Cation treatment and drying‐temperature effects on nonylphenol and phenanthrene sorption to a sandy soil

The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na⁺, Ca²⁺, or Al³⁺ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na⁺ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca²⁺ and Al³⁺ decreased it. The ¹H‐NMR relaxometry analyses showed that Al³⁺ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca²⁺ or Na⁺. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.     

土壤有机矿质复合体研究──X.有机矿质复合体转化的初步研究

本文研究铁键、铝键、钙键复合体与溶液中Ｃａ＾２＋、Ｆｅ＾３＋、Ａｌ＾３＋金属离子的相互作用,结果显示,复合体上键合的Ｆｅ＾３＋,不能被溶液中的Ｃａ＾２＋、Ａｌ＾３＋置换,复合体上键合的Ａｌ＾３＋仅少量被Ｆｅ＾３＋、Ｃａ＾２＋置换进入溶液,复合体上键合的Ｃａ＾２＋则可较多地被Ａｌ＾３＋、Ｆｅ＾３＋置换进入溶液,置换的量与ＰＨ及粘土矿物类型有一定关系,尽管复合体上键合的Ｆｅ＾３＋、Ａｌ＾３＋、Ｃａ＾３     

A Study on Fluoride Sorption by Montmorillonite and Kaolinite

Fluoride (F) sorption by acidified montmorillonite, montmorillonite and kaolinite has been investigated as a function of period of agitation, pH, initial fluoride concentration and clay amount. In case of montmorillonite and kaolinite, F sorption is insignificant at pH > 7, while it is maximum at pH 4. Enhanced F sorption by acidified montmorillonite is noted at pH < 10, maximum being at pH 6. Significant concentration of Al³⁺,Fe³⁺ and silica are released from acidified montmorillonite lattice (pH ≈ 2; 1:10 w/v), which decreased considerably owing to the formation of hydroxy (Al and Fe) silicates on subsequent base addition. Soluble fluoro-complexes at pH ≈ 2 and chemical interaction of F with hydroxy (Al and Fe) silicates at pH > 4, are potent sink for F in case of acidified montmorillonite. Soluble fluoro-complexes are also detected in case of montmorillonite and kaolinite at pH ≈ 4. Saturation indices (SIs) for acidified montmorillonite, over the studied pH range (2–10) has also been computed.     

Toxicity factors in acidic forest soils: attempts to evaluate separately the toxic effects of excessive Al3+ and H+ and insufficient Ca2+ and Mg2+ upon root elongation

The acidic soils of temperate forests and some pastures on former forest land characteristically contain large amounts of aluminium and hydrogen ions and small amounts of calcium and magnesium ions. The relative importance of these potential toxicity factors are assessed from published data from soils collected in the United States and Europe. Activities of ions in the soil solutions and at the surfaces of root‐cell plasma membranes were computed with electrostatic models. Activities of Al³⁺ in soil solutions ({Al³⁺}) peaked at pH 4.1, and Al³⁺ activities at the surface of the plasma membrane ({Al³⁺}₀) achieved a broad maximum between pH 4.1 and 4.8; thus, Al³⁺ intoxication is likely to be more severe in soils at pH 4.1 than in more acidic ones. Intoxication (assessed by root elongation) correlated somewhat ambiguously with ion activities, but Al³⁺‐ and H⁺‐induced depletion of Ca²⁺ and Mg²⁺, or both, from the cell surface appears to play a role in toxicity. By contrast, experiments in solution culture, where intercorrelation among {Al³⁺}, {H⁺}, and {Ca²⁺} could be avoided, clearly demonstrated the following extrinsic and intrinsic effects. 1 The ions Al³⁺ and H⁺ are intrinsic toxicants. 2 They are also extrinsic toxicants because of the electrostatic displacement of Ca²⁺ from the surface of the plasma membrane. 3 They are extrinsic ameliorants because each electrostatically displaces the other from the surface of the plasma membrane. 4 The ion Ca²⁺ is an extrinsic ameliorant because of the electrostatic displacement of Al³⁺ and H⁺ from the surface of the plasma membrane. 5 It is an intrinsic ameliorant of intrinsic H⁺ toxicity, but not intrinsic Al³⁺ toxicity. 6 It meets an intrinsic requirement. 7 The ion Mg²⁺ resembles Ca²⁺ in item 4 but not items 5 and 6 in short‐term cultures. In acidic soils, Al³⁺ may prevent H⁺ from becoming an intrinsic toxicant (item 3) and may induce an insufficiency of Ca²⁺ and Mg²⁺ (item 2). These findings have implications for the mechanisms by which woodland plants tolerate very acidic soils.     

THE EQUILIBRIA OF K:Al EXCHANGE IN CLAY MINERALS AND ACID SOILS1

Conventional K: Al exchange isotherms for montmorillonite showed that Al³⁺ was strongly preferred to K⁺ in o-oin solutions. The exchange coefficient, K', calculated using the isotopically exchangeable K, was greater than unity and did not vary with the Al-saturation or with the initial pH of the AlCl₃ solutions. Isotherms for vermiculite, illite, and soils in o·oin solutions also showed Al³⁺-preference but unlike those for montmorillonite were not asymptotic to q_Al/q_o= 1, q_Al being the amount of adsorbed Al and q_o the total adsorbed (Al + K), indicating that some of the isotopically exchangeable K could not easily be exchanged by Al³⁺ ions; this difficultly exchangeable K (DEK) was estimated for each exchanger. K' values for vermiculite, illite, and soils were less than unity and did not vary with Al-saturation or initial pH if the isotopically exchangeable K was corrected for DEK. This showed that K⁺ was adsorbed more strongly than Al³⁺. Strengths of K⁺ adsorption referred to Al³⁺ as the counter-cation were in order: soils > vermiculite, illite > montmorillonite.     

CALCIUM: ALUMINIUM EXCHANGE EQUILIBRIA IN CLAY MINERALS AND ACID SOILS1

Exchange reactions between 0.0in AlCl₃ solutions of different pH and Ca-saturated montmorillonite, vermiculite, illite, and soils from the Park Grass Experiment at Rothamsted and the Deerpark Experiment, Wexford, Ireland, showed that Al³⁺ and Al(OH)₂⁺ were adsorbed from solutions of pH > 4.0 and Al³⁺ and H⁺ from solutions of pH < 3.0. When Al was adsorbed, the cation exchange capacity of Ca-saturated soils and clays increased. Conventional Ca: Al exchange isotherms showed that Al³⁺ was strongly preferred to Ca²⁺ on all soils and clays. The equilibrium constant for Ca: Al exchange, K, was identical for soils before and after oxidizing their organic matter and did not vary, for any exchanger, with Al-saturation or the initial pH of the AlCl₃ solution. This proved the validity of the procedure used for calculating exchangeable Al³⁺. K values for Ca:Al exchange favoured Al³⁺ in the order: vermiculite > Park Grass soil > Deerpark soil > illite > montmorillonite. The influence of surface-charge densities of the clay minerals on this order is discussed and a method proposed and tested for calculating the K value of a soil from its mineralogical composition.     

电解质种类和浓度影响磷酸根解吸的机理研究

本文研究了吸附性阳离子、电解质浓度和组成影响几种矿物和土壤吸附态磷的解吸的机理。结果表明,吸附性阳离子影响磷酸根解吸与离子桥有关。桥接静电场愈强,被束缚磷的释放就愈困难。电解质阳离子对磷酸根解吸的影响则取决于其对表面负电荷的屏蔽效应。阳离子电价高,屏蔽作用大,磷解吸就少。电解质浓度影响吸附态磷的解吸主要与表面电位的变化有关。当pH>PZC值时,提高电解质浓度降低表面负电位,从而减少磷的吸附;当pH<PZC时,提高电解质浓度则降低表面正电位,促进磷的解吸。磷酸根解吸盐效应零点(P_PZSE)值一般都介于土壤或矿物样品吸附磷酸根前后测得的两个PZC值之间。不同浓度电解质溶液中磷解吸量之差与吸附层电位变化量(△ψ_x)呈正相关。     

Nifedipine influence on calcium and aluminum absorption in roots of three sorghum cultivars

A 1,4‐dihydroxypyridine type of ion channel blocker, nifedipine [1,4‐dihydro‐2,6‐dimethyl‐4‐(2‐nitrophenyl)‐3,5‐pyridinedicarboxylate dimethyl ester], was tested on the root absorption of Al³⁺ and Ca²⁺ by sorghum [Sorghum bicolor (L.) Moench] cultivars with varying acid stress tolerance. In an acid stress sensitive cultivar, Funk G522DR, nifedipine (1 μM) influenced Ca²⁺ but not Al³⁺ absorption. In one acid stress tolerant cultivar, SC574, nifedipine (1 μM) influenced both Ca²⁺ and Al³⁺ absorption. In a second acid stress tolerant cultivar, SC283, nifedipine (1 μM) did not influence Ca²⁺ but did influence Al³⁺ absorption. Considerable genetic diversity is present in Ca²⁺ and Al³⁺ absorption between sorghum cultivars.     

Reactions of nucleic acid bases with inorganic soil constituents

The adsorption at pH's 4, 6 and 8 of adenine, guanine, cytosine, thymine and uracil on clays (montmorillonite, illite and kaolinite), Fe- and Al-oxides (goethite, hematite and gibbsite), a soil, and on a laboratory-prepared fulvic acid-montmorillonite complex was investigated. Portions of the clays and soil were saturated with H⁺, Fe³⁺ and Ca²⁺.Quantitatively, the extent of adsorption of nucleic acid bases by the clays was proportional to their exchange capacities, but the nature of the dominant cation had only minor effects. By contrast, the adsorption was strongly affected by pH, tending to decrease with increase in pH. Adsorption on goethite and gibbsite was lower than that on clays, while adsorption of nucleic acid bases on soils was slightly lower than that on oxides. The fulvic acid-montmorillonite complex adsorbed substantial, although smaller amounts of purines and pyrimidines, than did montmorillonite alone. The main adsorption mechanism at pH 4 appeared to be cation exchange whereas at pH 8 complex formation between the nucleic acid bases and cations on inorganic surfaces seemed to occur.The results of this and earlier work show that both inorganic and organic soil constituents adsorb nucleic acid bases. Which adsorption reaction predominates will depend on the clay and organic matter content and on the pH.     

Cation activation of pyrophosphatases from soil microorganisms

The intracellular inorganic pyrophosphatases obtained from mixed cultures of soil microorganisms were characterised in terms of the activating cation and pH-activity profile. Microorganisms were grown in an initial culture 10 mm in tetrasodium pyrophosphate, a nutritionally non-specific aqueous medium, buffered at pH 7.0 with an organic buffer and inoculated with soil. The intracellular pyrophosphatases in a desalted, cell-free enzyme preparation were examined for activity in assays using 1 mM tetrasodium pyrophosphate and nine cations (Mg²⁺, Zn²⁺, Co²⁺, Mn²⁺, Fe²⁺, Ca²⁺, Cu²⁺, Al³⁺ and Fe³⁺) over the pH range 2–10, with appropriate buffers. Only the first 5 cations activated the enzymes. The pH-activity profiles for each cation were different and each displayed only one pH optimum. The pH optima were not greatly affected by cation concentration or kind of buffer. The specific activities at the optimum pH and cation concentration for each culture decreased in order Mg²⁺ > Zn²⁺ > Co²⁺ > Mn²⁺ > Fe²⁺. The results indicate the production of functionally similar enzymes by diverse microorganisms.     

Interactions between montmorillonite and fulvic acid

The isotherms at 20°C for the adsorption of ¹⁴C-labelled fulvic acid from aqueous solutions by montmorillonite containing different exchangeable cations, have been determined. Below a concentration of 0.45 mg/ml and at near neutral pH, all samples give linear isotherms, the slope of which increases in the order Ba²⁺ < Ca²⁺ < Zn²⁺ < La³⁺ < Al³⁺ <Cu²⁺ < Fe³⁺. In the absence of interlayer expansion, the shape of the isotherms is interpreted in terms of solute entry into intercrystalline pores within a clay domain. The affinity of fulvic acid for the clay surface is related to the ionic potential or polarising power of the exchangeable cation. It is inferred that fulvic acid adsorbs by hydrogen bonding between an anionic group of the acid and a water molecule in the primary hydration shell of the saturating cation. Comparison of the data with those for the humic acid extracted from the same organic matter source, indicates that secondary interactions between adsorbed molecules or directly with the montmorillonite surface, contribute to the overall affinity. With samples saturated with Al³⁺, Fe³⁺, and Cu²⁺ ions, part of the adsorbed fulvic acid may also be attached to the clay by a complexation reaction involving the metals as such, or when they exist as polyhydroxy compounds at the mineral surface.     

Lupin and pea differ in root cell wall buffering capacity and fractionation of apoplastic calcium

Lupin (Lupinus angustifolius L.) and pea (Pisum sativum L.) differ substantially in their root growth at pH≥6. The mechanisms underlying such a variation are not fully understood. The H⁺ buffering capacity of isolated cell wall and calcium binding property of intact roots of these two species were compared under various experimental conditions. The shape of the H⁺/OH^‐ titration curves of cell wall for lupin and pea showed no major discrepancy except with differed magnitudes. There appeared to be two H⁺‐titratable groups in root cell wall of both species—below pH 6 and above 8. The wall H⁺ buffering capacity of pea roots was lower at pH 4–5, but was greater at pH above 5.5 than that of lupin roots. The fractionation of apoplastic calcium demonstrated that the proportion of easily exchangeable Ca²⁺ was greater while that of tightly bound Ca²⁺ was smaller in pea roots than in lupin roots. In addition, Ca²⁺ in cell wall was more easily exchanged by H⁺ in pea than in lupin roots. The results suggest that the different sensitivity in root growth at pH≥6 of lupin and pea is related to the difference in H⁺ buffering and Ca²⁺ exchange capacities in the root apoplast of these species, and that the greater sensitivity of lupin roots to pH≥6 is partly due to a higher threshold of H⁺ concentration required for cell wall loosening.     

Influence of surface‐applied poultry manure on topsoil and subsoil acidity and salinity: A leaching column study

It has been suggested that surface applications of animal manure can ameliorate both top and subsoil acidity. For that reason, the effects of surface incorporation (0–5 cm) of a high rate of poultry manure to an acid soil on pH and exchangeable and soluble Al in the top‐ and subsoil were investigated in a leaching column study. During the experimental period of 108 d, columns received a total of 875 mm with leaching events occurring after 9, 37, 58, and 86 d. Incorporation of poultry manure into the surface 5 cm resulted in a large rise in pH measured in both 1M KCl and in soil solution. This liming effect was attributed primarily to the substantial CaCO₃ content of poultry manure. In the 15–45 cm layer, pH_KCl was not significantly different between poultry manure and control treatments but surprisingly, soil‐solution pH was substantially less in the poultry‐manure treatments. Exchangeable Al was significantly less in poultry manure than in control in all soil layers although the effect was most marked in the 0–5 cm layer. However, although concentrations and activities of monomeric Al (Al_mono), and the proportion of total Al present as Al_mono, in soil solution were lower under poultry manure than in control in the 0–5 cm layer, the reverse was, in fact, the case in lower soil horizons. This was attributed to a soluble‐salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al³⁺ and H⁺ back into soil solution. Indeed, electrical conductivity and concentrations of Ca²⁺, Mg²⁺_, K⁺, and Na⁺ in soil solution were substantially higher in the poultry‐manure than in the control treatments at all soil depths. Poultry‐manure applications also resulted in substantial increases in the concentrations of Ca²⁺_, Mg²⁺_, K⁺, Na⁺, Al_mono, NH , and NO in leachates, particularly at the fourth leaching. It was concluded that although surface application of poultry manure can raise soil pH in the topsoil, increases in soluble‐salt concentrations in soil solution can greatly modify this effect in the subsoil.     

Research on the Threshold of Aluminum Toxicity and the Alleviation Effects of Exogenous Calcium,Phosphorus, and Nitrogen on the Growth of Chinese Fir Seedlings under Aluminum Stress

Chinese fir (Cunninghamia Lanceolata Lamb, Hook) is generally considered a superior timber in southern China and other areas in the world. In the past few decades, aluminum (Al) toxicity has become one of biggest stress factors in the production and growth of Chinese fir, although this species prefers an acidic environment. To date, the selection of indicator species for Al toxicity remains critical in the field, and Al toxicity has not been successfully treated by artificially controlling Chinese fir plantations. To assess the Al toxicity risk, the height of the dominant tree, the concentration of calcium (Ca²⁺)/Al³⁺ in soil solution, and the concentration of Ca²⁺?/?[Ca²⁺ + iron (Fe³⁺) + Al³⁺] in litter leached organic acids were introduced. The results indicated that eight plots had suffered Al toxicity. The threshold of Al toxicity was 37.53 mg kg^?1 in soil or 1.39 mmol L^?1 in soil solution, a pH of 4.15, a Ca²⁺?/?(Ca²⁺ + Fe³⁺ + Al³⁺) molar ratio of 0.487, and a Ca²⁺/Al³⁺ molar ratio of 1.599. The positive effects of exogenous nutrition (Ca, phosphorus [P], and nitrogen [N]) on the growth of Cunninghamia lanceolata seedlings was also studied in pot experiments based on results in the field. The cation nutrition can lead to detoxification, and the exogenous nutrition thresholds were Ca²⁺/?Al³⁺ ≥ 2.8, phosphorus (P)/?Al³⁺ ≥ 4.4, ammonium (NH₄ ^?)–nitrogen (N)?/?Al³⁺ ≥ 4.5. The data presented in this study are very helpful for the understanding of the degree of Al toxicity and have notable significance for the management of Chinese fir plantations.     

STRUCTURE FORMATION UPON MIXING Na-MONTMORILLONITE WITH BI- AND TRIVALENT ION-CLAYS1

The light transmittance of montmorillonite suspensions saturated with Na⁺, Mg⁺⁺, Ca⁺⁺, Al⁺⁺⁺, Fe⁺⁺⁺ or La⁺⁺⁺ and with known mixtures of these ions was investigated. Also, the kinetics of bi- and trivalent ion montmorillonite tactoid formation and breakdown was followed by recording changes in light transmission as a function of time when M-montmorillonite suspensions (M = Mg⁺⁺, Ca⁺⁺, Al⁺⁺⁺, Pe⁺⁺⁺ or La⁺⁺⁺) were added to Na-montmorillonite suspensions of the same concentration in a titrating vessel placed in the light path of a spectrophotometer. Introduction of a small fraction of Na⁺ onto the exchange complex of M-clay had no effect on the size of the M-tactoids. The breakdown of Mg⁺⁺ and Ca⁺⁺ tactoids occurred as the equivalent fraction of adsorbed Na⁺ increased from 0.2 to 0.5, with mixed Na-M montmorillonite particles having an equivalent fraction of adsorbed Mg⁺⁺and Ca⁺⁺ less than 0.3 remaining as single platelets. Conversely, introducing even a small fraction (<10%) of trivalent onto the exchange complex of Na-montmorillonite caused the formation of tactoids. Instantaneous formation of an intermediate unstable structure occurred upon mixing Na-montmorillonite with M-montmorillonite. It is proposed that edge-to-face association stabilizes this intermediate structure, whereas face-to-face association stabilizes the eventual tactoids.     

Nutrient balance in Scots pine (Pinus sylvestris L.) forest. 2. Effects of plant growth and N-deposition on soil solution and leachate chemistry in a lysimeter experiment

Three years of N application to a Cambic arenosol (Typic Udorthent) in two lysimeter series, one with and one without young saplings of Pinus sylvestris L. have produced significant changes in soil solution and leachate chemistry. An application of 30 kg N/ha^*yr^?1 significantly increased NO₃ ^? leaching from the soil. This N load was also sufficient to significantly increase the mobility of the phyto-toxic elements Al³⁺ and Mn²⁺, likewise to increase leaching of the important plant nutrients Ca²⁺, Mg²⁺ and K⁺. At a N load of 90 kg N/ha^*yr^?1 significant increase in NH₄ ⁺ leaching was observed, but total leaching of NH₄ ⁺ was still very low compared to NO₃ ^? leaching. No significant treatment effects were found for SO₄ ^2?, Fe²⁺ and Cl^? in the leachate. Trees grown in the lysimeters buffered the acidifying effect of N application and increased the leachate pH by 0.2 pH units compared to lysimeters without trees.     

Soil Solution as Affected by Plant Residues and Nitrogen Rates

Cation mobility in acidic soils with low organic‐matter contents depends not only on sorption intensity but also on the solubility of the species present in soil solution. In general, the following leaching gradient is observed: potassium (K⁺) > magnesium (Mg²⁺) > calcium (Ca²⁺) > aluminum (Al³⁺). To minimize nutrient losses and ameliorate the subsoil, soil solution must be changed, favoring higher mobility of M²⁺ (metal ions) forms. This would be theoretically possible if plant residues were kept on the soil surface. An experiment was conducted in pots containing a Distroferric Red Latosol, with soil solution extractors installed at two depths. Pearl millet, black oat, and oilseed radish residues were laid on the soil surface, and nitrogen (as ammonium nitrate) was applied at rates ranging from 0 to 150 mg kg^?1. Corn was grown for 52 days. Except for K⁺ and ammonium (NH₄ ⁺), nitrogen rates and plant residues had little effect upon the concentrations and forms of the elements in the soil solution. Presence of cover crop residues on soil surface decreased the effect of nitrogen fertilizer on Ca leaching. More than 90% of the Ca²⁺, Mg²⁺, and K⁺ were found as free ions. The Al³⁺ was almost totally complexed as Al(OH₃)⁰. Nitrogen application increased the concentrations of almost all the ions in soil solution, including Al³⁺, although there was no modification in the leaching gradient.     

Interactions of allophane with humic acid and cations

Allophanic soils are known to accumulate organic matter, but the underlying mechanism is not well understood. Here we have investigated the sorption of humic acid (HA) by an allophanic clay in the presence of varied concentrations of either CaCl₂ or NaCl as background electrolytes. Both the HA and the clay were separated from New Zealand soils. Much more HA was sorbed in CaCl₂ than in NaCl of the same ionic strength. Apparently Ca²⁺ ions were more effective than Na⁺ ions in screening the negative charge on HA. In CaCl₂ the HA molecule might also assume a more compact configuration than in NaCl. In the presence of CaCl₂ sorption increased, reached a maximum, and then declined as the concentration of HA in solution was increased. This behaviour was not observed in NaCl where sorption showed a gradual and steady increase with HA concentration. We propose that ligand exchange occurs between the surface hydroxyl groups of allophane and the carboxylate groups of HA. As a result, the allophane–HA complex acquires negative charges, requiring the co‐sorption of extraneous cations (Ca²⁺ or Na⁺) for charge balance. The Ca²⁺ co‐sorbed can attract more HA to the complex possibly by a cation‐bridging mechanism, giving rise to a maximum in sorption. The decline in sorption beyond the maximum may be ascribed to a decrease in the concentration of free Ca²⁺ ions through binding to HA molecules in solution. The increase in supernatant pH may be attributed to a ligand exchange reaction between the surface hydroxyls of allophane and the carboxylate groups of HA, and proton binding to the allophane–HA complex.     

Yield,Nutrient Uptake,and Soil Chemical Properties as Influenced by Liming and Boron Application in Common Bean in a No‐Tillage System

Abstract

In Oxisols, acidity is the principal limiting factor for crop production. In recent years, because of intensive cropping on these soils, deficiency of micronutrients is increasing. A field experiment was conducted on an Oxisol during three consecutive years to assess the response of common bean (Phaseolus vulgaris L.) under a no‐tillage system to varying rates of lime (0, 12, and 24 Mg ha^?1) and boron (0, 2, 4, 8, 12, 16, and 24 kg ha^?1) application. Both time and boron (B) were applied as broadcast and incorporated into the soil at the beginning of the study. Changes in selected soil chemical properties in the soil profile (0- to 10‐ and 10- to 20‐cm depths) with liming were also determined. During all three years, gain yields increased significantly with the application of lime. However, B application significantly increased common bean yield in only the first crop. Only lime application significantly affected the soil chemical properties [pH; calcium (Ca²⁺); magnesium (Mg²⁺); hydrogen (H⁺)+ aluminum (Al³⁺); base saturation; acidity saturation; cation exchange capacity (CEC); percent saturation of Ca²⁺, Mg²⁺, and potassium (K⁺); and ratios of exchangeable Ca/Mg, Ca/K, and Mg/K] at both soil depths (0–10 cm and 10–20 cm). A positive significant association was observed between grain yield and soil chemical properties. Averaged across two depths and three crops, common bean produced maximum grain yield at soil pH_w of 6.7, exchangeable (cmol_c kg^?1) of Ca²⁺ 4.9, Mg²⁺ 2.2, H⁺+Al³⁺ 2.6, acidity saturation of 27.6%, CEC of 4.1 cmol_c kg^?1, base saturation of 72%, Ca saturation of 53.2%, Mg saturation of 17.6%, K saturation of 2.7%, Ca/Mg ratio of 2.8, Ca/K ratio of 25.7, and Mg/K ratio of 8.6. Soil organic matter did not change significantly with addition of lime.     

Assessing the relative effects of hydrogen and aluminum ions on primary root growth of white clover seedlings

White clover (Trifolium repens L., cultivar Huia), a dominant forage legume in Appalachia, usually grows poorly on acidic soils common to the region. The effects of bulk solution concentrations of calcium (Ca), hydrogen (H), and aluminum (Al) on the relative root growth (RRG) of white clover were determined using one‐ to three‐day‐old seedlings to assess the relative toxicity of H⁺ and Al. The RRG was affected by bulk solution concentrations of Ca, Al, and pH, in a manner indicative of significant interactions among these parameters. The RRG was directly related to the activities of Al³⁺ or H⁺ at the surface of the root as calculated by the Gouy‐Chapman‐Stern model. Fifty percent inhibition of RRG occurred at activities of 5 and 200 μM Al³⁺ and H⁺, respectively. A large part of the interaction between bulk solution concentrations of Ca, Al, and H could be explained by how these parameters affected the activities of these ions at the root surface.