Effect of steel-making slag as a soil amendment on arsenic uptake by radish (Raphanus sativa L.) in an upland soil

The steel-making slag (SMS), a by-product of steel manufacturing process with an alkaline pH (11–12) and high amount of iron (Fe) and calcium (Ca) oxides, was used to reduce arsenic (As) phytoextractability. The by-product was selected as an alternative to commercial Fe oxides, which can decrease plant uptake, but they are expensive if used as amendments of contaminated arable soils. SMS was applied at rates 0, 2, 4, and 8 Mg ha⁻¹ to an As (1 N HCl-extractable As 25 mg kg⁻¹) contaminated soil prepared by mixing non-contaminated soil and mine tailings and cropped to radish (Raphanus sativa L.) seeding. Calcium hydroxide (Ca(OH)₂), a common liming material in Korea, was applied at the same rates for comparison. Steel-making slag more effectively suppressed radish As uptake and increased yield than Ca(OH)₂ due to stronger As immobilization because it significantly increased extractable Fe concentration and decreased extractable As. The SMS-treated soil showed an apparent increase in As chemisorbed by Fe and Al oxides and hydroxides of surface soil, As associated at the Fe and Al oxides and hydroxides of internal surfaces of soil aggregates, and Ca-associated As. The steel-making slag can be a good soil amendment to suppress As phytoextractability and improve nutrient balance in As-contaminated soil.     

Comparative Effect of Two Different Types of Phosphate on Cadmium Uptake by Radish (Raphanus sativa L.) Grown in Arable Soil Affected by Mine Activity

To evaluate the effect of type of phosphate (P) material on reducing soil cadmium (Cd) extractability and radish Cd uptake in the field, two different P materials, fused superphosphate (FSP) and dipotassium phosphate (K₂HPO₄), were applied at rates of 0, 33.5, 100.5, and 167.5 kg P ha^?1 before seeding radish (Raphanus sativa L.) in a Cd-contaminated soil. Plant-available Cd concentration in soil and total Cd uptake by radish increased with increasing FSP application but decreased with K₂HPO₄. The significant decrease in soil pH and negative charge of soil by FSP application led to an increase in bioavailable Cd fraction in soil and in Cd uptake by radish. However, K₂HPO₄ increased soil pH and negative charge of soil and decreased bioavailable Cd fractions. Soil pH and negative charge of soil played an important role in controlling Cd uptake by radish in soil to which phosphate was applied.     

Soil pH influence on cadmium uptake by tobacco in high cadmium exposure

Cadmium (Cd) is a non‐essential toxic element, which is highly accumulated by tobacco leaves and is transferred to tobacco smoke thus contributing substantially to the permitted level of Cd intake by humans. Therefore, measures to reduce Cd accumulation by tobacco are of significant importance. The purpose of the present study was to investigate the influence of soil liming on Cd uptake by tobacco plants in high Cd exposure. A pot experiment was conducted with Nicotiana tabacum L. Samsun 53 on an acid Typic Haploxeralf amended with refuse sugarbeet lime to obtain a pH range from 5.3 to 7.0 and contaminated with 20 mg kg^‐1 Cd applied as CdCl₂. Tobacco was grown in pots for three months under natural conditions, harvested in four cuts and Cd uptake by leaves was estimated. In soil samples selected, pH, Cd extracted by DTPA method, and Cd fractions such as exchangeable, organically bound, carbonate and residual were determined. The results showed that Cd uptake influenced negatively tobacco yield. Soil liming decreased Cd uptake by tobacco plants. The DTPA method was not a good indicator for Cd availability in tobacco. A very strong relationship was recorded between exchangeable Cd and total Cd uptake showing that this Cd fraction is available to tobacco plants. Soil pH was correlated strongly in a negative way with this Cd fraction suggesting that this soil factor is very important in controlling Cd accumulation by tobacco.     

Effect of Lherzolite on Chemical Fractions of Cd and Zn and their Uptake by Plants in Contaminated Soil

Immobilizing materials such as lherzolite could reduce metal bioavailability but the effectiveness of lherzolite on the extractability and bioavailability of cadmium (Cd) and zinc (Zn) is rarely investigated. We conducted a greenhouse experiment to investigate the effect of 5% application of lherzolite to a contaminated soil on the chemical fractionation of Cd and Zn and their uptake by radish (Raphanus sativus L.) and Japanese mustard spinach (Brassica rapa L. var. perviridis). Both plants were grown in a highly contaminated (with Cd and Zn) sandy loam soil. Plants were cultivated consecutively three times in the same pots. After the third cultivation, soil samples were collected and analyzed by sequential extraction procedure into five operationally defined fractions (F1—exchangeable, F2—carbonate-bound, F3—oxides-bound, F4—bound with organic matter, and F5—residual). Addition of lherzolite to soil decreased 50% of exchangeable (F1) Cd but it increased the carbonate (F2), oxide (F3), and organic (F4) fraction Cd. For Zn, application of lherzolite resulted into the reduction of both F1 (87%) and F2 (33%) fractions but it increased the F3, F4, and F5 fractions. The reduction in exchangeable fraction of Cd and Zn in the soil resulted in higher plant growth and lower concentrations of both Cd (64% to 92%) and Zn (78% to 99%) in plant tissues of both plant species grown. We may thus conclude that application of lherzolite resulted into lower availability of these metals in the soil leading to lower uptake of Cd and Zn by plant roots, lower toxicity, and ultimately higher plant growth.     

Liming effects on soil pH and crop yield depend on lime material type,application method and rate,and crop species: a global meta-analysis

Purpose

The aim of this meta-analysis was to investigate the interactive effects of environmental and managerial factors on soil pH and crop yield related to liming across different cropping systems on a global scale.

Materials and methods

This study examined the effects of liming rate, lime application method, and liming material type on various soil chemical properties and crop yield based on data collected from 175 published studies worldwide since 1980.

Results and discussion

The most important variables that drive changes in soil pH and crop yield were liming rate and crop species, respectively. Soil conditions, such as initial soil organic matter and soil pH, were more important for increasing soil pH in field-based experiments, while lime material type and application method were more important for improving crop yield. To effectively neutralize soil acidity, the optimum liming duration, rate, and material type were?<?3 years, 3–6 Mg ha^?1, and Ca (OH)₂, respectively. Averaged across different crop species, the application of CaO, CaCO₃, Ca (OH)₂, and CaMg (CO₃)₂ increased yield by 13.2, 34.3, 29.2, and 66.5%, respectively.

Conclusions

This meta-analysis will help design liming management strategies to ameliorate soil acidity and thus improve crop yield in agroecosystems.

     

Applications of fertilizer cations affect cadmium and zinc concentrations in soil solutions and uptake by plants

A pot experiment was conducted to study changes over time of Cd and Zn in soil solution and in plants. Radish was grown in a soil which had been contaminated with heavy metals prior to 1961. Constant amounts of a fertilizer solution (NH₄NO₃, KNO₃) were added daily. Soil solution was obtained at intervals by displacement with water. The cumulative additions of small amounts of fertilizers were made equal to the plants' requirements at the final harvest but were found to exceed them during most of the experiment. Excess fertilizers caused substantial increases of major (K, Ca, Mg) and heavy-metal (Cd, Zn) ions in soil solutions and a decrease in soil pH, probably due to ion-exchange mechanisms and the dissolution of carbonates. Uptake of Cd and Zn into leaves was correlated with the mass flow of Cd (adjusted r²= 0.798) and Zn (adjusted r²= 0.859). Uptake of K, Ca and Mg by the plants was independent of their concentrations in solution. It is concluded that, in order to study effects of plants on heavy-metal availability and obtain soil solution that has not been altered by fertilizer ions, nutrients must be added according to the needs and growth of the plants. This could be achieved by linking fertilizer additions to the rate of transpiration, as nutrient uptake and transpiration were closely correlated in this experiment.     

Response of acid sulphate soils to different liming treatments II. Exchangeability of soil cations

Liming-induced changes in cation exchangeability were studied in six samples from acid sulphate soils (pH 3.9-4.7) incubated with water or with equivalent quantities of Ca(OH)₂ or KOH. The extractability of acid cation species susceptible to hydrolysis was shown to be affected not only by increased pH but also by the kind of the cation and related electrochemical properties of the base used. Both liming treatments practically eliminated the exchangeable Al. In the virgin soils, however, the polynuclear Al-complexes formed by Ca(OH)₂ treatment seemed to have been hydrolyzed further. The superiority of Ca(OH)₂ was assumed to be due to the higher valency of its cation and its act of provoking a higher increase in ionic strength. The liming agents affected to varying extents also the extractability of base cations. Exchangeable soil K seemed to decrease by the KOH treatment and the soil Ca by the Ca(OH)₂ treatment, whereas K and Ca were only slightly, if any, affected by the Ca(OH)₂ and KOH treatments, respectively. Thus, the reductions were assumed to be attributable to other factors than increased pH. A fixation of K and a possible precipitation of Ca as CaSO₄ were discussed. Ca(OH)₂ decreased in all soil samples the exchangeability of Mg more than did KOH. The depression was not related to the Al polymerization and, thus, cannot entirely be ascribed to specific sorption on Al gel. The results imply that liming may affect base cation exchange reactions by neutralizing exchangeable Al of high bonding strength and by replacing it by cations of the liming agent.     

Liming and Boron in a Teak Crop Established during Early Stages in an Acid Soil

Cultivation of a teak crop in acid soils needs adequate agronomic management of these characteristics of high acidity and low nutrient supply to obtain high yields in wood. This work evaluated the effect of liming and application of boron in teak plants during early stage of growth in acid soils from Córdoba, Colombia. The experiments were conducted in the greenhouse and soils laboratory of the Faculty of Agricultural Sciences by using acid soil limed with calcium hydroxide (Ca(OH)₂) and fertilized with boron. The treatments were chosen according to the Box Bernard augmented matrix 3, with dosages of Ca(OH)₂ from 300 to 5700 kg ha^?1 and boron from 0.3 to 5.225 kg ha^?1, using three repetitions per treatment. Data obtained on boron in the soils (Bs) and in the plant (Bp), foliar area (AF), leaf dry mass (MSH), and roots (MSR) were analyzed through means tests and regressions from response surfaces (p ≤ 0.05). The results indicated increased pH and in the soil’s exchangeable calcium (Ca). To reach the maximal AF, the dosages of 2.26 kg ha^?1 of boron (B) and 4522.6 kg ha^?1 of Ca(OH)₂ were estimated; for MSH, stem, and roots boron, dosages ranged between 2.02 and 5.225, with the dosage of 5700 kg ha^?1 of Ca(OH)₂ in all the variables evaluated. Application of calcium hydroxide also showed positive effect in leaf, stem, and MSR gain of teak seedlings during early growth stages. Fertilization with boron (B) did not show significant effect upon growth of dry masses of the parts evaluated.     

Liming reduces nitrogen uptake from chemical fertilizer but increases that from straw in a double rice cropping system

Liming materials are widely applied to alleviate soil acidification and increase rice yield in acidic soils, but their effects on nitrogen (N) use efficiency are still unclear. Here, we conducted a field-, pot-, and micro-plot experiment to investigate how the application of slaked lime (i.e., Ca(OH)₂) affects the fate of chemical fertilizer-N and straw-N in a double rice cropping system. In the field experiment, liming increased grain yield and N uptake by an average of 9.0% and 10.6%, respectively. In contrast, CaCl₂ application did not affect rice yield and N uptake, suggesting that the effects of lime application were not related to the addition of Ca²⁺. Results from a ¹⁵N tracer experiment (i.e., ¹⁵N-labeled urea and straw) indicated that liming reduced N uptake from fertilizer (−5.7%), but increased N uptake from straw (+31.3%). Liming also reduced soil retention of both urea- and straw-N and increased their loss rates. Taken together, our results indicate that although liming increases rice yield and N uptake, it lowers the use efficiency of fertilizer N and facilitates N losses. In addition, our results emphasize the need for long-term studies on the impact of liming on soil N dynamics in paddy soils.     

Bioavailability of heavy metals and abundance of arbuscular mycorrhiza in a soil polluted by atmospheric deposition from a smelter

The bioavailability of heavy metals (Cd, Zn, Pb, Cu) and the abundance of arbuscular mycorrhiza (AM) were studied in two agricultural fields close to a Pb-Zn smelter and three fields outside the pollution zone all cultivated with maize (Zea mays L.). Metal extractability with ethylenediaminetetraacetic acid (EDTA)-NH₄OAc and Ca(NO₃)₂, plant metal uptake, and mycorrhizal parameters (spore number, root colonization) were assessed at two growth stages (six-leaf and maturity). Despite regular liming, the availability of Cd, Zn, and Pb was markedly higher in the two metal-polluted fields than in the three uncontaminated fields. However, the AM abundance was not correlated with metal availability. Root colonization and spore numbers in the metal polluted fields were relatively high, though at plant maturity the former was significantly lower than in one of the uncontaminated fields. The very low AM abundance in the two other unpolluted fields was related to other factors, particular soil and plant P status and soil pH. AM root colonization did not substantially prevent plant metal accumulation, since the metal concentrations in maize grown on the polluted fields strongly exceeded normal values, and for Cd and Pb reached the limits of toxicity for animal feed.     

Zinc,copper, and nickel availabilities as determined by soil solution and DTPA extraction of a sludge‐amended soil

Abstract

Extracting sludge‐amended soil with DTPA does not always give a reliable measure of plant‐available heavy metals. The major purpose of this greenhouse pot study was to help explain why. Two anaerobically digested sludges from sewages treated with either Ca(OH)₂or FeCl₃were applied to 3‐kg samples of a Mollic Albaqualf previously limed with Ca(OH)₂rates of 0, 2.5, and 10g/pot that resulted in pHs in the check pots of 5.4, 6.2, or 7.7 after the first harvest. Sludge rates provided 0, 200, 40, 800, and 1600 mg Zn kg^‐1of soil. Two consecutive crops of soybeans (Glycine MaxL.) were grown for 42 d each in the greenhouse. DTPA‐extractable, soil‐solution, and plant concentrations of Cu²⁺, Ni²⁺, and Zn²⁺were measured.

Dry matter yields were depressed due to salt toxicity, while DTPA‐extracted Cu²⁺correlated with plant uptake of Cu²⁺for both sludges. DTPA‐extracted Ni²⁺also correlated with plant Ni²⁺from the Ca(OH)₂‐sludge‐amended soil, although DTPA‐extracted Ni²⁺did not correlate with plant uptake of Ni²⁺from the FeCl₃‐sludge‐amended soil, DTPA‐extracted Zn did not correlate with plant uptake of Zn²⁺from any sludge‐amended soil. Soil‐solution composition correlated with plant uptake of Cu²⁺and Ni²⁺in both sludges; it also correlated with plant uptake of Zn²⁺from FeCl₃‐sludge‐amended soil but not from Ca(OH)₂‐sludge‐amended soil. DTPA extraction probably failed with Ni²⁺and Zn²⁺because of (i) its ineffectiveness at low pH, (ii) the inability of DTPA to buffer each soil extract near pH 7.3, and (iii) increased amounts of soluble chelated micronutrients at higher sludge rates and higher soil pHs. Soil‐solution composition seemed to fail only where micronutrient cations in solution probably were present largely as organic chelates     

Bioavailability of Cd and Zn in soils treated with biochars derived from tobacco stalk and dead pigs

Purpose

Previous studies show that application of biochar can reduce the bioavailability of heavy metals in soil. A plant growth experiment was carried out to evaluate the effect of tobacco stalk- and dead pig-derived biochars on the extractability and redistribution of cadmium (Cd) and zinc (Zn) in contaminated soil, and the impact on tobacco (Nicotiana tabacum L.) plant growth.

Materials and methods

The top 20 cm of a soil contaminated with Cd and Zn was used in this study. Biochars derived from tobacco stalk and dead pig were applied to the soil at four application rates (0, 1, 2.5, and 5 %), and tobacco plants were grown. After 80-days growth, the pH, electrical conductivity (EC), CaCl₂-extractable heavy metals and fractions of heavy metals in soil samples, as well as the plant biomass and the concentrations of heavy metals in the plant were determined.

Results and discussion

The plant growth experiment demonstrated that tobacco stalk biochar and dead pig biochar significantly (P?<?0.05) increased the pH, but had no significant effect on the electrical conductivity (EC) of the soil. The CaCl₂-extractable Cd and Zn content decreased as the application rates increased. The concentration of extractable Cd and Zn decreased by 64.2 and 94.9 %, respectively, for the tobacco stalk biochar treatment, and 45.8 and 61.8 %, respectively, for the dead pig biochar treatment at 5 % application rate. After biochar addition, the exchangeable Cd was mainly transformed to fractions bound to carbonates and Fe-Mn oxides, while the Zn was immobilized mainly in the fraction bound to Fe-Mn oxides. Tobacco stalk biochar increased the tobacco plant biomass by 30.3 and 36.2 % for shoot and root, respectively at the 5 % application rate. Dead pig biochar increased the tobacco plant biomass by 43.5 and 40.9 % for shoot and root, respectively, at the 2.5 % application rate. Both biochars significantly (P?<?0.05) decreased the Cd and Zn accumulation by tobacco plant.

Conclusions

As a soil amendment, tobacco stalk biochar was more effective at removing Cd, whereas dead pig biochar was more effective at removing Zn, and a higher application rate was more effective than a lower application rate. Overall, biochar derived from tobacco stalk was more effective, than dead pig biochar, at remediating soil contaminated with Cd and Zn, as well as promoting tobacco growth.

     

Amelioration of cadmium stress in gladiolus (Gladiolus grandiflora L.) by application of potassium and silicon

Gladiolus corms were grown in media contaminated with cadmium (Cd) (50 mg kg^?1) and supplemented with silicon (Si) and potassium (K). The role of Si and K for mitigation of Cd toxicity was evaluated. Cd-induced stress generated significantly increased level of oxidative stress markers including hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) in gladiolus. The application of K and Si improved the production of protein and proline in the treated plants. Moreover, K and Si supplemented plants exhibited an improvement in the activity of antioxidant enzymes and a reduction in the level of MDA, H₂O₂ and Cd uptake under Cd stress. Application of K and Si also enhanced the uptake of mineral nutrients including calcium (Ca), magnesium (Mg), manganese (Mn), sulfur (S) and K. The plants supplemented with K and Si exhibited a higher amount of total phenolics and flavonoids. The combined effect of Si and K was more pronounced regarding beneficial effects on gladiolus plants compared to individual effect of these elements under Cd stress. The current research reveals that Si and K may improve gladiolus growth by decreasing the oxidative stress and Cd uptake and by increasing the activity of antioxidant defense enzymes, the quantity of secondary metabolites and plant nutrition.     

Effect of liming central European loess soils on soil extractable phosphorus and potassium as determined by electro-ultrafiltration

The benefits of liming acidic or calcium (Ca)-deficient soils for soil structure and fertility are well documented. However, little is known about the effect of liming nearly neutral loess soils – lacking Ca – on interactions between soil nutrients. Over a 2-year period, 62 field trials were conducted in Germany and Austria with three treatments (0, 3 and 12 t CaO ha^?1) on slightly acidic loess soils. Soil samples from the top soil layer were taken 4, 8, 16 and 24 weeks after liming. In addition to the pH_CaCl2, the phosphorus (P), potassium (K) and Ca contents were analysed using electro-ultrafiltration (EUF). The application of lime increased the pH in average from 6.6 up to 7.0 and 7.2, but did not decrease EUF extractable P and K below the level of untreated control. Contrary to our expectations, EUF extractable P increased 4 weeks after liming in the treatment with 3 t CaO ha^?1. At the end of incubation period, 24 weeks after liming, the EUF extractable K in treatment 12 t CaO ha^?1 remained still 1.3 mg K 100 g^?1 soil above the untreated control.     

Time Course Transformations and Fate of Mercury in Aquatic Model Ecosystems

In order to achieve remediation of contaminated substrates, phyto-extraction in pot experiments utilizing lettuce seedlings as universal accumulator plants was investigated. As test substrates, mine tailings from Shiheung and Okdong mines in Korea (particularly high in Pb, Zn, Cu, and Cd), as well as samples from historic mining site at Oberzeiring in Austria (particularly high in Pb, Sb and As) were used, and compared with adjacent farmland soils. After 21 days of growth in the test substrate, the lettuce plants were harvested, and the adjacent soils parted in bulk and root soils. Special soil bacteria, adapted to high Cd levels (Exiguobacter sp.) and capable of adsorbing large amounts of cadmium from solution, as well as perlite (Samson Perlite Inc.) were added to the test substrates before plant growth. Speciation changes in the solids were investigated by sequential leaching, utilizing neutral MgCl₂ (exchangeable), 0.16 M acetic acid, hydroxylamine pH 2, oxalate pH 3, H₂O₂ oxidation, and reflux with aqua regia. Plant growth induced differentiation between root and bulk soils, the differences were more pronounced for the non-contaminated controls. The iron-hydroxide phase increased about 30%, and also the amount of iron-hydroxide bound Be, Cd, Co, Cu, Mg, Mo, Sb and V concentrations, coming mainly from less mobile fractions. The Mn hydroxide phase, however (hydroxylamine), remained rather constant. After plant growth, the root soils were significantly lower in available P, and significantly higher in available Ca, Mn, and Na than the corresponding bulk soils. Addition of Cd-adapted soil bacteria led to a severe decrease of plant yield, but metal uptake changed in both directions. Exchangeable P in both root and bulk soil decreased, and Be, Co, Cr, Fe, K, Li, Mg, Mn, Ni, and Sr in the residual organic fraction increased. This can be interpreted as competition for nutrients, dissolution of residuals by bacterial action, and adsorption to a tightly bound biomass. Addition of perlite hardly affected the plant yield, and again metal uptake changed in both directions, but led to a decrease of siderophilic elements in the Fe- and Mn hydroxides of the bulk soil. In the root soil, perlite addition above all decreased available K, P and As, with respect to the untreated samples. Bacteria addition to perlite treated soils shifted some elements from weak acid mobile towards less available fractions.     

Phytoextraction of Cadmium and Phytostabilisation with Mugwort (Artemisia vulgaris)

Artemisia vulgaris (mugwort) is a tall (1.0?C2.0 m) high biomass perennial herb which accumulates considerable amounts of metals on contaminated sites. An outdoor pot experiment was conducted on a sandy, slightly alkaline soil of moderate fertility to study the uptake of cadmium and the distribution of Cd in plant tissues of A. vulgaris. Cadmium was applied as CdCl₂ (a total of 1 l solution of 0, 10, 50 and 100 mg Cd l^?1) to 12-l pots with a height of 25 cm. HNO₃- and water-extractable concentrations of Cd were correlated with the applied Cd at 2-cm soil depth, but were not correlated at 20-cm soil depth, suggesting that Cd was either not mobile in the soil or completely taken up by mugwort roots. The Cd concentrations in different organs of A. vulgaris and litter increased with increasing soil contamination. Leaf/soil concentration ratios (BCFs) up to 65.93?±?32.26 were observed. Translocation of Cd to the aboveground organs was very high. The leaf/root Cd concentration ratio (translocation factor) ranged from 2.07?±?0.56 to 2.37 ± 1.31; however, there was no correlation of translocation factors to Cd enrichment, indicating similar translocation upon different soil contamination levels. In summary, A. vulgaris is tolerant to the metal concentrations accumulated, has a high metal accumulating biomass and accumulates Cd up to about 70% in the aboveground parts. Both a high phytoextraction potential and a high value for phytostabilisation would recommend mugwort for phytoremediation.     

Effect of water treatment sludge on growth and elemental composition of tomato (Lycopersicon esculentum) shoots

Abstract

The impact of a water treatment sludge on the fertility of a silt loam soil was assessed by monitoring the yield and elemental composition of tomato (Lycopersicon esculentum) shoots in a greenhouse study. Application of sludge at rates from 2–10% (air dry weight basis) raised the soil pH from 5.3 to 8.0 which enhanced plant growth. A substantial reduction in metal (Cd, Zn, Cu, Ni) uptake was observed with sludge amendments, even at the highest rates. The alkaline nature of this sludge (pH=9.3, calcium carbonate equivalence=53%) suggests its potential use as a liming material for agricultural soils. Overly alkaline conditions should be avoided however, as high application rates combined with ammonia fertilization had an antagonistic effect on plant growth, possibly from P deficiency induced by struvite (MgNH₄PO₄) formation.     

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.     

Effect of Cattle Slurry on the Growth of Spinach Plants in Cd-contaminated Soil

ABSTRACT

In this work the effect of the addition of different amounts of cattle slurry (CS) to a Cd contaminated soil, was studied regarding its effect in spinach plants. Two levels of Cd contamination (2 and 10 mg/kg) and three levels of CS addition were evaluated (2.5, 5 and 10 g CS/100 g soil). Spinach was shown to be a tolerant species, able to accumulate relatively high amounts of Cd (up to 367.7 mg/kg in the leaves), exceeding the limits established by European regulations for leaf vegetables. The addition of 2.5 and 5 g CS/100 g to soil containing 2 mg/kg Cd did not reduce the uptake of this metal but allowed the plants to grow as much as the control. The addition of 10 g CS/100 g lead to a reduced Cd uptake but also to a lower plant growth compared to the lower CS levels. The combined effects of Cd and CS changed element content in the plant, but without causing severe toxicity or deficiency effects.     

Liming and nitrogen efficiency: Some effects of increased calcium supply and increased soil pH on nitrogen recovery by perennial ryegrass

Abstract

Positive effects of liming on the nitrogen (N) contents of perennial ryegrass (Lolium perenne) shoots might be due in part to the effects of increased exogenous calcium (Ca) level on the rate of N uptake by plants. To test this hypothesis, perennial ryegrass was grown in soil culture treated with different rates of lime, gypsum, and ammonium nitrate (NH₄NO₃), in a factorial combination. The effects of these treatments on yield, N offtake, and shoot chemical composition were examined at two consecutive harvests. At both harvests, liming significantly increased plant yield and N offtake. There was no response to gypsum at cut 1; but at the second harvest, a negative interaction occurred between the two Ca treatments such that gypsum increased plant yield and N offtake in the absence of lime but not in its presence. The results suggest that liming affects N recovery by swards in at least two different ways, each associated with a different phase in the soil MIT (Mineralization Immobilization Turnover) cycle. During phases of net N mineralization, liming by raising soil pH stimulates biomass activity and increases the amount of organic N mineralized. In contrast, during phases of net N immobilization, liming by increasing Ca availability in the rhizosphere improves the ability of plants to absorb N, and thus helps them to compete more effectively with the biomass for mineral N.