observing and measuring changes associated with land transformation.
Abstract: Introduction to Land Transformation and Agriculture Agricultural Land Use in Space and Time Transformation of the Land in Pre-Industrial Time The Industrial Revolution and Land Transformation Practices Leading to Land Transformation Impact of Irrigation on Land Transformation Impact of Mechanization on Land Transformation Impact of Land Surface Modification and Conservation Practices on Land Transformation Impact of Wetland Reclamation on Land Transformation Use of Fertilizers and Soil Amendments Plant Protection and Land Transformation Criteria for Observing and Measuring Changes Associated with Land Transformation.

Journal ArticleDOI
TL;DR: In this paper, a total of 27 different peat types from Sweden were characterized using principal component analysis (PCA) to probe any relationship between different peAT properties and to group similar peat samples.
Abstract: A total of 27 different peat types from Sweden were characterized. Botanical composition, particle-size distribution, elementary constituents, degree of decomposition, calorific value, and concentrations of monosaccharide, amino sugar, amino acid constituents, and bitumen were determined. Altogether 62 variables were recorded. The results were examined using principal component analysis (PCA) to probe any relationship between different peat properties and to group similar peat samples. The 41 samples separated into eight different groups. The main distinction between these peat samples could be explained by differences in the relative amounts of Carex and Sphagnum remains. Carex plants generally seem to be more chemically transformed through microbial decomposition than the Sphagnum fragments, which, in combination with differences in the original chemical compositions, causes chemical dissimilarities between the peat samples. Differences in the degradation pattern for Sphagnum and Carex peats were found when two separate PCAs on parts of the sample set were made.

Journal ArticleDOI
TL;DR: In this paper, the effect of wetting front depth on the infiltration rate (IR) of Calcic Haploxeralf and Typic Chromoxerert soils was studied under field conditions using a rainfall simulator.
Abstract: The effect of wetting front depth on the infiltration rate (IR) of Calcic Haploxeralf and Typic Chromoxerert soils was studied under field conditions using a rainfall simulator. In both soils the IR decreased more sharply when the wetting front was deeper, but this difference became smaller as the r

Journal ArticleDOI
TL;DR: Stability and certain other characteristics, such as their reusability and their ability to transform xenobiotics as efficiently as the soluble enzyme, should make these laccase complexes useful catalysts of detoxification reactions in soil.
Abstract: We investigated the ability of an immobilized fungal laccase from Trametes versicolor to transform 2,4-dichlorophenol (2,4-DCP), an intermediate of pesticide degradation. Immobilization supports were a silt loam soil and several clays, kaolinite, and two types of smectite, referred to as montmorillonite 1 and montmorillonite 2. The majority of the added laccase activity was immobilized to these supports, using 3-aminopropyltriethoxysilane and glutaraldehyde. The catalytic properties of these laccase-clay and laccase-soil complexes toward the substrate, 2,4-DCP, were assessed using radiolabeled tracer and chromatographic techniques. Incubation of 2,4-DCP with laccase caused the formation of oligomers, which are insoluble in aqueous solutions and can, therefore, be removed. The efficiency of the laccase immobilized on kaolinite and soil to remove 2,4-DCP from solution was similar to that of the free enzyme (approximately 95% of the added 14C-2,4-DCP was removed) and greater than that of the enzyme immobilized on montmorillonites 1 and 2 (69 and 42%, respectively). For these last two supports, however, enzymatic removal may not have been responsible for the entire loss of 2,4-DCP, as adsorption on montmorillonites 1 and 2 also contributed to the observed decreases in 2,4-DCP. A noteworthy advantage of the immobilized laccase over the free enzyme was that it could be separated from the reaction mixture and used repeatedly. After repeated 2-h incubation cycles of the immobilized enzyme with 14C-2,4-DCP, the laccase-kaolinite, laccase-montmorillonite 1, and laccase-soil complexes exhibited only a slight decrease in the ability to remove 2,4-DCP. The possibility of nonenzymatic removal of 2,4-DCP was excluded in experiments performed under anaerobic conditions, in which laccase activity was completely inhibited. The effect of a proteolytic enzyme on the free and immobilized laccase was also tested, and, as a result of their resistance to proteolysis, the immobilized enzyme catalyzed the removal of greater amounts of 2,4-DCP than the free enzyme. This stability and certain other characteristics, such as their reusability and their ability to transform xenobiotics as efficiently as the soluble enzyme, should make these laccase complexes useful catalysts of detoxification reactions in soil.


Journal ArticleDOI
TL;DR: In this article, the root development of wheat (Triticum aestivum cv. Hart) seedlings was measured for 3 d in 20 acidic soil horizons, and root length was related to amounts and forms of Al in soil solution and Al extracted by 0.01 M CaCl2.
Abstract: Short-term bioassay techniques that measure root development of seedlings in soil can be used to evaluate the applicability of chemical methods to predict the Al toxicity of a soil. Wheat (Triticum aestivum cv. Hart) seedlings were grown for 3 d in 20 acidic soil horizons, and root length was related to amounts and forms of Al in soil solution and Al extracted by 0.01 M CaCl2, 1 M KCl, 0.5 M CuCl2, and 0.33 M LaCl3. With the exception of Al extracted by 0.01 M CaCl2, soil extraction methods were not effective in predicting root growth. Root growth was not closely related to total soil solution Al or soil solution Al reacting with 8-hydroxyquinoline, pyrocatechol violet, or aluminon. These colorimetric reagents reacted with nontoxic forms of Al, including organically bound Al, and overestimated the toxic component. Activities of Al species in soil solution were estimated from soil solution composition using the GEOCHEM program. The calculated Al3+ activity ({Al3+}) ranged from 0 to 119 μ M and taken alone was not a good predictor of root growth. It is likely that calculated {Al3+} overestimated actual {Al3+} due to the difficulty of measuring all Al-complexing ligands in soil solution. Root growth in these soils was best described by a multiple regression equation containing soil solution pH, Ca, and Al. The results of this study illustrate the limitations associated with the current methods used to estimate toxic Al levels. New methods are needed to directly measure the toxic Al component or components in soil solution. Until better chemical or instrumental techniques are developed, the short-term bioassay technique should serve as a useful means of assessing the potential Al toxicity of a soil.

Journal ArticleDOI
TL;DR: In this paper, an improved numerical method was proposed to estimate the gas diffusion coefficient (D) of a finite soil sample, giving as a byproduct an estimation of the effective porosity (e).
Abstract: This paper describes an improved numerical method to estimate the gas diffusion coefficient (D) of a finite soil sample, giving as a by-product an estimation of the effective porosity (e). This method is applied to an earlier apparatus used to measure the rate of transfer of tracer krypton-85 through a finite soil sample: the soil sample is enclosed by two gas cells, and the concentration in each gas cell is regularly measured after gas injection using β radiation count rates from the test gas. The proposed numerical approach combines the finite-element method to solve Fick's second law of diffusion, and a nonlinear, iterative procedure to find the estimated parameters &OV0429; and ê, where the residual differences between the measured and simulated count rates at opposite ends of the sample are minimized. An error analysis that takes into account the random process of β emission of tracer is numerically simulated: the gas diffusion coefficient is shown to have a low sensitivity to this source of error, whereas the affective porosity has a larger sensitivity. The proposed method is applied to a large range of soils, including (1) wet and dry undisturbed field soil cores, (2) compacted, water-saturated aggregates, (3) dry and wet textural soil cores. The parameters &OV0429; and ê were fitted satisfactorily to the measured data on each soil sample: the diffusion coefficient estimates are compared with existing estimation methods, whereas the estimated effective porosity is approximately the same when using the iterative proposed approach or a mass balance method applied to the experimental apparatus. Furthermore, it is shown that there is no simple and unique relationship for all the porous media between the calculated gas diffusion coefficient and soil sample air-filled porosity: such a relationship is likely to be highly dependent on the physical characteristics of the pore space, such as pore continuity, tortuosity, and morphology.

Journal ArticleDOI
TL;DR: In this article, EFLUM-ARTICLE-1989-003 Record created on 2005-09-08, modified on 2017-02-23, and used for the first time.
Abstract: Note: 148: 77-86 Reference EFLUM-ARTICLE-1989-003 Record created on 2005-09-08, modified on 2017-02-23

Journal ArticleDOI
TL;DR: In this paper, the effectiveness of several polymer types and a latex emulsion for enhancing seedling emergence, reducing crust hardness, and improving aggregate stability was tested in a laboratory study.
Abstract: Extensive areas of cultivated soil develop crusts that impede seedling emergence. In a laboratory study, we tested the effectiveness of several polymer types and a latex emulsion for enhancing seedling emergence, reducing crust hardness, and improving aggregate stability. Guar (G) and polyacrylamide (PAM) polymers, which were either cationic (C), nonionic (N), or anionic (A), were investigated at applied solution concentrations of 0, 10, or 50 mg L−1. Arlington soil (coarse-loamy, mixed, thermic Haplic Durixderalfs) was used. In the first experiment, both A-PAM and C-G (first letter refers to the charge and the second to the polymer type) significantly (95% confidence level) increased the number of cotton seedling emergence as compared with the control. A-PAM provided for higher seedling emergence than C-G. The penetrometer resistance was in the order: control > C-G > A-PAM, whereas the aggregate stability was in the opposite order. In a second experiment on tomato seedling emergence, penetrometer resistances were in the general order: control > latex > A-G > others, which were about equal. The average tomato seedling emergence was considerably higher for the polymer-treated soil than for the control, but variability precluded the establishment of significant differences between the treatments. The third experiment investigated treatment effects on penetrometer resistance and aggregate stability without seedling emergence. The aggregate stability was in the order: N-PAM > A-G > A-PAM = C-G = N-G = latex > control. When latex was excluded, an inverse relationship (r2 = 0.73) was found between aggregate stability and penetrometer resistance. Treatments did not affect evaporation from the soil in any of the tests.

Journal ArticleDOI
TL;DR: In this paper, the physical and chemical properties of 13 volcanic ash soils from southern Alaska have been studied and compared with Andisols and Spodosols in terms of their morphological properties.
Abstract: Twenty pedons of volcanic ash soils from southern Alaska used in this study have a cryic temperature regime and udic to perudic moisture regimes. They have distinctive morphological properties common to Andisols in many other parts of the world: (1) multisequum with abrupt or clear boundaries, (2) very friable granular structure in A horizons and friable subangular blocky structure in B horizons, and (3) loamy texture with a smeary consistency. They also have distinctive morphological properties common to Spodosols: (1) an organic horizon in all the pedons, (2) an albic or E horizon in most pedons, (3) underlying the E horizon, one or more horizons with hue redder than 10 YR in most pedons, and (4) a placic horizon below the spodiclike horizons in some pedons. The physical and chemical properties of the 13 pedons are presented and discussed. The properties of 7 pedons presented in previous studies are reviewed. All 20 pedons were found to meet the criteria of andic properties, and 19 of them also meet the chemical criteria of a spodic horizon. The pedons were classified according to both Soil Taxonomy and the Andisol proposal. Andisols were proposed to be keyed out after Histosols, but before Spodosols (Leamy 1988). Those Andisols having chemical properties of spodic horizon are differentiated from Spodosols by not having an albic-spodic sequum within the required thickness of horizons with andic properties. A comparison of the two classifications and the implication for soil survey and interpretation are also discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the changes in the diethylenetriaminepentaa-cetic acid (DTPA)-extractable Zn and Cu in 26 acidic to near neutral alluvial soils on submergence and observed that there was always a decrease in their contents.
Abstract: We investigated in the laboratory the changes in the diethylenetriaminepentaa-cetic acid (DTPA)-extractable Zn and Cu in 26 acidic to near neutral alluvial soils on submergence and observed that there was always a decrease in their contents. The percentage of decrease was significantly correlated with initial pH, organic C, clay, cation exchange capacity (CEC), and initial DTPA-extractable contents. The pH seemed to play the most important role in influencing the magnitude of decrease. Multiple regression equations showed that 40.06 and 39.44% variability in the magnitude of decrease of Zn and Cu, respectively, could be accounted for by some of the initial soil properties. On submergence, there was an increase in pH, CO32-, S2-, and DTPA-extractable Fe and Mn. The percentage of decrease in DTPA-extractable Zn and Cu was positively correlated with the magnitude of increase in pH (not with Cu), CO32-, S2-, and Fe and was negatively correlated with Mn. Of the variability in the percentage of decrease in Zn and Cu, 57.30 and 59.30% could be accounted for by the change in these parameters, thus lending support to the hypothesis that the decrease in availability of Zn and Cu in acidic to near neutral soils on submergence is due to their precipitation as hydroxide, carbonate, sulfide, and iron compounds. The results of path coefficient analysis revealed that increase in pH directly contributed 36.96% of the percentage of decrease in DTPA-extractable Zn in soil on submergence. The total contribution of pH, comprising both direct and indirect effects through CO32-, S2-, and Fe, was 56.40%, suggesting that mechanisms other than those mentioned are operative to cause decrease in Zn availability in soils on submergence. Further research is necessary for their elucidation.

Journal ArticleDOI
TL;DR: In this paper, the authors used steam-sterilized soil to test the hypothesis that there is competition between N and Si for plant uptake, and showed that the hypothesis is false.
Abstract: Because vegetative parts of grass species are generally high in Si, monocot and dicot plants were grown in steam-sterilized soil to further test the hypothesis that there is competition between N and Si for plant uptake. Silicon uptake by dicots is low, so the species tested in this study was not se

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the effects of using sewage sludge compost to satisfy the N requirement of crops, which resulted from greenhouse and controlled environmental growth chamber studies, have not been sufficiently validated with field trials.
Abstract: Recommendations for using sewage sludge compost to satisfy the N requirement of crops, which resulted from greenhouse and controlled environmental growth chamber studies, have not been sufficiently validated with field trials. Studies were conducted to evaluate the effects of sewage sludge compost a

Journal ArticleDOI
TL;DR: In this paper, a moving mean slope model (MMS) is proposed for vertical, transient flow of water in unsaturated soil, which uses the slope of the natural log of the hydraulic conductivity (K) versus soil-water potential (ψ) curve as a dynamic parameter.
Abstract: We present a rapid numerical solution for vertical, transient flow of water in unsaturated soil. The model is labeled the moving mean slope model (MMS model), because it uses the slope of the natural log of the hydraulic conductivity (K) versus soil-water potential (ψ) curve as a dynamic parameter. The MMS model is developed from a model for flow in homogeneous, relatively wet soils presented by Wind and von Doorne (1975). The model can simulate transient flow in homogeneous and heterogeneous soils correctly for any rang e of soil-water content. This has been validated against semianalytical solutions and solutions obtained with traditional finite-difference and finite-element models. A Courant number analysis method is presented to make direct comparisons of criteria for avoiding numerical errors for the MMS model compared with traditional finite-difference models. For coarse-textured soils, the MMS model uses about the same computer time as the traditional finite-difference and finite-element models. For soils ranging from fine-textured to medium-textured, the MMS model is one to several orders of magnitude faster than the traditional numerical models.

Journal ArticleDOI
TL;DR: The productivity of 22 soils on serpentinized peridotite, as determined by either the Dunning site index (DSI) for mixed conifers or the timber yield index (TYI), is more closely related to the surface Ca/Mg ratio in either ammonium acetate or citrate-dithionite (CD) extracts than to any combination of climatic and physical soil variables or to the Fe, Mn, Cr, Ni, or Co contents in CD extracts as discussed by the authors.
Abstract: The productivity of 22 soils on serpentinized peridotite, as determined by either the Dunning site index (DSI) for mixed conifers or the timber yield index (TYI), is more closely related to the surface (0 to 30 cm) soil Ca/Mg ratio in either ammonium acetate or citrate-dithionite (CD) extracts than to any combination of climatic and physical soil variables or to the Fe, Mn, Cr, Ni, or Co contents in CD extracts. The coefficient of determination of an equation for the TYI as a function of the exchangeable Ca/Mg ratio is 0.87, increasing to 0.93 upon adding a function of the plant-available-water capacity (AWC) in 1 m of soil. Manganese is the only transition element whose content in CD extracts is correlated significantly with the DSI or the TYI, and that correlation appears to be fortuitous. The soil organic carbon content in 0.6 m of soil is a function of productivity, or the TYI (r2 = 0.53).

Journal ArticleDOI
TL;DR: In this paper, the root growth of soybean was studied in dilute nutrient solution containing 2.0 g L−1 PG without the addition of Al or in solutions containing 40 μM Al.
Abstract: The use of gypsum or phosphogypsum (PG) as an ameliorant of subsoil acidity has been reported. However, the role of these amendments in aluminum (Al) speciation and solubility is not clearly understood. We studied the root growth of soybean [Glycine max (L.) Merr.] cv. Lee in dilute nutrient solution containing 2.0 g L−1 PG without the addition of Al or in solutions containing 40 μM Al without any amendments or with the addition of PG, CaSO4. 2H2O, or CaSO4. 2H2O plus varying concentrations of P and F. The prediction of Al speciation by using the GEOCHEM computer program revealed that in solutions containing F∼, either added as NaF or as impurities in the PG, Al was entirely complexed with F∼. The addition of CaSO4. 2H2O (2.07 g L−1) to a solution containing 40 μM Al decreased the predicted activity of Al3+ from 36 to 11% and increased that of AlSO4+ from 33 to 80%, while the total root length of soybean increased by about fourfold. Addition of PG (2 g L−1) to a solution containing no Al decreased the total root length by 14%. Root growth was very similar in PG-amended solutions with or without the addition of 40 μM Al. The addition of 400 μM F∼ as NaF to Al solutions amended with CaSO4. 2H2O seemed to decrease root growth as compared to that in solutions amended with CaSO4. 2H2O without the addition of F∼. Root growth was very poorly related to the sum of predicted activities of Al monomers. Aluminum measured by the modified aluminon technique (without preacidification and preheating of the solution; 30-min reaction time) failed to exclude Al complexed with SO42- and F∼, which are less phyto-toxic. Therefore, this measure of Al showed a poor relationship with root growth response. On the contrary, Al measured by the modified 8-hydroxyquinoline technique (15 s reaction) excluded about 92% of Al complexed with F∼, although it failed to exclude Al complexed with SO42-. Thus, both of the Al assay techniques used in the present study are poor indicators of Al toxicity when the SO42- ligand plays a major role in the alleviation of Al toxicity. However, Al measured by the modified 8-hydroxyquinoline technique was a better indicator than that measured by the modified aluminon technique when the F∼ ligand was responsible for the alleviation of Al phytotoxicity.

Journal ArticleDOI
TL;DR: In this paper, the chemical significance of PCO2 buildup, visa-vis reduction in soil pH and sodicity on the associated increase in hydraulic conductivity (HC) for rice culture conditions was evaluated.
Abstract: In a laboratory study we evaluated the chemical significance of PCO2 buildup, visa-vis reduction in soil pH and sodicity on the associated increase in hydraulic conductivity (HC) for rice culture conditions. Soil HC was determined at constant hydraulic head in soil columns packed to a bulk density of 1.47 g cm−3 and flushed with CO2 to obviate air entrapment in the presence and in the absence of farmyard manure (FYM) and rice. Hydraulic conductivity of alkali soils generally was least improved by continuous submergence, but was more improved in FYM-treated soils. Growing rice further increased the HC of soils. Exchangeable Na removal and reductions in pH appear to be directly related to the amount of CO2 production in calcareous strongly alkali soils. It seems that the physical presence of an active root system yields a certain HC, but chemical reclamation is primarily through more CO2 production. Organic manures improve rice growth because they raise PCO2 to reduce pH and sodicity through greater mobilization of soil lime.