ALLEVIATION OF ALUMINUM IN ACIDIC SOILS AND ITS EFFECT ON GROWTH OF HYBRID AND CLONAL OIL PALM SEEDLINGS

Aluminum (Al) toxicity is an important factor in limiting crop production. The present study examined the Al alleviation effects on the growth of hybrid (breeding) and clonal (tissue culture) of D × P oil palm seedlings. The experiment was performed using calcium carbonate (CaCO₃), and ground magnesium limestone (GML) and magnesium carbonate (MgCO₃) as soil-amendments at different rates in Colombia and Malaysia, respectively. The effects of the treatments were evaluated monthly on vegetative variables and visual symptoms. Chlorophyll concentrations were recorded in Malaysia at the fifth month growing stage. The different amendments improved the soil fertility and it was reflected on better performance of shoot and root growth. The chlorophyll content in the frond number 3 for both materials enhanced significantly when Al saturation was low (0–30%). The results from the experiment revealed the importance of neutralization of Al in reducing its toxicity in oil palm.     

Soybean root growth in relation to ionic composition in magnesium-amended acid subsoils: Implications on root citrate ameliorating aluminum constraints

Abstract

Hydroponic studies with soybean (Glycine max [L.] Merr.) have shown that µmol L^?1 additions of Mg²⁺ were as effective in ameliorating Al rhizotoxicity as additions of Ca²⁺in the mmol L^?1 concentration range. The objectives of this study were to assess the ameliorative effects of Mg on soybean root growth in acidic subsoils and to relate the soil solution ionic compositions to soybean root growth. Roots of soybean cultivar Plant Introduction 416937 extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoils from the Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic) series. The three Mg treatments consisted of native equilibrium soil solution concentrations in each soil (50 or 100 µmol L^?1) and MgCl₂ additions to achieve 150 and 300 µmol L^?1 Mg (Mg150 and Mg300, respectively) in the soil solutions. Root elongations into Mg-treated subsoils were compared with a CaCO₃ treatment limed to achieve a soil pH value of 6. Subsoil root growth responses to the Mg treatments were less than for the lime treatments. Root length relative to the limed treatments for all subsoils (RRL) was poorly related to the activity of the soil solution Al species (Al³⁺ and Al-hydroxyl species) and Mg²⁺. However, the RRL values were more closely related to the parameters associated with soil solution Ca activity, including (Ca²⁺), (Al³⁺)/(Ca²⁺) and (Al³⁺)/([Ca²⁺] + [Mg²⁺]), suggesting that Ca could be a primary factor ameliorating Al and H⁺ rhizotoxicity in these subsoils. Increased tolerance to Al rhizotoxicity of soybean by micromolar Mg additions to hydroponic solutions, inducing citrate secretion from roots to externally complex toxic Al, may be less important in acid subsoils with low native Ca levels.     

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.     

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.     

单宁酸对不同pH茶园土壤中活性铝形态分布的影响

采集云南省普洱市和江西省南昌县两地典型的茶园土壤,通过添加HCl和Ca(OH)2调节土壤pH,研究不同pH(3.0、3.5、4.0、4.5)茶园土壤添加0.4 mmol·kg 1、2.0 mmol·kg 1、4.0 mmol·kg 1、8.0 mmol·kg 1、12.0 mmol·kg 1单宁酸后,活性铝形态交换态铝(Al3+)、单聚体羟基铝[Al(OH)2+、Al(OH)+2]、酸溶无机铝[Al(OH)03]和腐殖酸铝[Al-HA]的分布特征。结果表明:单宁酸添加量为0~0.4 mmol·kg 1和0~2.0 mmol·kg 1时,江西南昌和云南普洱茶园土壤中交换态铝随土壤pH的增加呈明显下降趋势,而羟基态铝、酸溶无机铝和腐殖酸铝呈逐渐上升趋势;当单宁酸浓度增至2.0 mmol·kg 1以上时,随土壤pH的增加,单宁酸对活性铝释放的抑制作用增强,各形态活性铝含量都较低,且不同pH处理土壤间的差异不显著。0~20 cm土层土壤与20~40 cm土层土壤变化规律大致相似,总体上看,下层土壤活性铝总量高于上层。云南普洱茶园土壤活性铝总量明显高于江西南昌的茶园土壤。相关分析表明,0~20 cm土层土壤中,pH与羟基态铝、腐殖酸铝、土壤酸碱缓冲容量(pHBC)呈正相关(r=0.796,P0.01;r=0.960,P0.01;r=0.852,P0.01);pHBC与交换态铝、羟基态铝呈负相关(r=0.904,P0.01;r=0.645,P0.05),而与腐殖酸铝呈正相关(r=0.795,P0.01)。同时,单宁酸加入浓度为0~0.4 mmol·kg 1时,土壤pH明显上升,之后随着单宁酸加入浓度的增加土壤pH持续下降,土壤pH(YpH)与单宁浓度(CDN)在此阶段基本符合方程:YpH=0.04CDN+3.82(R2=0.95,P0.01)的线性变化趋势,在单宁酸浓度达到8.0~12.0 mmol·kg 1时,土壤pH基本不再变化。     

Effects of Alum-treated Waste Water Sludge on Barley Growth

Alum sludge derived from a municipal wastewater plant was used as a soil amendment in a greenhouse study with barley (Hordeum vulgare) as the test crop. Treatment variables included the soil pH (4.5, 5.1 and 6.5), the amount of Al in the sludge (control = 30 mg Al_T/g; alum sludges = 38 and 52 mg Al_T/g), and the sludge application rate (100 and 270 kg N_T/ha). Soil amendment with the two alum sludges reduced soil pH, increased Al³⁺ activity in the soil solution, and reduced barley growth over the 6-week experiment. Barley growth decreased as the Al³⁺ activity in the sludged soil solution increased, but for a given Al³⁺ the phytotoxicity of Al was markedly pH dependent. For example, at a pH of 5.0 ± 0.1 an Al³⁺ activity of 0.5 μM was sufficient to inhibit plant growth by about 50% this IC₅₀ value increased five-fold to about 2.5 μM when the soil pH was 4.5 ± 0.1. This decrease in the toxicity of Al50 with acidification was explained in terms of a competitive interaction between the H⁺-ion and Al³⁺ at the root surface. Stepwise multiple regression allowed the prediction of aerial leaf biomass from soil pH and sludge application rate.     

Hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions

Soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation under varying concentrations of solution hydrogen (H) and aluminum (Al) was investigated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment with solutions adjusted to either different pH values from 3.7 to 5.5 or a factorial combination of pH (4.0,4.6, and 5.2) and Al (0,7.5, 15, and 30 μM) levels. Ionic forms of Al were estimated with GEOCHEM and solution Al was determined with ferron. Boron (B) (18.5 μM) and zinc (Zn) (0.5 μM) were supplied to all solution treatments, in addition to 2000 μM Ca, after preliminary studies at pH 5.2 without Al indicated that their omission inhibited length of tap roots and their laterals in the subsurface compartment. Both H⁺ and Al inhibited the length of lateral roots more than tap roots. Lateral roots failed to develop on tap roots at pH<4.3 or in treatments with 30 μM Al. Relative tap root length (RRL) among treatments receiving Al correlated with Al as measured by reaction with ferron for 30s. Ferron‐reactive Al was correlated to GEOCHEM‐predicted Al³⁺ activity (r=0.99). A 50% reduction in RRL occurred with either 2.1 μM Al³⁺ activity or 4.9 uM ferron‐reactive Al. The absence of shoot and soil‐root biomass differences among solution treatments in the split‐root system indicated that differences in root growth in the subsurface compartment were not directly confounded with differences in top growth.     

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.     

Effects of soil acidity on the growth of sericea lespedeza

Field experiments were conducted in 1992 and 1993 to examine effects of soil acidity on growth and N₂ fixation by “Serala”; sericea lespedeza [Lespedeza juncea (L.F.) var. sericea (Mig.)]. Effects of acidified soil on N₂ fixation could not be determined because nodulation was suppressed, apparently by sufficient availability of N. Apparently‐suppressive, mean 1993 levels of KCl‐extractable NH₄ and NO₃ in zero nitrogen (N) control treatments were 20 and 13 mg‐kg^‐1, respectively. In soil acidified with sulfur (S), growth of sericiea lespedeza was significantly reduced (PO.05) when the concentration of water‐extractable Mn exceeded 1.3 mM or calculated Mn²⁺ activity exceeded 0.4 mM. This occurred at pH values of 4.1 to 4.3 depending on S treatment. At a given value of pH, shoot dry weight production was greater in S‐amended soil than in Al₂SO₄‐amended soil. Reduced growth in the latter did not appear to be directly related to higher measured levels of toxic Al but may have been caused by a combination of aluminum (Al), hydrogen (H), manganese (Mn), and phosphorus (P) effects. Lespedeza growth was lowest in nonacidified soil with pH values near 6.0, indicating a preference for acid soils by the variety “Serala.”; The demonstrated tolerance of sericea lespedeza to acid soils make it a valuable reclamation species. However, Mn may inhibit growth in acidic soils when the activity of water‐extractable Mn²⁺ exceeds 0.4 mM, and it may not fix appreciable N₂ unless available soil N is quite low.     

A Scanning Electron Microscopy Study of a Calcium‐Polygalacturonate Network in the Presence of Aluminum: A Model to Investigate Soil‐Root Interface Processes

Abstract

The objective of this study was to investigate the effects of aluminum (Al³⁺) on a calcium‐polygalacturonate (Ca‐PG) network used as a soil‐root interface model. Calcium‐PG networks were exposed to Al³⁺ solutions at different concentrations (100, 200, 400, and 800 µM) at pH 3.50. In the present study, the scanning electron microscopy technique was used to evaluate morphological variations induced by Al³⁺sorption. Results showed how aluminum (Al) sorption induces conformational changes of the Ca‐PG complex. The Ca‐PG complex shows a regular structure with a honeycomb‐like pattern. Interlacing fibrils form a porous system, which can easily allow sorption and/or passage of nutrients as well as toxic elements. As Al becomes the predominant reticulating ion, the pores decrease in size and lose their regular shape. The scanning electron micrographs have in fact shown that Al sorption damages the Ca‐PG complex, leading to its collapse; the Ca‐Al‐PG networks exhibit an irregular uneven structure.     

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.     

Estimation of plant available manganese in acidic subsoil horizons

Abstract

General agreement does not exist as to the most appropriate method to estimate plant available Mn in soils. In the current investigation soil and soil solution Mn were measured in limed and unlimed treatments of 11 acidic subsoil horizons and related to plant Mn concentrations, Mn uptake and growth of subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) and switchgrass (Panicum virgatum cv. Cave‐in‐Rock). Manganese measurements were taken at planting and harvest and included: Mn extracted by 1M NH₄OAc (pH 7), 0.01M CaCl₂, 0.05M CaCl₂, 0.033M H₃PO₄, 0.005M DTPA, 0.2% hydroquinone in 1M NH₄OAc (pH 7), 0.01M NH₂ OH.HCl 4 2 in 0.01M HNO₃, total soil solution Mn and concentrations and 2+ activities of Mn²⁺ calculated from the GEOCHEM program. Measured and calculated values of soil solution Mn generally gave the best correlations with subterranean clover and switchgrass Mn concentrations and Mn uptake. Root Mn concentrations were highly correlated with soil solution Mn measurements taken at harvest with r=0.97 and r=0.95 (p<0.01) for subterranean clover and switchgrass respectively. The Mn extracted by 0.01M CaCl was also significantly correlated (p<0.01) with plant Mn concentrations and Mn uptake and proved to be better than the other extractants in estimating plant available Mn. Although Mn concentrations as high as 1769 mg/kg (shoots) and 8489 rag/kg (roots) were found in subterranean clover, Mn did not appear to be the major factor limiting growth. Measures of soil and soil solution Mn were not strongly correlated with yield. Both Al toxicities and Ca deficiencies seemed to be more important than Mn toxicities in limiting growth of subterranean clover and switchgrass in these horizons.     

Phosphorus Alleviates Aluminum Toxicity in Al-Sensitive Wheat Seedlings

The role of phosphorus (P) in the amelioration of aluminum (Al) toxicity to plants is still unclear. The aim of this study was to examine the amelioration of Al toxicity by P supply. The study involved growing Al-sensitive wheat seedlings for 13 days in an acidic soil [pH 4.5 in calcium chloride (CaCl₂)] with increasing added rates of P (0, 20, 40, and 80 mg P kg^?1 soil) and Al [0, 50, and 150 mg aluminum chloride (AlCl₃) kg^?1 soil]. The results indicated that the effects of Al toxicity in this soil could be fully alleviated by the application of P at 50 mg AlCl₃ kg^?1. The 150 mg kg^?1 AlCl₃ treatment significantly reduced root growth, but this was partially overcome by the 80 mg kg^?1 P treatment. High P significantly reduced the concentration of Al in the apoplast, root, and shoot. It is possible that an insoluble Al-P complex forms in the soil and this decreases Al bound in apoplast as well as uptake into the roots. High P decreased the translocation of Al from root to shoot. This study also concluded that detoxification of Al³⁺ by P mainly occurs in soil but not within the plant tissue.     

Growth of and potassium transport in winter wheat and durum wheat as affected by various aluminum exposure times

Effects of various aluminum (AlCl₃) concentration and exposure times (6, 12, and 24 h and 3 d) on growth and potassium (K) transport were studied in two wheat species (Triticum aestivum L. cv. Jubilejnaja 50 and Triticum durum Desf. cv. GK Betadur) grown in low salt conditions hydroponically. In longer (3 d) Al exposure times at pH 4.1, the inhibition of root growth appeared at 10 μM Al³⁺ treatment in GK Betadur, and at 50 μM Al³⁺ treatment in Jubilejnaja 50. Shoot growth was not influenced by Al³⁺ treatment, except at 100 μM in 7 d experiments. In 6, 12, and 24 h Al³⁺ exposure times, at low pH, the K⁺(⁸⁶Rb) influx in roots increased as the Al³⁺ concentration increased in the outer medium in both species. It also appeared in K⁺(⁸⁶Rb) transport toward the shoots, except by higher Al³⁺ treatments of GK Betadur seedlings. At the same time, in longer‐term (3 d) Al³⁺ treatments, a striking inhibition were observed in K⁺(⁸⁶Rb) influx and K⁺ concentration of roots and shoots. The K⁺concentration of roots and shoots measured at the end of 24 h Al³⁺ exposure times was significantly not affected by Al³⁺ treatment. Durum wheat proved to be more sensitive to the Al toxicity than common winter wheat.     

Speciation and Solubility Control of Aluminium in Soils Developed from Slates of the River Sor Watershed (Galicia,NW Spain)

The Al species in the soid and liquid phases were studied in eight soils developed from slates in a watershed subjected to acid deposition. From soil solution data the mechanisms possibly controlling Al solubility are also discussed. The soils are acidic, organic matter rich and with an exchange complex saturated with Al. In the solid phase, more than 75% of non-crystalline Al was organo-Al complexes, mostly highly stable. In the soil solutions, monomeric inorganic. Al forms were predominant and fluoro-Al complexes were the most abundant species, except in soil solutions of pH<4.8 and Al L/F ratio >3, in which Al³⁺ predominated and sulphato-Al complexes were relatively abundant. The most stable phases were kaolinite, gibbsite and non-crystalline Al hydroxides. In most samples, Al solubility was controlled by Al-hydroxides. Only in a few cases (solutions of pH 4-5, Al³⁺ activity >40 µmol L-¹ and SO₄ content >200 µmol L-¹), Al-sulphates such as jurbanite also could exert some control over Al solubility. In adition to these minerals, a possible role of organo-Al complexes or the influence of adsorption reactions of sulphate is considered, especially for samples with very low Al³⁺ content (<0.5 µmol L-¹).     

Mechanisms of aluminum‐induced growth stimulation in tea (Camellia sinensis)

Beneficial effects of aluminum (Al) on plant growth have been reported for plant species adapted to acid soils. However, mechanisms underlying the stimulatory effect of Al have not been fully elucidated. The aim of this study was to determine the possible contribution of photosynthesis, antioxidative defense, and the metabolism of both nitrogen and phenolics to the Al‐induced growth stimulation in tea (Camellia sinensis [L.] Kuntze) plants. In hydroponics, shoot growth achieved its maximum at 50 μM Al suply (24 μM Al³⁺ activity). A more than threefold increase of root biomass was observed for plants supplied with 300 μM Al (125 μM Al³⁺ activity). Total root length was positively related to root Al concentrations (r = 0.98). Chlorophyll a and carotenoid concentrations and net assimilation rates were considerably enhanced by Al supply in the young but not in the old leaves. Activity of nitrate reductase was not influenced by Al. Higher concentrations of soluble nitrogen compounds (nitrate, nitrite, amino acids) and reduction of protein concentrations suggest Al‐induced protein degradation. This occurred concomitantly with enhanced net CO₂‐assimilation rates and carbohydrate concentrations. Aluminum treatments activated antioxidant defense enzymes and increased free proline content. Lowering of malondialdehyde concentrations by Al supply indicates that membrane integrity was not impaired by Al. Leaves and roots of Al‐treated plants had considerably lower phenolic and lignin concentrations in the cell walls, but a higher proportion of soluble phenolics. In conclusion, Al‐induced growth stimulation in tea plants was mediated by higher photosynthesis rate and increased antioxidant defense. Additionally, greater root surface area may improve water and nutrient uptake by the plants.     

Uptake of aluminum into root cytoplasm: Predicted rates for important solution complexes

In this report we predict the rate of aluminum absorption into root cytoplasm as solutes that are common in acid soil solutions. Our predictions of passive influx rely upon permeability coefficients estimated from known values for similar compounds. We also consider aluminum absorption by endocytosis and absorption by competition with iron for iron‐specific transport mechanisms. Our calculations indicate that passive flux of Al³⁺ or of common charged Al‐complexes is unlikely to contribute measurably to total aluminum absorption , but endocytosis of Al³⁺ bound to the plasma membrane surface may dominate uptake under some conditions. Among neutral Al‐complexes, AlF₃ ^o absorption should be detectable; by comparison, passive influx by Al‐citrate^o should not be detectable.     

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.     

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.     

Ionic Activity in Soil Solution as Affected by Application Of Newsprint and Nitrogen Sources

The influence of noncomposted ground newsprint (GNP) and nitrogen (N) source on corn (Zea Mays L.) dry matter production, grain yield, and soil chemical properties has been previously reported (Lu et al. 1995). The effects of GNP and N source on soil solution ionic activities at 40 days after planting in a field study; seed germination and extractable aluminum (Al) in GNP in laboratory studies were evaluated to determine their effects on corn seedling stunting and nutrient imbalances during early growth stages. Ammonium nitrate (NH₄NO₃), urea, anhydrous ammonia (NH₃), or poultry litter (PL) were the N sources used in the field study to adjust the C:N ratio of the GNP to ≤ 30:1. In laboratory experiments, cotton, soybean, and corn germination at seven days was not affected by N source or GNP applied at a rate of 2.44 kg C/m² soil; but N source did influence the dry weight of corn root/shoot ratio at 21 days. The Al extracted from GNP increased as the NH₄OH concentration in the extracting solution increased and followed a quadratic relationship with an r² of 0.90. The σα_ca/σα_cation ratio in soil solution for all N sources was greater than the 0.15 reported by Bennett and Adams (1970a), where incipient NH₃ phytotoxicity can occur. At 40 days after planting, a two-fold increase in soil monomeric Al (σAlα_mon.) ionic activity and a five-fold increase in soil P (σPα) ionic activity were measured in GNP treatments as compared to no N GNP treatments. When NH₃ was the N source used to adjust the C:N ratio of GNP, the σAlα_mon. ionic activities were increased by a factor of five as compared to NH₃ applied alone. When PL was the N source, the Al_T (σAlα_species) ionic activity was 119 mmol L^?1 compared to the σAlα_mon. ionic activity of 0.53 mmol L^?1. It appears that σAlα_mon. ionic activity induced nutrient disorder and caused severe stunting of corn seedlings during early season growth. The relatively high water-soluble organic carbon in PL (18 percent) may have acted as a chelating agent to reduce the σAlα_mon. ionic activities in the GNP, or as a soluble carbon source for increasing microbial utilization of all the N, thus slowing the formation and accumulation of phytotoxic levels of by-products.