Phosphorus status of some ethiopian soils

The capacity to sorb P varied among some Ethiopian soils. Volcanic ash soils sorbed the maximum P while Fluvisols and Regosols sorbed the least. Sorption of P was significantly correlated with exchangeable and extractable forms of Fe and Al as well as pH and organic matter. But is was not related to the clay content of the soils. The role of Al was more important than that of Fe even though more dithionite and oxalate extractable Fe than Al was found in all soils.     

Effect of algal growth on the availability of phosphorus,iron and manganese in rice soils

Summary Laboratory experiments were conducted to study the effect of algal growth on the change of (I) pH, (II) available phosphorus and (III) solubility of iron and manganese content in five waterlogged alluvial rice soils of West Bengal, India. The results showed that the algal growth initially caused an increase in the soil pH, which later declined to the original value in some of the soils. The available phosphorus content decreased upto 90 days of their growth and began to increase towards the later period of incubation. The drastic fall of water soluble plus exchaneable manganese content of the soils due to algal growth was accompanied by similar increase in reducible manganese content. No appreciable change in water soluble plus exchangeable ferrous iron content was encountered but theN-NH₄OAC(pH 3) extractable iron due to algal growth progressively decreased with the progress of the incubation period.     

Solid-phase distribution of heavy metals as affected by single reagent extraction in dredged sediment derived surface soils

ABSTRACT

EDTA is useful to assess mobile metal pools in polluted soils and sediments. There is a need to enhance our understanding of the significance of metal fractions released. The impact of single reagent extraction with 0.05 mol L^?1 EDTA on the solid phase distribution of trace metals in surface soils sampled from confined dredged sediment disposal sites was investigated. Not extracted and EDTA extracted soils were subjected to sequential extraction to fractionate the total contents into: (1) easily exchangeable and carbonate bound fraction; (2) reducible fraction; (3) oxidisable fraction; and (4) residual fraction. With EDTA, significant portions of metals associated with the acid extractable and reducible fractions were released. The oxidisable and residual fractions remained unaffected for most of the investigated metals except for the organic matter associated metals (Cu and Pb). A decrease in the residual fraction after EDTA-extraction for Cu and Pb was attributed to artifacts of the sequential extraction procedure.     

Determination of total copper and zinc contents of Egyptian soils using three different methods

Summary To compare chemical methods for determining total contents of Cu and Zn in Egyptian soils, surface samples of two groups of soils from Egypt namely the alluvial and the calcareous were chosen. The samples were analyzed for the total Cu and Zn using three chemical methods namely, aqua regia, hydrofluoric acid and fusion methods. The mean values of total Cu determined by aqua regia, hydrofluoric acid and fusion methods were 58.7, 69.2, 69.4 ppm for the alluvial soils and 11.8, 13.0, 12.8 ppm for the calcareous soils respectively. The corresponding values of Zn were 138.6, 189.4, 189.8 ppm for the alluvial soils and 58.6, 89.7, 90.3 ppm for the calcareous soils. The Cu and Zn contents in the alluvial and calcareous soils, determined by the aqua regia method was lower as compared with those determined by the fusion or hydrofluoric methods.An attempt was made to use the etching of soil with aqua regia and the linear relationship, to quantitavely evaluate the total content of Cu and Zn determined with hydrofluoric acid or fusion methods.     

Transformation of iron and manganese in rice soils under different moisture regimes and organic matter applications

Summary Transformation of iron and manganese under three different moisture regimes,viz continuous waterlogged (W₁), continuous saturated (W₂) and alternate waterlogged and saturated (W₃) and three levels of organic matterviz 0, 0.5 and 1.0% in all possible combinations was studied in four soils. The results showed that under waterlogged moisture regime there was a sharp increase in the content of water soluble plus exchangeable manganese accompanied by significant decrease in the content of reducible manganese in all the soils excepting the acidic soil which was very poor in active manganese content. The increase in respect of iron in similar form was, however, very small. The increase in the content of water soluble plus exchangeable manganese as well as iron under the continuous saturated and alternate waterlogged and saturated moisture regimes was always much lower as compared to that under the continuous waterlogged condition. Application of organic matter brought about an increase in the content of water soluble plus exchangeable manganese in all the soils excepting the lateritic one irrespective of moisture regimes but did not cause any change in the content of iron and manganese in insoluble complex. The content of water soluble plus exchangeable iron and of insoluble ferrous iron although recorded some increase due to organic matter application, the increase was not so marked in any of the soils.     

Potential effect of land-leveling on soil fertility in a Brazilian rice soil

Land-leveling to improve water management in lowland rice (Oryza sativa L.) production is becoming common in many countries. This technique exposes subsoil by removal and deposition of surface soil from high- to low-lying areas. The potential effect of land-leveling on soil fertility was studied in samples from an alluvial soil at depths of 0- to 5-, 5- to 15-, and 15- to 25-cm. Levels of soil cation exchange capacity; dilute acid-fluoride extractable P; DTPA extractable Cu, Mn, and Zn; exchangeable K; hot-water soluble B; and organic matter decreased with soil depth; whereas, soil pH increased with depth. Relatively low amounts of dilute acid-fluoride extractable P, exchangeable K, and DTPA extractable Zn occurred in the 15- to 25-cm layer of the soil. These data indicate the high likelihood that K, P, and Zn deficiencies would occur in rice grown on the subsoil that was exposed by land-leveling.     

Fate and Mobility of Copper in Soil of Cocoa Plantations in Two Southwestern States of Nigeria Treated with Copper-Based Fungicides

Soils from cocoa plantations treated with Boudreaux mixture in two southwestern states of Nigeria were collected at different depths, 0–15 cm and 15–30 cm, and subjected to five-stage sequential extraction to obtain the speciation forms of copper: exchangeable, carbonate, manganese and iron oxides, organic and residual fractions. The Cu content in the extracts from the sequential extraction was read with an Atomic Absorption Spectrophotometer (AAS). The total Cu content of the soil and the physicochemical parameters of the soils were also determined. The results from the study showed that the soils had high organic matter and copper is mostly bounded to the more mobile exogenic phase much more than the stable lithogenic phase, indicating higher mobility. Within the exogenic species, carbonate fraction was the highest followed by the organic bound and the exchangeable fraction in decreasing order. Cu was not detected in the Fe/Mn bound fraction. The implication is that the fate of the administered Cu-based pesticide is more in the relatively stable carbonate bound species than the other, more mobile phase. The results showed variation in the distribution of the copper species from one depth to another. The most transported metal from the surface to the lower layer is the exchangeable fraction. The carbonate bound species is less mobile and is not readily transported into the bottom soil layer. The organic bound Cu has nearly equal distribution between the top and bottom soils and there was little or no transport of the residual metal specie from the top to the bottom. The existence of copper in the soil largely in the anthropogenic (exogenous) phase is not the most desirable for the ecosystem. This may increase the availability of Cu in the cocoa plant and bean and may lead to potential exposure risk.     

Experimental Assessment of Using Soluble Humic Substances for Remediation of Heavy Metal Polluted Soils

Since heavy metals are nondegradable and strongly bonded in soils, remediation of heavy metal polluted soils by extraction is difficult and current extraction techniques require harsh chemicals such as ethylenediaminetetraacetic acid (EDTA). However, use of EDTA is environmentally problematic because of costs, persistence, toxicity and deterioration of soil structure. Therefore, the potential of soluble natural humic substances (HS) to extract heavy metals from contaminated soils is tested as an environmentally friendly substitute for EDTA. A strongly polluted, calcareous urban soil (CRC soil) and a moderately polluted agricultural soil (CUP soil) were extracted at neutral pH in batch mode by three HS solutions from beech and Norway spruce litter (Beech-HS and Spruce-HS) and processed cow slurry (Bio-HS), all containing 25 mM dissolved organic carbon (DOC). After 10 extractions with a solution to soil ratio of 5:1 (L/kg), 8% to 39% of the total Cd, Cu, Ni and Pb soil contents, lowest for Ni and highest for Cu/Pb, were extracted. Natural and processed HS samples had comparable capacities to extract the heavy metals. A comparison of 100 mM DOC of Bio-HS and EDTA as extractants for Cu from the CRC soil showed extraction of 67% by EDTA and 41% by Bio-HS, indicating somewhat higher efficiency of EDTA than of HS. Sequential extraction of the CRC soil after Bio-HS and EDTA extraction showed removal of exchangeable, carbonate- and metal oxide-bound Cu but also of some residual Cu. It is therefore concluded that HS appears to be an attractive and promising alternative to EDTA as remediation agent for heavy metal polluted soils provided cheap HS of good quality is easily available.     

Influence of Soil Organic Matter on Copper Extraction from Contaminated Soil

Column experiments of copper extraction from four contaminated soils characterized by a content of Soil Organic Matter (SOM) ranging from 1% to 25% are presented and discussed. The extraction was performed by flushing the soil with an aqueous solution of a sodium salt of ethylene diamminotetraacetic acid (EDTA). Preliminary tests were performed on a soil containing 25% of organic matter, to investigate the influence of pH, concentration and volumes of EDTA on its chelant action and on the dissolution of SOM. Having selected the optimal conditions for the extraction process, a further series of tests was conducted on the four soils to evaluate the influence of organic content on copper extraction yields. EDTA solutions at 0.01 M, 0.05 M, 0.1 and 0.2 M were injected at 0.33 ml/s; copper and organic matter extraction yield were determined. At a pH of 5, 15 pore volume (PV) of a solution containing 0.05M EDTA, extracted about 99% of copper contained by the soil with the higher organic matter content. Under the same conditions, and for soil with > 6% SOM, extraction yields over 80% were achieved, while at lower organic content, copper extraction was dramatically reduced. This was attributed to the formation of highly stable copper-humate complexes and to their increasingly dissolution that occurred in the soils with higher organic matter level.

Experimental tests performed at different contamination levels (1200 mg/kg, 2400 mg/kg) showed that EDTA extraction effectiveness also depended upon initial soil Cu concentration.     

Fractionation of metals in the Sa1/2 sediment core from Lake Sarbsko (northern Poland) and its palaeolimnological implications

Abstract

This article documents and interprets stratigraphical changes in fractionation of Fe, Mn, Mg, K, Pb, Cu and Zn in the Sa1/2 sediment core from a coastal freshwater lake, Lake Sarbsko (northern Poland). The elements were sequentially extracted from the samples to distinguish five geochemical fractions: exchangeable, acid-extractable, reducible, oxidisable and residual. The analyses revealed substantial variations in geochemical partitioning of the elements and showed no correlation between the fractionation patterns and lithology of the sediments. In the sediments of Lake Sarbsko, iron is mainly bound to sulfides. Potassium occurs in its residual form. Magnesium and zinc are associated with carbonates and aluminosilicates, while copper occurs in compounds with organic matter and sulfides. Lead is found in connection with aluminosilicates and, to a lesser extent, with sulfides and organic matter. Manganese is partitioned between the oxidisable, acid-extractable, and exchangeable fractions. Heavy metals and potassium display the overall tendency to reduce the contents of their residual forms towards the top of the depositional sequence. Fe, Mn, Mg and Zn were found to be the most susceptible to post-sedimentary mobilisation.     

Phytoextraction of copper from contaminated soil by Elsholtzia splendens as affected by EDTA, citric acid, and compost

Phytoextraction of copper (Cu) from contaminated soils greatly depends on the metal bioavailability in the soils and metal uptake ability of the plant. In this study, the effects of chelators [ethylenediamine tetraacetic acid (EDTA), citric acid (CA)] and compost amendments on Cu phytoextraction potential by a tolerant and accumulating plant species (E. splendens) were examined in two types of contaminated soils, ie., the mined soil from Cu-mined area (MS) and a paddy soil polluted by Cu refining (PS). The results showed that EDTA application at 2.5-5.0 mmol kg(-1) increased phytoextraction of Cu by four- and eight-fold from both MS and PS, respectively, which is mainly attributed to increased H2O extractable Cu in the soil. The Cu amount extracted by the shoots of E. splendens reached 800-1000 microg Cu plant(-1) from the MS and 400-700 microg Cu plant(-1) from the PS at EDTA application rates of 2.5-5.0 mmol kg(-1). The application of CA at 5.0 mmol kg(-1) had minimal effects on Cu extractability in both soils and slightly decreased Cu extraction efficiency by E. splendens. Plant biomass production was enhanced by CA at 0.25 mmol L(-1) in nutrient solution, but inhibited by CA at 5.0 mmol kg(-1) in both MS and PS. Increasing the compost rate significantly decreased H2O extractable Cu in the MS, but raised H2O-extractable Cu in the PS, which resulted mainly front the reduced exchangeable Cu in the MS and the increased exchangeable and organic fractions of Cu in the PS by compost. At high compost rate (5%), the shoots of E. splendens extracted 3.6-fold higher Cu from the PS than from the MS. These results indicate that, among the soil amendments, efficiency of Cu phytoextraction is enhanced mostly by 2.5-5.0 mmol kg(-1) EDTA, followed by 5% (w:w) compost, whereas < 5.0 mmol kg(-1) CA has minimal effects on Cu phytoextraction by E. splendens in the PS. As for the MS, only 2.5-5.0 mmol kg(-1) EDTA can elevate the efficiency of Cu, while 5% compost amendment and < 5.0 mmol kg(-1) CA application have no marked effects on Cu phytoextraction by E. splendens.     

Transformation of zinc in soils under submerged condition and its relation with zinc nutrition of rice

Laboratory and greenhouse experiments were conducted with two soilsviz., laterite and alluvial to study the transformation of applied Zn in soil fractions under submerged condition in the presence and absence of added organic matter and its relationship with Zn nutrition of rice plants. The results showed that application of organic matter caused a decrease in the concentration of Zn in shoot and root of rice plants and helped in translocating the element from root to shoot. The per cent utilization of applied Zn by plants was also found to increase by the application of organic matter. The transformation of applied Zn in different fractions in soils showed that a major portion (53.6–72.6%) of it found its way to mineral fractions leaving only 1.0–3.3, 6.6–18.9, 11.0–21.6 and 2.3–8.8% of the applied amounts in water soluble plus exchangeable, organic complexed, amorphous sesquioxides and crystalline sesquioxides bound fractions respectively. Application of organic matter favoured such transformation of applied Zn into these fractions except the mineral and crystalline sesquioxides bound ones. Simple correlation and multiple regression analyses between applied Zn in different soil fractions and fertilizer Zn content in plants showed that organic matter application increased the predictability of fertilizer Zn content in plants which has been attributed to the higher per cent recovery of applied Zn in plant available fractions in soils in presence of added organic matter.     

Copper uptake and phytotoxicity as assessed in situ for durum wheat (Triticum turgidum durum L.) cultivated in Cu-contaminated, former vineyard soils

This work assessed in situ, copper (Cu) uptake and phytotoxicity for durum wheat (Triticum turgidum durum L.) cropped in a range of Cu-contaminated, former vineyard soils (pH 4.2–7.8 and total Cu concentration 32–1,030 mg Cu kg⁻¹) and identified the underlying soil chemical properties and related root-induced chemical changes in the rhizosphere. Copper concentrations in plants were significantly and positively correlated to soil Cu concentration (total and EDTA). In addition, Cu concentration in roots which was positively correlated to soil pH tended to be larger in calcareous soils than in non-calcareous soils. Symptoms of Cu phytotoxicity (interveinal chlorosis) were observed in some calcareous soils. Iron (Fe)–Cu antagonism was found in calcareous soils. Rhizosphere alkalisation in the most acidic soils was related to decreased CaCl₂-extractable Cu. Conversely, water-extractable Cu increased in the rhizosphere of both non-calcareous and calcareous soils. This work suggests that plant Cu uptake and risks of Cu phytotoxicity in situ might be greater in calcareous soils due to interaction with Fe nutrition. Larger water extractability of Cu in the rhizosphere might relate to greater Cu uptake in plants exhibiting Cu phytotoxic symptoms.     

Plant indicators of alluvial soils of central Iraq

Summary The alluvial soils of Central Iraq are occupied by 4 main vegetation types. The soils under the riverian vegetation are characterised by medium salinity and high proportions of bivalent cations. The soils occupied by arid scrub vegetation have comparatively higher contents of clay and small amounts of soluble salts. The soils of the halophytic vegetation are highly saline and main component of this is sodium chloride. The soils under the aquatic vegetation are highest in organic matter and low in salinity.     

Solubility relationships of arsenic in calcareous soils and its uptake by corn

Summary The concentrations of total, water-extractable and DTPA extractable As were determined in 19 calcareous soils. The activity of HAsO ₄ ^2– was calculated in the experimental soils and superimposed on the thermodynamic solubility isotherms of As minerals. It was observed that all the soils were undersaturated with respect to Ca₃(AsO₄)₂ and Mn₃(AsO₄)₂ (the most insoluble As minerals in the calcareous soils). The activity of Ca²⁺ in these soils was found to be in equilibrium with CaCO₃.Corn was grown in the experimental soils for 25 days. The corn plants were harvested, dried at 60°C, ground and analyzed for the concentrations of As. The concentrations of As in the plants were significantly correlated (P<0.05) to the water extractable As but not to the total and DTPA extractable concentrations of As in the soils. Sodium bicarbonate extractable P was significantly correlated (P<0.05) to both As in the corn and the water soluble As in the soils.     

Plant indicators of alluvial soils of Central Iraq

Summary The alluvial soils of Central Iraq are occupied by 4 main vegetation types. The soils under the riverian vegetation are characterised by medium salinity and high proportions of bivalent cations. The soils occupied by arid scrub vegetation have comparatively higher contents of clay and small amounts of soluble salts. The soils of the halophytic vegetation are highly saline and main component of this is sodium chloride. The soils under the aquatic vegetation are highest in organic matter and low in salinity.     

Factors affecting metal concentrations in reed plants (Phragmites australis) of intertidal marshes in the Scheldt estuary

We aimed to identify the environmental factors which significantly affect metal uptake by reed plants in the intertidal marshes along the river Scheldt. Transfer coefficients, defined as the ratio of metal concentrations in reed stems to the metal contents in specific sediment fractions (i.e. the exchangeable Cd and Zn fraction and total Cr, Cu, Ni and Pb content), were calculated for each sampling site. They were inversely related to the sediment clay and/or organic matter content. Metal mobility and thus plant availability is higher in sediments with a lower clay or organic matter content. Moreover, the plants might actively accumulate in particular essential elements when concentrations in the sediments are rather low, which is the case in sediments low in clay and organic matter contents. Finally, more sandy sediments are expected to be susceptible to occasional oxidation of sulphides, which leads to an increased metal availability. A higher salinity promoted the uptake of Cu, Cr and Zn.     

Iron-phosphorus relationship in the nutrition of tomato seedlings grown on alluvial and calcareous soils

Summary In typical alluvial and calcareous soils of Egypt 5 levels of each of P and Fe were added to study their effect on the dry matter and on their uptake by tomato seedlings in greenhouse. Application of phosphorus significantly increased the dry matter yields and both P and Fe uptake by tomatoes grown on both soils. However, application of Fe had no significant effect on the dry matter and P-uptake by tomatoes grown on alluvial soil while they were significantly increased on the calcareous one.     

Effect of organic materials addition on transformation of added manganese dioxide to alkali calcareous soils

Summary A study was made of the effect of addition and incubation of two organic materials to two alkali calcareous soils on the transformation undergone by added MnO₂. It is found that decomposition of added organic materials has a solubilizing effect on soil Mn and the added MnO₂ as it resulted in a temporary marked increase in water-soluble plus exchangeable Mn. This increase was accompanied by a decrease in the easily reducible Mn suggesting that part of it is transformed to the divalent form. The intermediate decomposition products form complexes with Mn which are soluble at the pH range of alkaline soils. A great part of the added MnO₂ was recovered in the easily reducible form while it was not extracted by the Na₂-EDTA solution. However, the Na₂-EDTA extractable Mn increased appreciably upon MnO₂ and organic materials addition and incubation, suggesting that part of the added oxide is transformed to the insoluble chelated form. A new hypothesis on the Mn cycle in soils is presented. It is based on oxidation-reduction, and production and decomposition of natural chelating agents during incubation.     

Plant availability of applied and native boron in soils with diverse properties

Laboratory and greenhouse research was conducted to study effects of soil properties on the availability of native and applied B in 14 Virginia soils. Boron absorption could be described by the Langmuir equation in 12 of the 14 soils, and maximum B adsorption (Vmax) in these 12 soils ranged from 3.3 to 26.5 mg kg⁻¹. A multiple regression equation, −19.3+3.51 pH+0.048 clay content, accounted for 89.6% of the variation in Vmax for the 12 soils. Curvilinear relationships (α=0.01) occurred between B in corn (Zea mays L.) tissue from native B and hot-water soluble B, mannitol exchangeable B, and NH₄-acetate and Mehlich III extractable B. Among these four procedures, mannitol exchangeable B correlated most closely (r=0.923) with B in corn tissue from native B. From 0.4 to 13.5% of the applied B was absorbed by corn plants and translocated to shoots. Curvilinear relationships (α=0.01) occurred between B in corn tissue from applied B and soil clay content, NH₄-oxalate extractable Al and Fe, and acidified NH₂OH·HCl extractable Mn. It is evident from these relationships that soil clay and oxyhydroxides of Al, Fe, and Mn have an affinity to adsorb B in somewhat unavailable forms.