The liming effect of five organic manures when incubated with an acid soil

A laboratory incubation experiment of 6 months duration was carried out to investigate the liming effects of five organic manures (poultry, pig, and cattle manure, soybean residues, and sewage sludge) when added to an acid soil at a rate of 10 mg g^–1. Soils were sampled after 1, 7, 13, 19, and 25 weeks of incubation. For the animal manures and sewage sludge, soil pH was highest after 1 week incubation and it declined thereafter. However, for soybean residues, pH increased over the first 7 weeks of incubation after which it declined. The decreases in pH were accompanied by accumulation of NO ‐N in the soil. The addition of organic residues to the soil resulted in decreases in the concentrations of exchangeable Al and in both total (Al_t) and monomeric (Al_mono) Al present in the soil solution. The effect was most marked for poultry manure, least marked for cattle manure, and more evident after 7 than 25 weeks incubation. Concentrations of soluble C in the soil solution were elevated in manure‐amended soils. Manure additions resulted in a decrease in the percentage of Al_t present in solution as Al_mono, and this was attributed to complexation of Al by soluble organic matter originating from the manures. It was concluded that organic wastes can act as liming materials when added to acid soils and that the resulting increase in pH and decrease in Al_mono concentrations might provide a window of opportunity for establishment and early growth of crop plants.     

Increases in pH and soluble salts influence the effect that additions of organic residues have on concentrations of exchangeable and soil solution aluminium

It has been suggested that additions of organic residues to acid soils can ameliorate Al toxicity. For this reason the effects of additions of four organic residues to an acid soil on pH and exchangeable and soil solution Al were investigated. The residues were grass, household compost, filter cake (a waste product from sugar mills) and poultry manure, and they were added at rates equivalent to 10 and 20 t ha^?1. Additions of residues increased soil pH measured in KCl (pH_(KCl)) and decreased exchangeable Al³⁺ in the order poultry manure > filter cake > household compost > grass. The mechanism responsible for the increase in pH differed for the different residues. Poultry manure treatment resulted in lower soil pH measured in water (pH_(water)) and larger concentrations of total (Al_T) and monomeric (Al_mono) Al in soil solution than did filter cake. 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. The considerably larger concentrations of soluble C in soil solution originating from the poultry manure may also have maintained greater concentrations of Al in soluble complexed form. There was a significant negative correlation (r = ?0.94) between pH_(KCl) and exchangeable Al. Concentrations of Al_T and Al_mono in soil solution were not closely related with pH or exchangeable Al. The results suggest that although additions of organic residues can increase soil pH and decrease Al solubility, increases in soluble salt and soluble C concentrations in soil solution can substantially modify these effects.     

Biogeochemistry of aluminum in a forest catchment in the Czech Republic impacted by atmospheric inputs of strong acids

The Lysina catchment in the Czech Republic was studied to investigate the biogeochemical response of Al to high loadings of acidic deposition. The catchment supports Norway spruce plantations and is underlain by granite and podzolic soil. Atmospheric deposition to the site was characterized by high H⁺ and SO₄ ^2– fluxes in throughfall. The volume-weighted average concentration of total Al (Al_t) was 28 mol L^–1 in the O horizon soil solution. About 50% of Al_t in the O horizon was in the form of potentially-toxic inorganic monomeric Al (Al_i). In the E horizon, Al_t increased to 71 mol L^–1, and Al_i comprised 80% of Al_t. The concentration of Al_t (120 mol L^–1) and the fraction of Al_i (85%) increased in the lower mineral soil due to increases in Al_i and decreases in organic monomeric Al (Al_o). Shallow ground water was less acidic and had lower Al_t concentration (29 mol L^–1). The volume-weighted average concentration of Al_t was extremely high in stream water (60 mol L^–1) with Al_i accounting for about 60% of Al_t. The major species of Al_i in stream water were fluorocomplexes (Al-F) and aquo Al³⁺. Soil solutions in the root zone were undersaturated with respect to all Al-bearing mineral phases. However, stream water exhibited Al_i concentrations close to solubility with jurbanite. Acidic waters and elevated Al concentrations reflected the limited supply of basic cations on the soil exchange complex and slow weathering, which was unable to neutralize atmospheric inputs of strong acids.     

Solution chemistry in acid forest soils: Are the BC : Al ratios as critical as expected in Switzerland?

The molar ratio of base nutrient cations to total dissolved aluminum (BC : Al_tot) in the soil solution was measured at six forest sites in Switzerland in acid mineral soils to determine whether the ratio measured in the field was lower than the critical value of 1, as predicted by the mapping of exceedances of critical loads of acidity. The soil chemistry was then related to the soil solution composition to characterize the typical effective base saturation (BS) and BC : Al ratio in soil leading to critical BC : Al_tot in the soil solution. The median BC : Al_tot ratio in the soil solution never reached the critical value in the root zone at any sites for the whole observation period (1999–2002), suggesting that the BC : Al_tot ratios measured in the field might be higher than those modeled for the determination of critical loads of acidity. The gibbsite model usually applied for the calculation of critical loads was a poor predictor of the Al³⁺ activity at the study sites. A curvilinear pH‐pAl³⁺ relationship was found over the whole range of pH (3.8–6.5). Above a pH of 5.5, the slope of the pH‐pAl³⁺ relation was close to 3, suggesting equilibrium with Al(OH)₃. It decreased to values smaller than 1.3 below a pH of 5.5, indicating complexation reactions with soil organic matter. The BS and the BC : Al ratios in the soils were significantly correlated to the BC : Al_tot ratios in the soil solution. The soil solutions with the lowest BC : Al_tot ratios (≤ 2) were typically found in mineral soils with a BS below 10 % and a BC : Al ratio in the soil lower than 0.2. In acid pseudogleyed horizons overlying a calcareous substrate, the soil solution chemistry was strongly influenced by the composition of the underlying soil layers. The soil solutions at 80 cm had pH values and BC : Al_tot ratios much higher than expected. This situation should be taken into account for the calculations of critical loads of acidity.     

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.     

Effects of pretreatment and solution chemistry on solubility of rice‐straw phytoliths

Rice is a Si‐accumulator plant, whereby Si has physio‐chemical functions for plant growth. Its straw contains high shares of plant silica bodies, so‐called phytoliths, and can, when returned to the soil, be an important Si fertilizer. Release of Si from phytoliths into soil solution depends on many factors. In order to improve prognosis of availability and management of Si located in phytoliths, in this study we analyzed the effect of pretreatment of rice straw by dry and wet ashing and the soil‐solution composition on Si release. Dry ashing of rice straw was performed at 400°C, 600°C, and 800°C and wet ashing of the original straw and the sample from 400°C treatment with H₂O₂. To identify the impact of soil‐solution chemistry, Si release was measured on separated phytoliths in batch experiments at pH 2–10 and in presence of different cations (Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺) and anions (Cl^–, NO$ _3^- $ , SO$ _4^{2-} $ , acetate, oxalate, citrate) in the concentration range from 0.1 to 10 mmol_c L^–1. After burning rice straw at 400°C, phytoliths and biochar were major compounds in the ash. At an electrolyte background of 0.01 mol_c L^–1, Si released at pH 6.5 was one order of magnitude higher than at pH 3, where the zeta potential (ζ) was close to zero. Higher ionic strength tended to suppress Si release. The presence of cations increased ζ, indicating the neutralization of deprotonated Si‐O^– sites. Monovalent cations suppressed Si release more strongly than bivalent ones. Neutralization of deprotonated Si‐O^– sites by cations might accelerate polymerization, leading to smaller Si release in comparison with absences of electrolytes. Addition of Al³⁺ resulted in charge reversal, indicating a very strong adsorption of Al³⁺, and it is likely that Si‐O‐Al‐O‐Si bonds are formed which decrease Si release. The negative effect of anions on Si release in comparison with deionized H₂O might be due to an increase in ionic strength. The effect was more pronounced for organic anions than for inorganic ones. Burning of rice straw at low temperatures (e.g., 400°C) appears suitable to provide silicon for rice in short term for the next growing season. High inputs of electrolytes with irrigation water and low pH with concomitant increase of Al³⁺ in soil solution should be avoided in order to keep dissolution rate of phytoliths at an appropriate level.     

Effects of phosphogypsum or calcium sulfate on aluminon reactive aluminum in solutions at varying pH

Abstract

Growing evidence of positive crop responses to gypsum or phosphogypsum (PG) application in acid soils strongly support the use of these amendments as an ameliorant of subsoil acidity. Although gypsum improves Ca availability in subsoils, its role in alleviation of Al toxicity needs careful attention. In the current study, either PG, CaSO₄.2H₂O or CaCl₂.2H₂O was added (to supply 12 mM Ca) to solutions containing 40 μM Al at pH 4.1 + 0.1. Solution pH was gradually raised to 4.5, 4.8 and then to 5.3 at various time intervals during 25 d aging of the solutions at 25 + 1^OC.

Concentration of Al measured by aluminon method without preacidification and preheating, referred to as “reactive Al”; in this paper, was 16 μM in 2 g L^‐1PG solution without added Al. This accounted 38% of total soluble Al in PG solution. Addition of 2 g L^‐1PG to solution containing 40 μM Al, resulted in only 42% of total Al in solution present in forms reactive with aluminon. According to MINTEQ speciation model, Al in solution was present as an entirely complexed form with F^‐. An increase in solution pH up to 5.3 had no effect on measured concentration of reactive Al or predicted distribution of Al species.

Addition of CaSO₄.2H₂O to 40 μMAl solutions had no effect on the concentration of reactive Al within pH 4.1 ‐4.8, however, up to 62% of total Al was in a form complexed with SO₄ ^2‐, as predicted by MINTEQ model. The concentration of reactive Al decreased by 60% at pH 5.3. Addition of CaCl₂.2H₂O also had no effect on the concentration of reactive Al within pH 4.1 ‐ 4.8. Nearly 73 ‐ 94% of total Al was present in Al³⁺form. An increase in pH to 5.3, decreased the concentration of reactive Al by 27%. The results suggest that ion‐pairing of Al with F^‐would appear to be a possible mechanism for alleviation of Al toxicity by PG at pH range 4.1 ‐ 5.3. With regard to CaSO₄.2H₂O, at pH 4.1 ‐ 4.8 ion‐pairing with SO.₄ ^2‐appears to be possible mechanism for the alleviation of Al toxicity. In addition, at pH 5.3 a considerable decrease in reactive Al was evident which would further alleviate Al toxicity.     

Forms of soluble aluminium in acidic topsoils estimated by ion chromatography and 8-hydroxyquinoline and their correlation with growth of subterranean clover

Labile Al in the soil solution measured by 8-hydroxyquinoline (Al_HQ) was a better predictor of plant growth than trivalent Al (Al_IC³⁺) measured by ion chromatography (IC). HQ reacted with some organic Al complexes which did not separate during chromatography. In the presence of oxalic acid, Al_HQ was greater than Al_IC³⁺, which was the same as the greater than Al³⁺ (Al³⁺_Calc), whereas in the presence of citric acid, Al_HQ was greater than Al_IC³⁺, and both were greater than Al⁺³_Calc, In extracts of soils that had been acidified, Al³⁺_IC was less than Al_HQ, which was similar to Al³⁺_Calc, when it was assumed that the only complexing ligands were OH^? and F^?. The proportion of Al³⁺_IC in the soil solutions decreased more than Al_HQ as the pH increased. Organic ligands appeared to form complexes with Al at the expense of AIF complexes. Forms of Al detected by IC differed in CaCl₂ extracts and soil solutions. Al_HQ in the CaCl₂ extracts and soil solution were closely correlated, although the proportion of Al_HQ was higher in the CaCl₂ extracts. And soil solutions. Al_HQ in the CaCl₂ extracts and soil solution were closely correlated, although the proportion of Al_HQ was higher in the CaCl₂ extracts.     

Dynamics of aqueous aluminum species in a podzol affected by experimental MgSO4 and (NH4)2SO4 treatments

Chemistry of aqueous Al in a podzol on a Norway spruce (Picea abies [L.] Karst.) site in the Black Forest (SW Germany) and changes induced by experimental applications of MgSO₄ were studied. Soil solution taken from the O, E and BC horizons were analyzed for the fractions ‘labile monomeric Al’, ‘non-labile monomeric Al’, and ‘acid-reactive Al’. The activities of ‘inorganic monomeric Al’ species and the saturation indices (SI) of the soil solution with respect to Al-bearing minerals were calculated using the equilibrium speciation model WATEQF. On the untreated plot, soil leachates are characterized by Al_tot concentrations of 0.1 mg L^?1 (mineral soil). In the O horizon, the fractions ‘acidsoluble Al’ and ‘non-labile monomeric Al’ (mainly organically complexed Al) together comprise 80% of Al_tot. In the leachates from the mineral soil Al³⁺ prevails, being 50% of Al_tot. Al-F-complexes make up 5 to 10% in all horizons. MgSO₄ and (NH₄)₂SO₄ treatments resulted in an intense Al mobilization up to 50 mg L^?1. In this situation, 60% of Al_tot is covered by Al³⁺ and 40% by non-phytotoxic Al-SO₄-complexes. After rainfall events, mobilized Al is quickly translocated into the subsoil, with water flow through macropores then appearing to be an important mechanism. In both treatments, soil solution chemistry was favorable for the precipitation of the Al(OH)SO₄-type minerals alunite and jurbanite. However, a control of Al solubility by this process is not likely due to kinetic restraints. Application of MgSO₄ was followed by an increase of the Mg/Al molar ratio in the soil solution, whereas the Ca/Al ratio decreased. After treatment with (NH₄)₂SO₄ both the Ca/Al and the Mg/Al ratios deteriorated.     

Correcting soil acidity of a highly weathered Ultisol with chicken manure and sewage sludge

Abstract

The seriousness of soil acidity and the unavailability of “conventional”; liming materials in many developing countries necessitate a search for alternatives. With this goal in mind, the liming potential of two organic manures was investigated. The investigation was conducted in the greenhouse, using a highly weathered, acid Ultisol. Application rates were 0, 5, 10, 20, and 40 g kg^‐1 for chicken manure and 20 g kg^‐1 for sewage sludge. Treatments of Ca(OH)₂ at 2, 4, 6, and 8 cmol_ckg^‐1, were included for comparison.

Based on growth response of Desmodium intortum, a tropical forage legume with a relatively high Ca requirement and low Al tolerance, it was demonstrated that soil acidity can be corrected by either Ca(OH)₂ or organic manure additions. Both lime and manures raised soil pH and inactivated Al. In terms of pH increases, 5 and 10 g chicken manure kg^‐1 were equivalent to 3.4 and 6.7 cmol_ckg^‐1; and 20 g sludge kg^‐1, equivalent to 6.5 cmol_ckg^‐1 as Ca(OH)₂. The manures also detoxified soluble Al by organic complexation and enhanced Ca uptake of the Desmodium. The plant's maximum growth required at least 1.0% Ca in leaves, and this growth was reduced by half when leaf Al ≥ 76 mg kg^‐1 and soil‐solution Al³⁺ activity ≥ 4 μM.     

Agronomic Implications of the Application of Lime plus Gypsum By‐products to a Hyperdistric Acrisol from Western Spain

Abstract: A laboratory experiment involving the use of leaching columns reproducing the topmost portion of a Hyperdystric Acrisol (FAO 1998 FAO. 1998. World reference base for soil resources, Rome: FAO, ISRIC, and ISSS. (World Soil Resources Report No. 84) [Google Scholar]) or plinthic Palexerult (Soil Survey Staff 2003 Soil Survey Staff. 2003. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys, Washington, D.C.: U.S. Government Printing Office. (Agriculture Handbook No. 436) [Google Scholar]) treated in its Ap horizon with sugar foam wastes and phosphogypsum was conducted. The amendments increased the contents in exchangeable calcium (Ca) of the Ap horizon and, to a lesser extent, also that of the AB horizon. However, the contents in exchangeable magnesium (Mg) and sodium (Na) decreased as much in Ap as they did in AB; by contrast, the potassium (K) content exhibited a less marked decrease. The potassium chloride (KCl)–extractable aluminium (Al) of the Ap horizon was dramatically decreased much more than that of the AB horizon by the amendments. In the soil solution from Ap, the amendments raised the pH and decreased the Al concentration; in that from AB, however, they caused an initial pH decrease, a tendency that reversed as the gypsum was leached and eventually led to the pH exceeding that in the soil solution from control. The first few water extractions exhibited increased Mg concentration. This trend was reversed in the second leaching cycle, where the concentrations of Mg in the amended columns were lower than those in the controls. In the soil solution, the variation of the Ca and sulphate (SO₄ ^2–) concentrations was influenced by the salt‐sorption effect. The total Al content in soil solution from AB increased during the first leaching cycle and then decreased during the second. The amendments decreased the activities of Al³⁺, AlOH⁺², and Al(OH)₂ ⁺ in the Ap horizon and increased those of Al³⁺, AlSO₄ ⁺, Al(SO₄)₂ ^?, and AlF⁺² in the first leaching cycle in the AB horizon. The productivity of the Ap horizon after the treatments was assessed using a wheat crop (T. aestivum, var. ‘Jabato’) in a greenhouse.     

Aluminium Toxicity Risk for Pinus pinaster in Acid Soils (Galicia,NW Spain)

The influence of bedrock on aluminium toxicity and aluminium speciation in the soil solution was studied in four Pinus pinaster plots. Growth and biomass parameters in the acidic soils were also evaluated in relation to different Al toxicity indices. The plots were developed over slate, biotitic schist, mica schist and granite. Samples of rhizospheric and non‐rhizospheric soil, 1‐year‐old needles and roots were collected in each study plot. Total Al, reactive Al, acid‐soluble Al, non‐labile and labile Al and Al species (Al³⁺, Al‐OH, Al‐F and Al‐SO₄) were determined in soil solution. Reactive Al dominated over the acid‐soluble Al, and the non‐labile Al predominated over the labile Al in all soils, but particularly over mica schist. In the biotitic schist soil, the Al forms and total Al were lower, whereas concentrations were always higher over mica schist. The Al forms considered most toxic were Al³⁺ and Al‐OH, and Al concentrations were highest over slate and mica schist. Al toxicity indices in soil, needle and roots showed a risk of toxicity in mica schist, slate and granite. The stand site indices over slate and mica schist were lower, consistent with the high labile Al and Al³⁺ + Al‐OH in soil solution. Despite the high stand site index over granite, the growth efficiency was low, in accordance with very low ratios of Ca/Al in needles or fine roots. This confirmed the adaptation of maritime pine to granitic substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

Salts and acids as determinants of the solution composition of acidic forest soils — anion effects

The study aimed at evaluating whether salt-induced mobilization of acidity may be modified by the type of anion. For this purpose, the effects of different neutral salts on the solution composition of acid soils were investigated. The results were compared with those of the addition of acids. Two topsoil (E and A) and two subsoil horizons (Bs and Bw) were treated with NaCl, Na₂SO₄, MgCl₂, MgSO₄, HCl, and H₂SO₄ at concentrations ranging from 0 to 10 mmol dm^?3. With increasing inputs of Cl^? the pH of the equilibrium soil solution dropped, the concentrations of Al and Ca increased, and the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios decreased. These effects were the least pronounced when NaCl was added and the most at the HCl treatments. According to the release of acidity, the topsoils were more sensitive for salt-induced soil solution acidification whereas on base of the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios, the salt effect seems to be more important for the subsoils. Addition of S0₄^2? salts and H₂SO₄ induced higher pH and lower Al concentrations than the corresponding Cl^? treatments due to the SO₄^2? sorption, especially in the subsoils. The Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios were higher than those of the corresponding Cl^? treatments. In subsoils even after H₂SO₄ additions these ratios were not higher than those of the NaCl treatments. The results indicate (I) that speculation about the effects of episodic salt concentrations enhancement on soil solution acidification not only need to consider the ionic strength and the cation type but also the anion type, (II) that salt-induced soil solution composition may be more crucial in subsoils than in topsoils, and (III) that in acid soils ongoing input of HNO₃ due to the precipitation load may induce an even more acidic soil solution than the inputs of H₂SO₄ of the last decade.     

第四纪红粘土发育的红壤在施用石灰和石膏后元素的淋溶特征

本文利用模拟土柱试验研究了施用石灰和石膏对第四纪红粘土发育的红壤中元素淋溶过程的影响。结果表明,施用石灰后１０ｃｍ土层中除Ｃａ＾２＋以外的阳离子元素的淋失量减少,而ＳＯ４＾２－和ＨＣＯ３＾－的淋失量增加;施用石膏后１０ｃｍ土层中所有阳离子元素,特别是ＡＩ＾３＋的淋失量增加。红壤中Ｃａ＾２＋的淋失以自由态为主,施用石膏后与ＳＯ４＾２－结合的比例增加,不同处理中３０ｃｍ土层处铝的淋失以自由态为离,１０     

Suitability of the aluminon technique for measuring phytotoxic aluminum in solutions with varying sulfate concentrations

Abstract

Considerable uncertainty prevails concerning a suitable measure that can adequately describe Al phytotoxicity in nutrient and soil solutions. A study was conducted to evaluate the ability of a modified aluminon technique to discriminate between phytotoxic and non‐phytotoxic Al in solutions containing 80 μM Al with varying levels of CaSO₄(625 to 10000 μM), at two pH levels (4.2 and 4.8). The concentration of Al measured by the modified aluminon technique ranged from 18.3 to 77.7 μM,thereby indicating substantial polymerization in some of the solutions. The greatest amount of polymerization occurred at pH 4.8 in the presence of 625 μM CaSO₄. Increasing additions of CaSO₄resulted in an increase in predicted activity of AlSO₄ ⁺at both pH levels. However, with increasing addition of CaSO₄, the predicted activity of Al³⁺decreased at pH 4.2 or remained relatively constant at pH 4.8. The relationship between the sum of predicted activities of monomeric Al (Sa_{Al mono.}) in solution and tap root length of soybean [Glvcine max(L.) Merr.] cv. Lee was extremely poor, thereby indicating the inability of the modified aluminon technique to measure phytotoxic Al in solutions employed in the current study. This difficulty was due to failure of the modified aluminon technique to exclude lesser phytotoxic AlSO₄ ⁺species. The activity of Al³⁺was closely related to tap root length (R²= 0.865). The prediction of root length response to Al was further improved (R²= 0.899) by considering the solution Al index as: S[3a_A13+ + 2a_Al(OH)2+ + a_A1(OH)+]. There was a poor relationship between tap root length and the concentration of polymeric Al, thus suggesting the lower phytotoxicity of this component under the prevailing solution conditions.     

Speciation and mobilization of aluminium and cadmium in podzols and cambisols of S. Sweden

Processes governing the mobilization of Al and Cd in podzols and cambisols of S. Sweden having different tree layer vegetation (Picea abies, Fagus sylvatica, or Betula pendula) were investigated. Speciation of Al and Cd in soil solutions were performed by a column cation exchange procedure (cf. Driscoll, 1984) in combination with thermodynamic calculations. Podzols in spruce and beech stands were characterized by a high release of organic compounds from the O/Ah horizons, resulting in a high organic complexation of Al (c. 93%) in the soil solution from the E horizon (15 cm lysimeters). Organic complexes were mainly adsorbed/precipitated in the upper Bh horizon and the overall transport of Al at 50 cm depth was governed by a pH dependent dissolution of a solid-phase Al pool. In the cambisols, inorganic Al forms were predominant at both 15 and 50 cm depth, and Al solubility was closely related to solution pH. Secondary minerals like synthetic gibbsite, jurbanite, kaolinite or imogolite could generally not explain measured solution Al³⁺ activities. Results instead indicated that the relatively large organically bound solid-phase Al pools present in both soil types could do so. The column fractionation procedure could be used only qualitatively for Cd, but results strongly indicated that Cd-organo complexes contributed significantly to the overall mobilization of Cd in the podzol E horizons. In all other soil solutions, Cd²⁺ was the predominant species. Both solid-phase and solution chemistry suggests that ion exchange processes controlled the Cd²⁺ activities in these solutions. All reactive solidphase Cd was extractable by NH₄Cl and Cd²⁺ activities could in most cases effectively be modeled by the use of ion exchange equations. Solubilized Al³⁺ efficiently competed for exchange sites and played an important role for the Cd mobilization in these soils.     

Simulated effects of acid deposition on podzolic soils: Consequences of process and parameter aggregation

Solution cation concentrations and base cation leaching were simulated for a homogenous soil block and a soil showing five horizons of a podzolic forest soil. The dynamic model ACIDIC simulated water flow, nutrient uptake for tree growth, and cation exchange between H⁺, Al³⁺, Ca²⁺, Mg²⁺ and K⁺ in forest soil. In the multi-layer simulations exchangeable base cation concentrations changed most in the O horizon. The subsoil had a decisive effect on the pH of the runoff and base cation leaching from the soil. The one-layer model underestimated Ca and Mg leaching and overestimated H⁺ and Al concentrations in the runoff. In the eluvial and the top of illuvial horizon the solution Al / (Ca + Mg) ratio exceeded that in one-layer structure more than 10-fold. Cases with the horizon-specific cation exchange coefficient values and mean coefficient values for all layers showed only minor differences in Al / (Ca + Mg) ratio. The vertical variation in the soil chemical properties should be accounted for even if some details of processes and parameters were unavailable.     

Soil base saturation affects root growth of European beech seedlings§

To assess the potential effects of Al toxicity on the roots of young European beech (Fagus sylvatica L.), seeds were sown in soil monoliths taken from the Ah and B horizons of forest soils with very low base saturation (BS) and placed in the greenhouse. The Ah horizons offered a larger supply of exchangeable cation nutrients than the B horizons. After 8 weeks of growth under optimal moisture conditions, the seedlings were further grown for 14 d under drought conditions. Root‐growth dynamics were observed in rhizoboxes containing soils from the Ah and B horizons. The concentrations of Al³⁺, base cations, and nitrate in the soil solution and element concentrations in the root tissue were compared with above‐ and belowground growth parameters and root physiological parameters. There was no strong evidence that seedling roots suffered from high soil‐solution Al³⁺ concentrations. Within the tested range of BS (1.2%–6.5%) our results indicated that root physiological parameters such as O₂ consumption decreased and callose concentration increased in soils with a BS < 3%. In contrast to the B horizons, seedlings in the Ah horizons had higher relative shoot‐growth rates, specific root lengths, and lengths and branching increments, but a lower root‐to‐shoot ratio and root‐branching frequency. In conclusion, these differences in growth patterns were most likely due to differences in nutrient availability and to the drought application and not attributable to differences in Al³⁺ concentrations in the soil solution.     

Soil tests for aluminum toxicity in the presence of organic matter: Laboratory development and assessment

Abstract

Al toxicity in plants is related to the activity of Al³⁺ and Al‐hydroxy monomers in the soil solution, whereas Al complexed with ligands such as fluoride (F), sulphate (SO₄ ^2‐), and oxalate is not toxic. Estimation of toxic Al relies on measurement of “labile”; Al after short contact times with colorimetric reagents or cation‐exchange resins. However, shifts in equilibrium may result in non‐toxic forms of Al reacting with the complexing agent or resin.

A series of laboratory experiments tested the degree to which labile Al is related to Al³⁺ in simplified media and compared methods of estimating labile Al in the presence of organic ligands and in soils. Cation‐exchange resins extracted more than the theoretical concentration of Al³⁺ from solutions containing a range of concentrations of OH^‐ and SO₄ ^2‐. More Al was extracted in 15 s by 8‐hydroxy‐quinoline than by Chelex‐100 from solutions of Al‐humate at pH 4. In sands which had been spiked with Al and organic matter, the estimation of labile Al varied with both the method of measurement and type of extract. The cations present in commonly used soil‐extracting chloride solutions can decrease the proportion of organically complexed Al.     

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO₃ extractable P (Olsen‐P) and determined the changes in soil inorganic P (P_i) and organic P (P_o) caused by a yearly dose of 52 kg P ha^—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean‐wheat system on Vertisol. In general, the contents of Olsen‐P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen‐P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen‐P by 1 mg kg^—1 was 10.5 kg ha^—1 without manure and application of 8 t manure reduced it to 8.3 kg ha^—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO₃‐P_i and P_o) and moderately labile (NaOH‐P_i and P_o) fractions linearly and manure application enhanced accumulation of P_o. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P_t). Excess fertilizer P application in presence of manure led to increased levels of Olsen‐P in both topsoil and subsoil. In accordance, the recovery of P_t from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.