Showing papers in "Soil Science in 1980"

Macromolecular Structures of Humic Substances

Abstract: We investigated humic substances by surface pressure and viscosity measurements at different pHs and neutral salt concentrations to elucidate their macromolecular configurations. We observed that such configurations were not unique; they varied with the changes in the medium. The controlling

Quantities of Plant Nutrients in the Microbial Biomass of Selected Soils

Abstract: To obtain general information on the quantities of mineral nutrients in the microbial biomass of soils, we determined the carbon content of the microbial cells of 29 soils Carbon data were converted to nutrient values using C to N, C to P, C to K, and C to Ca ratios established by measuring (1) the average C to mineral content of pure cultures of 24 species of soil microorganisms and (2) the relative contributions of bacterial and fungal cell populations to the microbial biomass of 17 soils. The biomass in 26 agricultural soils contained between 0.27 and 4.8 percent of the total soil C (x ≅ 2 5 percent) and between 0.50 and 15.3 percent of the total sell N (x ≅ 5 0 percent). The average quantities of N, P, K. and Ca in the microflora of the soils (upper 12.5 cm) were about 108, 83, 70, and 11 kg ha -1 , respectively. In the L + F + H layers of three forest soils, between 0.52 and 0.91 percent of the total C and 0 16 and 0.22 percent of the total N were in the microbial biomass.

Chemical Changes Due To Acid Precipitation In A Loess-Derived Soil In Central Europe

Abstract: In a stand of Fagus silvatica in the Solling highlands, Federal Republic of Germany, we followed the effect of acid precipitation on chemical soil state and the ion fluxes in the ecosystem between 1966 and 1979. As indicated by increasing aluminum concentration in the soil solution and an in

Properties and Management of Forest Soils

Abstract: PROPERTIES AND DYNAMIC PROCESSES: Introduction Forest Soils and Vegetation Development Soils Associated with the Major Forest Ecosystems The Forest Floor Forest Soil Biology Chemical Properties of Forest Soils Physical Properties of Forest Soils Soil Water and the Hydrological Cycle Soil and Roots Mycorrhizae: Forms and Functions Nutrient Cycling in Forest Ecosystems Soil Properties and Site Productivity MANAGEMENT AND ITS CONSEQUENCES: Forest Land Inventory Soils and Silviculture Management of Nursery and Seed Orchard Soils Management of Problem Soils Tropical Forest Soils Diagnosis and Correction of Nutrient Deficiencies Fertilizer Materials and Application Systems Effects of Anthropogenic Chemicals on Forest Ecosystems Effects of Fire on Soils and Site Intensive Management and Long-Term Soil Productivity Appendixes

Scanning electron microscope observations on soil crusts and their formation.

Abstract: Scanning electron micrographs (SEM) of crusts of loessial soils are presented. SEM observations were performed on crusts formed by raindrop impact at various stages of their formation. The crust structure was compared to the natural undisturbed soil. During the crust formation, a middle-term stage developed at which coarse particles, stripped of the fine ones, composed the surface layer of the soil. At the final stage of the crust formation, the coarse particles were washed away, and a thin seal skin, about 0.1 millimeter thick, formed the uppermost layer of the soil. A depositional crust, which was formed mainly by the translocation of fine particles, was marked by the presence of a thin skin also about 0.1 millimeter thick, suggesting involvement of similar secondary mechanisms of formation. This work illustrates the use of SEM for the study of soil crust formation and structure.

Preferential Reduction of Amorphous to Crystalline Iron Oxides by Bacterial Activity

Abstract: Reduction of pedogenic iron oxides by the activity of Clostridium butyricum was studied in model experiments under controlled conditions of pH, particle size (63 to 125 μm), glucose (2 percent), and anaerobic conditions. Three horizons—from a gley, pseudogley, and red clay soil, respectively—with different Feo:Fed ratios were selected as test material. Except for Fe(II) formation, pH and Eh were measured at regular intervals. In all soils the total amount of free iron oxides (Fed), as well as the crystalline Fe (Fed - Feo), decreased while Fe(II) increased. The amount of amorphous Fe (Feo) remained relatively constant in those soils low in Feo:Fed (0.1 to 0.19), but diminished in the sample with a relatively high amount of amorphous Fe (Feo:Fed = 0.78). This suggests that crystalline rather than amorphous Fe forms are dissolved preferentially by acting as terminal electron acceptors. Nevertheless, the reduction of crystalline 59Fe-labeled oxides (hematite and goethite) mixed with Fe-amorphous gley soil material (Feo:Fed = 0.78) clearly showed that oxalate-soluble Fe was attacked in preference to 59Fe-labeled crystalline Fe. The processes of Fe(III) reduction in a microsite are discussed in relation to the mechanism of Fe(II) formation in flooded soils.

Effect of Solar Heating of Soils by Transparent Polyethylene Mulching on Their Chemical Properties

Abstract: Solar heating of soils by mulching with transparent polyethylene during the hot season results in increased soil temperatures and the killing of certain pathogens. Mulching increases temperatures by up to 10 to 12°C in the upper soil layer. We studied the effect of this treatment on the chemical properties and hydraulic conductivity (HC) of soil. Field experiments showed enhanced plant growth in solar heated soils, even in the absence of known pathogens. Saturated extracts of the upper soil layers of eight different solar heated soils showed increased concentrations of soluble organic matter and minerals. The greatest increase was in NO3- concentration; NH4+, K+, Ca2+ + Mg2+, and Cl- were also found to increase. Changes in soil pH, total organic matter, NaHCCv extractable P, and HC were small or inconsistent. Tomato seedlings grown on extracts of heated soils showed enhanced growth in comparison with seedlings grown on extracts of unheated soils.

A single-extraction method using silver-thiourea for measuring exchangeable cations and effective cec in soils with variable charges

Abstract: The use of a single extraction with dilute unbuffered silver-thiourea (AgTU) solution (0.01 M Ag+) for measuring exchangeable cations and the cation exchange capacity (CEC) of soils was compared with the conventional effective CEC method, which used N NH4OAc displacement for exchangeable “ba

Trace Element Accumulation, Movement, and Distribution in the Soil Profile from Massive Applications of Sewage Sludge

Abstract: Sewage sludge was added annually, for a 3-year period, to a series of field plots. Application rates varied from 0 to 225 metric tons per hectare per year. The sludges were mixed into the surface 20 centimeters of soil and, in general, increased the amounts of HNO3-extractable heavy metals.

Soil-oxygen effects on stomatal response.

Abstract: We reviewed and compared several greenhouse studies on the effects of low soil oxygen (O2) levels upon plant response. The studies are discussed with particular reference to stomatal closure. Both indirect and direct observations of stomatal closure at low soil O2 diffusion rates (ODR) were compiled. Plant response was similar over a wide range of species, including tomato (Lycopersicon esculentum), sunflower (Helianthus, sp.), jojoba (Simmondsia chinensis), cotton (Gossypium hirsutum and G. barbadense), and wheat (Triticum aestivum). The studies reviewed indicate that elimination of soil O2 from the profile can cause stomatal closure even at optimum matric potentials. When ODR dropped below 20 x 10−8 g.cm−2 sec−1, leaf diffuse resistance rose as an exponential function in all the species observed. In some of the studies, photosynthesis and water use were observed to drop when ODR fell below 20 x 10−8 g.cm−2 sec.−1 Whereas stomatal response to low soil O2 levels was highly consistent, the effect of low soil O2 on plant water potential was not. This suggests that theories pointing to increased root resistance resulting from low soil O2 as the cause of stomatal closure do not fully explain some of the observed data. This in turn suggests that stomatal response under the described conditions may not be entirely a passive mechanical response.

Effects of topsoil storage during surface mining on the viability of VA mycorrhiza

Abstract: Storing topsoil for 3 years was shown to reduce substantially the levels of viable inocula relative to levels in adjacent, undisturbed prairie soils. The detrimental effect of storage on VA mycorrhiza is associated with the loss of viability of mycorrhizal fragments occurring in the stored soil. Data are also presented supporting an interaction between infected root segments and roots of uninfected plants as a major means of spreading mycorrhiza in these soils.

Plant root growth in acid Andosols from northeastern Japan : 2. Exchange acidity Y1 as a realistic measure of aluminum toxicity potential

Abstract: Chemical and greenhouse studies were conducted to show that exchange acidity Y1, determined by titration of 125 ml of N KC1 soil extract (soil:N KC1 = 100:250) with 0.1 N NaOH, was a useful, realistic measure of aluminum toxicity potential in acid Andosols from northeastern Japan. Twenty-eig

Nonsymbiotic Nitrogen Fixation Associated With The Rice Plant In Flooded Soils

Abstract: Nitrogen balance studies based on Kjeldahl data are reported for several crops of rice (Oryza sativa) grown in continuously flooded soil in pots under greenhouse conditions in the Philippines. Flooded soil planted to rice had a statistically significant positive nitrogen balance. The positiv

The Release of Silicon, Aluminum, and Potassium during Decomposition of Soil Minerals by Humic ACID1

Abstract: Decomposition of primary minerals by humic and fulvic acids was investigated by shaking microcline, biotite, or muscovite with soil humic solutions at pH 7.0 and 2.5 for 0 to 1000 hours. Silica, aluminum, and potassium released by the primary minerals were determined in the extracts by atomi

Influence Of Phosphorus And Zinc Application On The Availability Of Zinc, Copper, Iron, Manganese, And Phosphorus In Waterlogged Rice Soils

Abstract: Laboratory incubation experiments were conducted with three clay loam, lowland rice soils (Haplustalf) to study the effect of applying three different levels of phosphorus (0, 50, and 100 ppm) and zinc (0, 5, and 10 ppm), in all possible combinations, on the changes in DTPA-extractable zinc, copper, iron, and manganese wand Bray's 2 extractable phosphorus in soil. We sought to understand whether the effect of such interaction is responsible, at least partly, for the decreased uptake of some of the nutrient elements in rice on phosphorus and zinc fertilization, as reported by others. The results showed that applying phosphorus decreased the content of DTPA-extractable Zn, Cu, Fe, and Mn in soils, the rate of decrease gradually declining with the progress of the incubation period. The depressive effect of P on extractable Zn content was found to be more prominent in respect of soil native Zn than of the applied one. Application of Zn also depressed the content of extractable Cu, Fe, and P, but increased that of extractable Mn. The decrease in the uptake of Zn or P, Cu, and Fe by rice, resulting from the application of P or Zn as reported by others, was attributed at least partly to the decrease in the availability of these elements in soil.

Adsorption of some nitrogenated herbicides by soil humic acids

Abstract: We studied the adsorption of two s-triazine and two substituted urea herbicides by three different soil humic acids, using elementary analyses and infrared spectroscopy.Obtained data show that adsorption occurs in all cases, involving such mechanisms as ionic bonds, only for the s-triazines;

Estimation of soil-moisture characteristics from mechanical properties of soils.

Abstract: Soil-moisture characteristics can be established directly from the physical properties of soils and a single measurement of water potential, φ, in bars, at some moisture content, φ, on a volume basis. The method is applicable for those soils for which the φ - θ relations can be expressed as

Advanced Chemical Methods for Soil and Clay Minerals Research

Abstract: 1. Mossbauer Spectroscopy.- 1-1. Introduction to the Mossbauer Effect.- 1-2. Basic Principles of Mossbauer Spectroscopy.- 1-3. Instrumentation and Experimental Procedures.- 1-4. Application of Mossbauer Spectroscopy to the Study of Silicate Minerals.- 1-5. The Study of Mineral Alteration Reactions.- 1-6. Iron Oxides and their Characterization in Soils.- 1-7. Critical Assessment of the Potential of Mossbauer Spectroscopy, and its Application to Nuclei Other than Iron.- References.- 2. Neutron Scattering Methods of Investigating Clay Systems.- 2-1. Introduction.- 2-2. Elementary Neutron Scattering Theory.- 2-3. Neutron Scattering Instrumentation and Methods.- 2-4. Applications of Neutron Spectroscopy to Studies of Clay Minerals.- Appendix 2-1. Macroscopic Cross Section for a Montmorillonite-Water System.- Appendix 2-2. Calculation of Incoherent Scattering Intensity Ratios for a Clay-Water System.- References.- 3. Introduction to X-ray Photoelectron Spectroscopy.- 3-1. Introduction.- 3-2. Trend of XPS Spectra.- 3-3. Instrumentation.- 3-4. Peak Position.- 3-5. Explored Depth.- 3-6. Peak Intensity.- 3-7. Overview of Methods of Characterization of Solids Based on X-ray, Electron and Ion Beams.- References.- 4. Application of X-ray Photoelectron Spectroscopy to the Study of Mineral Surface Chemistry.- 4-1. Uniqueness of XPS for the Investigation of Mineral Surface Phenomena - Probing Depth.- 4-2. Sample Handling Techniques.- 4-3. Analytical Applications.- 4-4. Electron Take-Off (Grazing) Angle Analysis Applications.- 4-5. Qualitative Bonding Investigations.- 4-6. Summary.- References.- 5. The Application of NMR to the Study of Clay Minerals.- 5-1. Introduction: Fundamentals of NMR.- 5-2. The Bloch Equations.- 5-3. Line Shape.- 5-4. Relaxation Mechanisms.- 5-5. Review of Some Problems: Order and Disorder in Adsorbed Water Molecules.- References.- 6. Distribution of Ions in the Octahedral Sheet of Micas.- 6-1. Introduction.- 6-2. Influence of the Fe2+ Ions.- 6-3. H+ Spectra of Phlogopites.- 6-4. H+ Spectra of Biotites.- 6-5. F? Spectra.- 6-6. Correlation with I.R. Results.- References.- 7. General Theory and Experimental Aspects of Electron Spin Resonance.- 7-1. Introduction.- 7-2. G-Factor Tensor.- 7-3. Hyperfine Interaction.- 7-4. Analysis of ESR Spectra.- 7-5. Fine Structure.- 7-6. Summary.- Appendix 7-1.- Appendix 7-2.- Appendix 7-3.- References.- 8. Applications of ESR Spectroscopy to Inorganic-Clay Systems.- 8-1. Introduction.- 8-2. Surface-Bound Metal Ions.- 8- 3. Framework Paramagnetic Centers.- References.- 9. Application of Spin Probes to ESR Studies of Organic-Clay Systems.- 9- 1. Nitroxide Spin Probes - Origin of the ESR Spectrum.- 9-2. Nitroxides in Low-Viscosity Media - Rapid Isotropic Motion.- 9-3. Nitroxides in High-Viscosity Media.- 9-4. Nitroxides Adsorbed on Clay Surfaces.- 9-5. Experimental Considerations in Using Nitroxide Spin Probes.- References.- 10. Applications of Photoacoustic Spectroscopy to the Study of Soils and Clay Minerals.- 10-1. Introduction.- 10-2. Instrumentation.- 10-3. Results.- 10-4. Conclusions.- References.

Interaction of Selenium and Sulfur on the Growth and Chemical Composition of Raya

Abstract: Variable selenium (Se) concentration effects in sand culture and sandy soils were studied on raya (Brassica juncea Coss.), an oil crop, in the greenhouse. The sand cultures were supplied with Se at rates of 0, 0.5, 1, 2, 4, 8, 16, and 32 parts per million (ppm), whereas the sandy soil was tr

Sorption of Benzidine by Sediments and Soils

Abstract: We examined the effects of soil and sediment properties on the sorption of benzidine. Batch equilibrium sorption isotherms were determined for 14 soil and sediment samples. The sorption isotherms were nonlinear and were well represented by the Freundlich equation, with 1/n values averaging approximately 0.5. Sorption was largely controlled by the pH of the aqueous phase. Benzidine sorption was corrected for sorption of the neutral species by organic matter, and sorption of the ionized species was found to be highly correlated with surface area of the soil or sediment.

Movement of 2,4,5-T Through Large Soil Columns

Abstract: The movement of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) through large soil columns was measured and simulated by means of a model that incorporates adsorptiondesorption and biological degradation processes. Water(3H) and 2,4,5-T (14C) distributions with depth were calculated after each of several irrigations and compared with concentrations of the isotopes measured in soil solution samples collected at several depths via suction cups inserted into the soil columns. The model successfully predicted tritiated water distributions after several irrigations and adequately predicted herbicide concentrations after the first irrigation. Nevertheless, predicted herbicide concentrations in the soil solution after the second and subsequent irrigations were much greater than observed values.

Effects of soil temperature, moisture, and air-drying on extractable manganese, iron, copper, and zinc

Abstract: Soil samples for microelement extraction are often taken with little regard to field moisture content and stored under a variety of conditions. In order to study the effects of these practices on extractable microelements, we incubated three soils for 2 weeks at various temperatures and moisture contents. The temperatures were 10, 25, and 40°C, and the moisture levels were 5, 1/3, and 0 bars tension. The soils were extracted for diethylenetriamine pentaacetic acid manganese, iron, copper, and zinc after air-drying, as well as in the moist state. Extractable Mn, Fe, and Cu increased with increased temperatures when the soils were incubated at the 0-bar moisture level. Temperature had no effect on these elements at the dryer moisture levels. Increased temperatures decreased Zn extractability in many cases for samples air-dried prior to extraction. Large increases in extractable Mn and smaller increases in Fe and Cu resulted when soils were incubated at 0-bar moisture. Changes in the extractable Mn, Fe, and Cu between the two drier moisture levels were mostly nonsignificant. Extractable Zn decreased with increasing moisture levels. Air-drying the soils prior to extraction caused increased extractable Mn and Fe, when compared with moist extraction at the lower two incubation moisture levels, but at the 0-bar level this pattern was reversed. Extractable Cu and Zn increased upon air-drying the samples prior to extraction, as compared with moist extraction, in nearly every case. Varying temperature and moisture caused significant changes in the extractability of all the microelements studied. The effect of air-drying increasing extractability at low incubation moisture and decreasing extractability at high moisture is particularly important. The conditions of soil moisture prior to air-drying may influence the effects of air-drying on extractable soil microelements.

Yield and Cadmium Content of Rice Grain in Relation to Addition Rates of Cadmium, Copper, Nickel, and Zinc with Sewage Sludge and Liming

Abstract: A greenhouse experiment was conducted with an acid soil, with and without lime, pretreated with cadmium at rates up to 10.0 micrograms per gram of soil in factorial combination with low to high amounts of copper, nickel, and zinc. The treated soils were placed in sealed pots, flooded, and cr

Relation of available soil nitrogen to rice yield.

Abstract: Thirty-one surface soil samples from nine years of rate and ratio rice fertilization experiments at different locations in Louisiana were analyzed for their available-nitrogen content, using six chemical and two biological extraction methods. The relationship between the available soil nitrogen and rough rice yields was then investigated. Total soil nitrogen varied widely, ranging from 540 to 5460 parts per million. The average percentage recovery of total soil nitrogen (representing the available soil nitrogen), as determined by the various methods used, also ranged widely, from as high as 16.74 percent, by the hot alkaline permanganate method, to the lowest value of 1.08 percent, by boiling soils in 0.01 M CaCl2 solution. Good correlation coefficients were obtained, especially among the anaerobic incubation and each of the other extraction methods used. The acid hydrolysis method correlated the least with the other extraction methods. Highly significant correlation coefficients were obtained between the rough rice yields from the untreated plots (plots that received no nitrogen) and the available soil nitrogen determined by all the extraction methods. The best correlation was obtained with the anaerobic incubation method (r = 0.622). The rough rice yield in plots receiving 56 or more kilograms of nitrogen per hectare did not exhibit a significant relationship with the available soil nitrogen. Relationships between the rough rice yields at zero and 28 kg/ha N and the available soil nitrogen, as determined by the anaerobic incubation method, were better described by curvilinear models than by linear ones. The relationship was also established between yield increase from application of 112 kg/ha N (the level of nitrogen generally considered near optimum for rice in Louisiana) and available soil nitrogen determined by the anaerobic incubation method. With some reasonable degree of accuracy, yield increase could be predicted from the graph signifying this relationship.

Transport and Transformation of Methyl Bromide in Soils

Abstract: Although methyl bromide (CH3Br) is used extensively as a soil fumigant, quantitative descriptions of its behavior after fumigation are limited. Methyl bromide undergoes a variety of processes, such as sorption and dissolution, and irreversible sink processes, such as hydrolysis. To evaluate these simultaneously occurring processes, a miscible displacement technique was used in which a pulse of pure CH3Br gas was passed through 10-centimeter-long soil columns at flow velocities ranging from 6 to 60 centimeters per hour (cm h-1). The concentration of the effluent gas was measured using gas chromatography. Experiments were conducted at one flow rate on dry sand, moist sand, a loam, and a peaty muck soil to determine the effect of water, clay minerals, and organic matter on the reversible sink processes. Additional experiments were conducted on Yolo loam at four different flow velocities to determine the effect of flow rate on the reversible sink terms. Mathematical models of transport and transformation of a reactive gas were evaluated by fitting calculated to measured effluent curves. A first-order kinetic model for the reversible sink term more adequately described effluent curves than did a linear, equilibrium model, although both models were apparently inadequate in completely describing the adsorption-desorption process. Irreversible sink processes had negligible effect on the quantitative description of the flow of gas in the columns. Although the rate of transformation of CH3Br gas to Br− had negligible effect on the shape and position of effluent curves, rates of Br− production were significant and influenced by soil type, as determined from incubation experiments. Rates of Br− production were greatest with muck, intermediate with loam, and least with sand.

Solute transport through soil with adsorption and root water uptake computed with a transient and a constant-flux model.

Abstract: Computer models are often used to simulate solute transport through soil profiles. This paper compares the results obtained with two such models. The first model is rather complex and requires a complete description of the soil hydrological properties. The second model is much simpler and uses an average percolation rate as input. Solute transport was compared with and without adsorption and with and without root water uptake. The results show that the relative solute concentration at a given soil depth, as a function of cumulative drainage of an intermittently irrigated soil, is a smooth curve, which can also be simulated with the simple model. Such models are apparently appropriate for predicting solute transport through field soils with their inherent spatial variability in physical and chemical properties.

Denitrification as a Pathway for Nitrate Removal from Organic Soils

Abstract: Potential denitrification rates of a cultivated, drained Everglades Histosol, Pahokee muck (a Lithic medisaprist), were examined to determine their variation with crop and position in the soil profile. The average rates, as measured with a flooded-soil technique in soil samples collected at monthly intervals between July 1977 and August 1978 from a fallow (bare) field at two depths, 0 to 10 cm and 60 to 70 cm, were 2.02 and 0.99 micrograms of nitrogen per cubic centimeter per day, respectively. As a comparison, the mean rates in soils cropped to sugarcane (Saccharum spp. L.) and St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntz), similarly collected and assayed, were 7.21 and 7.27 micrograms of nitrogen per cubic centimeter per day, respectively. Although the relationship among the rates measured from the different soils remained the same, higher values were obtained if nitrous oxide production in nitrate-amended soil in the presence of acetylene was used to estimate denitrification rate. The differences between the two values resulted from variation in the atmosphere of the incubation vessels. The increased denitrification rates of the cropped soil likely reflected the greater availability of organic carbon and increased microbial activity in them. Linear correlation analysis of the data indicated no significant relationship between the initial number of denitrifying bacteria and the denitrification rate.

Plant root growth in acid andosols from northeastern japan: 1. Soil properties and root growth of burdock, barley, and orchard grass

Abstract: This study was conducted to determine the properties of selected Andosols from northeastern Japan and the factors affecting the root growth of burdock, Arctium lappa cv. Takinogawa; barley, Hordeum vulgare cv. Norin-24; and orchard grass Dactylis glomerata cv. Kitamidori grown on these soils in a greenhouse. According to the clay mineralogical composition, the Andosol samples were divided into chloritized 2:1 mineral soils and allophane-imogolite1 soils. All the samples were poor in exchangeable bases, showed pH(H2O) ranging from 4.6 to 5.1, and were rich in reactive aluminum, as indicated by high pH(NaF), existence of large amounts of dithionite-citrate-soluble aluminum, and high phosphate absorption. On the other hand, a wide variation of exchange acidity Y1, determined by the titration of 125 ml of N KCl extract (soil: N KCL = 100:250) with 0.1 N NaOH, was observed; this was very large for chloritized 2:1 mineral soils and negligibly small for allophane-imogolite soils. Root growth of the test plants was reduced in chloritized 2:1 mineral soils, but not in allophane-imogolite soils. Morphological observation and aluminon test of the plant roots showed that aluminum toxicity occurred only in chloritized 2:1 mineral soils, even though all the soils contained large amounts of reactive aluminum and showed pH(H2O) range of 4.6 to 5.1. The degree of reduction of the root yields and the degree of aluminon reaction of aluminum-injured roots were in this order: burdock > barley > orchard grass. Examination of the properties of the soils sampled suggested that exchange acidity Y1 defined by Daikuhara (1914) was a realistic measure of aluminum toxicity potential in Andosols from northeastern Japan.