pH Ca Research Articles

Electrochemical and XPS surface analytical studies on the reactivity of enargite

Enargite, a copper arsenic sulfide having the formula Cu 3 AsS 4 , is a source of arsenic and may cause environmental problems owing to the release of toxic elements upon oxidation, especially in acid mine effluents. In this work the oxidative dissolution of enargite has been studied on freshly cleaved samples exposed to distilled water, sulfuric acid solution at pH 4 and acidic FeCl 3 or Fe 2 (SO 4 ) 3 solutions at pH ca . 2 with 0.025 M Fe 3+ simulating abiotic acid mine drainage environments. The open circuit potential of the acidic solutions with ferric ions achieved stabilization at + 0.72 ± 0.02 V NHE thus, according to the mixed potential theory, the redox couple Fe 3+ /Fe 2+ strongly polarizes the enargite surface towards positive potentials. Solution analyses showed that in these conditions about 10–14 μg copper are released every 24 h into solution from approximately 0.5 cm 2 enargite surface. Based on the amount of dissolved copper, the thickness of the dissolved enargite has been calculated to be about 60–130 nm. XPS analyses of the reacted enargite surfaces revealed no changes in the binding energy of copper Cu2p3/2 found at 932.4 ± 0.2 eV, arsenic As3d5/2 found at 43.3 ± 0.2 eV and of sulfur, S2p3/2 at 161.9 ± 0.2 eV compared to the pristine surface, whereas a prominent sulfur signal appeared at ca. 163.5 ±0.2 eV, assigned to sulfur in a copper-deficient layer. The XPS quantitative analysis performed by applying a three-layer model revealed the presence of a metal-deficient layer of ca. 0.7 nm thickness on the enargite surface. The interface beneath this layer (estimated thickness 5–10 nm) was slightly enriched in sulfur and depleted in copper. Based on these complementary data from solution analysis and XPS surface analysis, a model similar to the dissolution of binary metallic alloys is here proposed for enargite dissolution under oxidizing conditions.

Heavy Metals in Aquatic Macrophytes from Two Small Rivers Polluted by Urban, Agricultural and Textile Industry Sewages SW Poland

This article presents the results from a study of the comparison of 2 lowland rivers: the Olobok and the Pilawa in southwest Poland polluted by urban, agricultural, and textile industry sewages. pH and concentrations of Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Zn, nitrate, nitrite, ammonia, phosphate, and sulfate were measured in water samples and concentrations of Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, Ni, P, Pb, S, and Zn were measured in stream bottom sediments and in the aquatic macrophytes Elodea canadensis, Callitriche verna, Potamogeton crispus, Potamogeton natans, and Ceratophyllum demersum from the river Olobok and Elodea canadensis, Polygonum amphibium, Potamogeton crispus, and Veronica beccabunga from the river Pilawa. The matrix of concentrations of 16 elements in 27 plant samples of 7 species from 15 sampling sites of 2 rivers and concentrations of 15 elements and pH in water samples and 16 elements and pH in bottom sediment samples of these sites was submitted to numerical classification, which revealed that sampling sites from the rivers were differentiated by the value of factor 1 of principal component analysis (PCA), which was related to the pH of water, Ca, Cu, Mg, Mn, and Ni in water and Cd, Cr, Cu, Fe, K, Mg, Na, Ni, P, and S in bottom sediments. More polluted parts of both rivers were differentiated from less polluted parts by the value of factor 2 of PCA, which was related to Pb, Zn, and sulfates in water and Ca and Zn in bottom sediments. Macrophytes from the Olobok and Pilawa rivers were differentiated by the value of factor 1, which was related to Ca, Co, Cr, Cu, Fe, Mg, Ni, N, Na, Pb, and S. Groups of macrophytes of more and less polluted parts of both rivers differed by the value of factor 2, which was related to P, K, and Mn. Downstream of the sewage outputs in both rivers, a significantly increased level of pollution occurs with elements correlated with factor 1: Among others were Cu and Cr, typical for the textile industry along the river Pilawa, and among others were Mn and Ni, typical for the urban and agricultural activities in the river Olobok.

Assessment of groundwater quality and contamination problems ascribed to an abandoned uranium mine (Cunha Baixa region, Central Portugal)

The assessment of groundwater quality and its environmental implications in the region of the abandoned Cunha Baixa uranium mine (Central Portugal) was carried out from 1995 to 2004. Shallow groundwater is the major water supply source for irrigation in the neighbourhood of Cunha Baixa village. Water samples from the mine site as well as from private wells were collected in order to identify the mining impact on water composition, the extent of contamination and the seasonal and temporal groundwater quality variations. Some of the sampled private wells contain waters having low pH (<4.5–5) and high values of EC, TDS, SO4, F, Ca, Mg, Al, Mn, Ni, U, Zn and 226Ra. The wells located through the ESE–WSE groundwater flow path (1 km down gradient of the mining site) display the most contaminated water. In the summer season, the levels of SO4, Al, Mn, and U were 50–120 times higher than those registered for uncontaminated waters and exceeded the quality limits for irrigation purposes, presenting soil degradation risks. Nevertheless, this study indicates that groundwater contamination suffered a small decrease from 1999 to 2004. The bioaccumulation of toxic metals such as Al, Mn, and U within the food chain may cause a serious health hazard to the Cunha Baixa village inhabitants.

Pinus virginiana invasion influences soils and arbuscular mycorrhizae of a serpentine grassland1

Abstract Serpentine grasslands support a unique endemic flora composed of many rare species that are tolerant of the inhospitable soil conditions characteristic of ultramafic soils. In the eastern United States, rare plants of many serpentine grasslands are being displaced as a result of invasion by Pinus species and consequent changes in environmental conditions. Community structure and function of symbiotic soil arbuscular mycorrhizal fungi (AMF) also may be affected by Pinus succession. This study examined changes in soil properties, AMF communities, and plant growth in serpentine grassland soils that have been invaded by Virginia pine (Pinus virginiana Mill.). Sites representing three vegetation types (grassland, pine savanna, and pine woodland) were assessed at the Soldiers Delight Natural Environmental Area, Maryland, USA. In comparison to grassland sites, soil pH and concentrations of Ca, Mg, and Ni were reduced in pine woodland soils. Savanna soils exhibited an increase in Mg and Ni concentrations...

Molecular changes during chemical acidification of the buffalo and cow milks

Composition and physico-chemical properties of buffalo and cow milks were compared at their initial pH and during chemical acidification. As compare to cow milk, buffalo milk was richer in caseins and minerals such as Ca, Mg and Pi. Along with these differences, the capacity of buffalo milk to be acidified named buffering capacity was also higher than cow milk. The pH decrease induced aggregation of caseins at their isoelectric pH and solubilisations of Ca and Pi were significant for both milks. For both species, these molecular changes were qualitatively similar but quantitatively different. These differences suggested that the acidification process in dairy technology which is well established for cow milk can not be directly extrapolated to buffalo milk and some adaptations are necessary.

Effects of the 921 earthquake on the water quality in the upper stream at the Guandaushi experimental forest

A powerful 7.3 magnitude earthquake struck Taiwan on September 21, 1999. The stream water chemistry (pH, total alkalinity, conductivity, sodium, potassium, calcium, magnesium, ammonium, fluoride, chloride, sulfate, and nitrate) has been monitored since 1995 at the Guandaushi forestry riparian zone in central Taiwan. Collected data was used as a basis for comparing pre- and post-earthquake impacts. The pH, conductivity, and concentrations of Na, Ca, Mg, SO4, and HCO3 in stream water were lowest during the summer season, when stream water discharge was highest. On the other hand, the lowest concentrations of Cl, NH4, and NO3 in stream water occurred during the winter season, when stream water discharge was lowest. Also, K and F showed very little seasonal fluctuation in concentration. Downward trends in K and Ca were found 14 months prior to the earthquake; although, an upward trend occurred in NH4 at the same time.

The Effect of Fluoride at Plaque Fluid Concentrations on Enamel De- and Remineralisation at Low pH

The aim was to study the effect of fluoride, at concentrations typical of plaque fluid, on de- and remineralisation of subsurface lesions at low pH. Artificial lesions in human enamel were microradiographed to quantify mineral loss and placed in acid-gel systems at pH 4.8, 5.0 and 5.2. Calcium and phosphate were added to give initial Ca and Pi concentrations of either 4.1 and 8.0 mM, or 4.7 and 9.7 mM, at each pH value. Further, at each pH and combination of Ca and Pi, fluoride was added to the gels to give initial concentrations of 1, 2 or 5 ppm, with a non-fluoride control group. The lesions were removed after 10 days and change in mineral content quantified. Those in the non-fluoride control groups had demineralised further. Those exposed to fluoride had remineralised, the amount increasing with increasing fluoride concentration, up to a maximum value of approximately 75%. Calcium activity in the gels was reduced significantly, to levels similar to those reported for plaque fluid at low pH. Fluoride activity was also reduced, though to a lesser extent. These findings contrast with those from studies which have simulated conditions on smooth surface sites and which used experimental solutions composed to reflect salivary fluoride concentrations, where net demineralisation was observed at low pH. This reflects the need for further study of de- and remineralisation under plaque-fluid conditions. In conclusion, subsurface lesions were remineralised at low pH by fluoride at concentrations found in plaque fluid during a cariogenic challenge.

중금속으로 오염된 토양에서 분리한 중금속 내성 미생물의 수용액내 중금속 흡착

This study was conducted to find out a useful bioremediation technology for heavy metal contaminated soil and water. We isolated strain CPB from heavy metal contaminated soil and evaluated the tolerance level and adsorption capacity of strain CPB to heavy metals (Strain is not determined yet). Strain CPB showed variable tolerance limit to different kinds heavy metal or concentrations of heavy metals. The growth of strain CPB was significantly inhibited by mixed heavy metals (Cd+Cu+Pb+Zn) than that of by single heavy metal. Strain CPB showed high binding capacity with Pb (Pb>Cd>Cu>Zn). In general, strain CPB showed high uptake of heavy metals such as Pb, Cd and Cu. It was observed that the capacity of heavy metal uptake from mixture of heavy metals was reduced in comparison with single heavy metal treatment. But total contents of heavy metal bound with cell in mixed heavy metal showed higher than in single heavy metal treatment. Heavy metal adsorption in cells was affected by several external factors, such as temperature and pH etc.. The optimum temperature and pH of the adsorption of heavy metal into cells were ca. and pH ca. , respectively. A large number of the electron dense particles were found mainly on the cell wall and cell membrane fractions, which was determined by transmission electron microscope. Energy dispersive X-ray spectroscopy revealed that the electron dense particles were the heavy metal complexes the substances binding with heavy metals.

Forest vegetation as related to climate and soil conditions at varying altitudes on a humid subtropical mountain, Mount Emei, Sichuan, China

AbstractAltitudinal variations in temperature and soils were analysed on a humid subtropical mountain, Mt Emei (3,099 m a.s.l., 29°34.5′N, 103°21.5′E), in Sichuan, China, to see how the vegetation varies with the environmental factors. As a principal finding, the coldest mean monthly temperature −1°C, rather than the warmth index of 85°C·months, emerged as the primary factor that delimited the evergreen broadleaved forest. With regard to soils, properties such as organic C, total N, available P, exchangeable K tended to increase with altitude. The highest values in organic C (26.6%), total N (1.34%) and available P (45.39 ppm) were recorded in surface soils of the mixed forest (2,210 m a.s.l.) including all three tree life forms, i.e. evergreen/deciduous broadleaved and coniferous trees. The high pH and contents of exchangeable Ca and Mg in the surface soils derived from the parent material, limestone and dolomite, between 900 and 1,200 m, where several Tertiary tree species existed. The C/N ratios of surface soils in the coniferous forests (2,500–3,099 m) were higher than those of the evergreen broadleaved forests (600–1,500 m) and the mixed forests (1,500–2,500 m).

Cation channel activity of mucolipin-1: the effect of calcium

Mucolipidosis type IV (MLIV) is a rare, neurogenetic disorder characterized by developmental abnormalities of the brain, and impaired neurological, ophthalmological, and gastric function. Considered a lysosomal disease, MLIV is characterized by the accumulation of large vacuoles in various cell types. Recent evidence indicates that MLIV is caused by mutations in MCOLN1, the gene that encodes mucolipin-1 (ML1), a 65-kDa protein showing sequence homology and topological similarities with polycystin-2 and other transient receptor potential (TRP) channels. In this report, our observations on the channel properties of ML1, and molecular pathophysiology of MLIV are reviewed and expanded. Our studies have shown that ML1 is a multiple sub-conductance, non-selective cation channel. MLIV-causing mutations result in functional differences in the channel protein. In particular, the V446L and DeltaF408 mutations retain channel function but have interesting functional differences with regards to pH dependence and Ca(2+) transport. While the wild-type protein is inhibited by Ca(2+) transport, mutant ML1 is not. Atomic force microscopy imaging of ML1 channels shows that changes in pH modify the aggregation and size of the ML1 channels, which has an impact on vesicular fusogenesis. The new evidence provides support for a novel role of ML1 cation channels in vesicular acidification and normal endosomal function.

Amplified label-free electrocatalytic detection of DNA in the presence of calcium ions

A new label-free electrocatalytic method for the detection of DNA, is presented, in which DNA is the catalyst. The method takes advantage of the catalytic properties of the electrooxidised adenines within DNA toward the oxidation of NADH. This catalytic event results in an enhancement in the oxidation current of the electrooxidised adenines within DNA. Further improvement in this analytical signal is achieved in the presence of Ca(2+) ions. Parameters affecting the electrocatalytic current, such as pH or concentration of Ca(2+) ions have been investigated and optimised. Finally, the analytical features of the developed method are obtained. This method constitutes a more sensitive and reproducible alternative to other methods that use the oxidation current of the electrooxidised adenines without coupling to any catalytic event. A limit of detection of 33 fmol deoxyadenylic acid icosanucleotide (dA)(20), is obtained without labels.

Altered lung phospholipid metabolism in mice with targeted deletion of lysosomal-type phospholipase A2

Lung surfactant dipalmitoylphosphatidylcholine (DPPC) is endocytosed by alveolar epithelial cells and degraded by lysosomal-type phospholipase A2 (aiPLA2). This enzyme is identical to peroxiredoxin 6 (Prdx6), a bifunctional protein with PLA2 and GSH peroxidase activities. Lung phospholipid was studied in Prdx6 knockout (Prdx6-/-) mice. The normalized content of total phospholipid, phosphatidylcholine (PC), and disaturated phosphatidylcholine (DSPC) in bronchoalveolar lavage fluid, lung lamellar bodies, and lung homogenate was unchanged with age in wild-type mice but increased progressively in Prdx6-/- animals. Degradation of internalized [3H]DPPC in isolated mouse lungs after endotracheal instillation of unilamellar liposomes labeled with [3H]DPPC was significantly decreased at 2 h in Prdx6-/- mice (13.6 +/- 0.3% vs. 26.8 +/- 0.8% in the wild type), reflected by decreased dpm in the lysophosphatidylcholine and the unsaturated PC fractions. Incorporation of [14C]palmitate into DSPC at 24 h after intravenous injection was decreased by 73% in lamellar bodies and by 54% in alveolar lavage surfactant in Prdx6-/- mice, whereas incorporation of [3H]choline was decreased only slightly. Phospholipid metabolism in Prdx6-/- lungs was similar to that in wild-type lungs treated with MJ33, an inhibitor of aiPLA2 activity. These results confirm an important role for Prdx6 in lung surfactant DPPC degradation and synthesis by the reacylation pathway.

Visible, near infrared, mid infrared or combined diffuse reflectance spectroscopy for simultaneous assessment of various soil properties

Historically, our understanding of the soil and assessment of its quality and function has been gained through routine soil chemical and physical laboratory analysis. There is a global thrust towards the development of more time- and cost-efficient methodologies for soil analysis as there is a great demand for larger amounts of good quality, inexpensive soil data to be used in environmental monitoring, modelling and precision agriculture. Diffuse reflectance spectroscopy provides a good alternative that may be used to enhance or replace conventional methods of soil analysis, as it overcomes some of their limitations. Spectroscopy is rapid, timely, less expensive, non-destructive, straightforward and sometimes more accurate than conventional analysis. Furthermore, a single spectrum allows for simultaneous characterisation of various soil properties and the techniques are adaptable for ‘on-the-go’ field use. The aims of this paper are threefold: (i) determine the value of qualitative analysis in the visible (VIS) (400–700 nm), near infrared (NIR) (700–2500 nm) and mid infrared (MIR) (2500–25,000 nm); (ii) compare the simultaneous predictions of a number of different soil properties in each of these regions and the combined VIS–NIR–MIR to determine whether the combined information produces better predictions of soil properties than each of the individual regions; and (iii) deduce which of these regions may be best suited for simultaneous analysis of various soil properties. In this instance we implemented partial least-squares regression (PLSR) to construct calibration models, which were independently validated for the prediction of various soil properties from the soil spectra. The soil properties examined were soil pH Ca, pH w, lime requirement (LR), organic carbon (OC), clay, silt, sand, cation exchange capacity (CEC), exchangeable calcium (Ca), exchangeable aluminium (Al), nitrate–nitrogen (NO 3–N), available phosphorus (P Col), exchangeable potassium (K) and electrical conductivity (EC). Our results demonstrated the value of qualitative soil interpretations using the loading weight vectors from the PLSR decomposition. The MIR was more suitable than the VIS or NIR for this type of analysis due to the higher incidence spectral bands in this region as well as the higher intensity and specificity of the signal. Quantitatively, the accuracy of PLSR predictions in each of the VIS, NIR, MIR and VIS–NIR–MIR spectral regions varied considerably amongst properties. However, more accurate predictions were obtained using the MIR for pH, LR, OC, CEC, clay, silt and sand contents, P and EC. The NIR produced more accurate predictions for exchangeable Al and K than any of the ranges. There were only minor improvements in predictions of clay, silt and sand content using the combined VIS–NIR–MIR range. This work demonstrates the potential of diffuse reflectance spectroscopy using the VIS, NIR and MIR for more efficient soil analysis and the acquisition of soil information.

Changes in Concentrations of Major Elements and Trace Metals in Northeastern U.S.-Canadian Sub-Alpine Forest Floors

The forest floor at high elevation spruce-fir sites from southern Vermont, U.S. to the Gaspe Peninsula, Quebec, Canada was sampled and analyzed in 1979 and re-sampled and analyzed in 1996 to study temporal changes in the impacts of atmospheric pollutants. We determined organic matter mass, pH, and concentrations of Al, Ca, Fe, K, Mg, Na, Cd, Cu, Hg, Pb, and Zn for the litter (L = fresh litter plus Oi horizon) and fermentation plus humic horizons (F+H) (= Oe plus Oa horizons) of the forest floor. There were no trends for Al or Fe concentrations in the 1979 or 1996 L along the transect. Several sites had significantly lower Al and Fe values in 1996 than in 1979, likely indicating less mineral soil in the 1996 samples. The 1996 concentrations of Ca in L increased along the transect from 0.22% dry weight (dw) in Vermont to 0.60% dw in Quebec. Concentrations of Mg in L were relatively constant along the transect. Neither Ca nor Mg changed at sites from 1979 to 1996, indicating unchanged base status. Concentrations of Cd did not vary spatially along the transect but decreased at all sites from 1979 to 1996. Cu and Zn did not vary spatially or with time. In 1979, the concentration of Hg in L ranged between 150 and 300 μg kg−1 dw, with no spatial gradient. By 1996, Hg concentrations were 25 to 50% lower in L, with decreases generally proportional to the concentration in 1979. The concentration of Pb in 1979 L decreased significantly from 200 mg kg−1 dw in southern Vermont to 60 mg kg−1 dw in Quebec. By 1996, the Pb concentration in L ranged between 32 and 66 mg kg−1 dw with no spatial trend along the transect. Decreases in Pb concentrations at sites were proportional to the absolute value in 1979. The concentrations of Cd, Hg, and Pb have declined in litter from 1979 to 1996, indicating a decline in atmospheric deposition. Higher Hg and Pb accumulation rates to the southwest are suggested for the past as indicated by (F+H) concentrations and inventories of Hg and Pb. The decline of Pb in L is consistent with the decreased use of leaded gasoline starting in the 1970s; the declines in Cd and Hg probably reflect lower emissions over the same period. Declining concentrations of Cd, Hg, and Pb in L parallel those documented in recent lake and peat sediments in the northeastern United States.

Peatlands and green frogs: A relationship regulated by acidity?

:The effects of site acidification on amphibian populations have been thoroughly addressed in the last decades. However, amphibians in naturally acidic environments, such as peatlands facing pressure from the peat mining industry, have received little attention. Through two field studies and an experiment, I assessed the use of bog habitats by the green frog (Rana clamitans melanota), a species sensitive to various forestry and peat mining disturbances. First, I compared the occurrence and breeding patterns of frogs in bog and upland ponds. I then evaluated frog movements between forest and bog habitats to determine whether they corresponded to breeding or postbreeding movements. Finally, I investigated, through a field experiment, the value of bogs as rehydrating areas for amphibians by offering living Sphagnum moss and two media associated with uplands (i.e., water with pH ca 6.5 and water-saturated soil) to acutely dehydrated frogs. Green frog reproduction at bog ponds was a rare event, and no net movements occurred between forest and bog habitats. However, acutely dehydrated frogs did not avoid Sphagnum. Results show that although green frogs rarely breed in bogs and do not move en masse between forest and bog habitats, they do not avoid bog substrates for rehydrating, despite their acidity. Thus, bogs offer viable summering habitat to amphibians, which highlights the value of these threatened environments in terrestrial amphibian ecology.

알긴산칼슘 비드 상 흡착에 의한 흔적량 구리(II)와 납(II)의 동시 농축 및 정량

Department of Chemical Engineering, Samcheok National University, Samcheok, Gangwon 245-711, Korea(Received October 11, 2004) . Cu(II) Pb(II) . Ca(II) . pH, Ca(II) , , , . Cu(II) Pb(II) Ca(II) pH 5.0 , . , . , 1.0 mol/L . Na(I), K(I) Mg(II) Pb(II) Cu(II) . 2 90.4~104.3% Cu(II) Pb(II) . : , , , (II), (II)ABSTRACT. The preconcentration and determination of trace Cu(II) and Pb(II) on calcium alginate beads in aqueous solu-tion were studied. A calcium alginate beads were prepared by adding an alginic acid to sample solution contained Ca(II). Somefollowing conditions were optimized: the pH of sample solution, amount of alginic acid, and stirring time for effective adsorp-tion; the type and concentration of acid, and sonication time in an ultrasonic vibrator for the perfect de-sorption. A sample solu-tion was prepared with Cu(II) and Pb(II) in DI water. And Ca(II) and ethanol was added into the sample solution. The pH ofthe final sample solution was controlled with buffer solution. The alginic acid were dispersed in the sample solution by a mag-netic stirrer. This mixture was stored in room temperature for 30 min to form a calcium alginate. After the beads were filteredand washed on a membrane filter, the analytes were redissolved from the beads by an ultrasonic vibration of 10 minutes in 1.0MHNO

Liberação de cálcio e magnésio por cápsulas porosas de porcelana usadas na extração de solução do solo

O uso de cápsulas porosas para extração de solução do solo é interessante por ser um ensaio não-destrutivo. Entretanto, persistem dúvidas sobre a liberação de íons da própria cápsula, que podem contaminar a solução extraída. Foram realizados testes na Faculdade de Ciências Agronômicas/UNESP, Botucatu (SP), com o objetivo de verificar a liberação de Ca e de Mg por cápsulas porosas de porcelana. No primeiro, foram empregados quatro tratamentos: T1 - lavagem das cápsulas com água destilada, forçando sua passagem pelas cápsulas, utilizando uma bomba a vácuo; T2 - lavagem das cápsulas com HCl 0,1 mol L-1, forçando sua passagem pelas cápsulas, utilizando uma bomba a vácuo; T3 - lavagem das cápsulas com água destilada, sem vácuo, e T4 - lavagem das cápsulas com HCl 0,1 mol L-1, sem vácuo, em um tempo de imersão de 24 h (para T3 e T4). No segundo teste, as cápsulas tratadas com HCl 0,1 mol L-1 no primeiro teste foram lavadas com água destilada novamente e deixadas de molho em água destilada e deionizada durante 45 min. Após estes procedimentos, as cápsulas foram imersas em água destilada, tomando-se alícotas desta solução para determinação de pH e dos teores de Ca e Mg após contato com as cápsulas por 0; 0,5; 1,0; 2,0; 4,0 e 24 h. Cada tratamento teve quatro repetições. Não se observou liberação significativa de Ca e Mg das cápsulas porosas para a solução, quando foram preparadas utilizando-se da passagem de HCl 0,1 mol L-1 a vácuo e água destilada, e deixadas, a seguir, em água destilada e deionizada durante 4 h.

Response of wheat, triticale and barley to lime application in semi-arid soils

Field experiments were conducted on four acid soils which were typical of the eastern section of the cropping region in southeastern Australia. The response of three cereal varieties to application of limestone or elemental S was measured as a function of soil pH. The cereals were selected to cover the known range of tolerance to acidity: Triticale ( × Triticosecale wittmack cv. Currency) (tolerant); wheat ( Tritcum aestivum cv. Matong) (moderately tolerant) and barley ( Hordeum vulgare cv. Schooner) (sensitive). A two asymptote logistic equation was used to describe the relationship between soil pH and rates of limestone and elemental sulphur. The upper asymptotes for the four sites were well below the pH of lime saturation as the agriculturally practiced rates of lime were lower than the rates that could achieve the maximum pH in the field. The same equation was used to fit higher rates of lime application to a similar soil type to one of the four sites in this study and resulted in an upper asymptote of 7.26. Crop yield responses to lime application were well described by soil pH Ca (0.01 M CaCl 2). Soil pH Ca ranges which gave 95% of maximum yield were pH Ca 4.3–5.6 for Matong wheat, 4.4–4.8 for Currency triticale and 4.7–5.8 for Schooner barley. It was found that rainfall played an important role in limiting the yield response of crops to lime application. Lime reaction, lime requirement and grain yield models should include rainfall and soil water content as these influence the rate and extent of dissolution of limestone and subsequent plant response in a semi-arid environment.

Manejo da calagem e os componentes da acidez de Latossolo Bruno em plantio direto

A viabilidade da aplicação de calcário sobre a superfície de solos em plantio direto e seu efeito na acidez em subsuperfície são pouco conhecidos. O presente estudo foi realizado em experimento de longa duração (21 anos), instalado, em 1978, em Guarapuava (PR), e teve por objetivo avaliar o efeito do método de reaplicação de calcário nos componentes da acidez das fases sólida e líquida de um Latossolo Bruno alumínico em plantio direto. Os tratamentos avaliados foram: sem calcário, calcário incorporado por uma lavração e duas gradagens e calcário aplicado sobre a superfície do solo, sem incorporação. Reaplicações de calcário foram realizadas em 1987 e 1995 nas doses de 4,5 e 3,0 Mg ha-1 de calcário, respectivamente. A amostragem de solo foi feita manualmente, em abril de 1999, em nove camadas até 0,4 m de profundidade. A reaplicação de calcário promoveu melhoria no ambiente químico do solo em plantio direto, evidenciada pela elevação do pH em água, dos teores de Ca e Mg trocáveis e em solução, da saturação por bases, bem como pela diminuição dos teores de Al trocável. A aplicação de calcário sobre a superfície do solo em plantio direto foi eficiente na elevação do pH na camada de 0-0,15 m e na elevação dos teores de Ca e Mg trocáveis e da saturação por bases, bem como na diminuição dos teores de Al trocável na camada de 0-0,20 m, não diferindo do tratamento com incorporação de calcário ao solo. A eficiência da calagem superficial na correção da acidez da camada arável do solo constitui importante indicativo da viabilidade desta prática em solos sob plantio direto de longa duração.

Effect of Diamou Lime, Gypsum, and Tilemsi Phosphate Rock on Acid Soils of the Sudano-Sahelian Region of Mali

Continuous cropping, use of chemical fertilizers, and lack of sound soil management practices on poorly buffered kaolinitic Alfisols of the Sahel have accelerated soil acidity and reduced exchangeable Ca and crop yield. This study was conducted at the Cinzana Experiment Station in Mali, to determine the relative importance of Ca and P for millet grown on Plinthustalf sandy and Haplustet clayey soils for three years. The soils selected had very low to medium Bray P1 and extractable Ca concentrations. Three local sources of Ca and one source of P, Diamou lime, gypsum, and Tilemsi phosphate rock (TPR) were surface applied at lime application(LA) of 0, 0.5, 1.0, and 2.0 CaCO3equivalent. Among the three Ca sources, Diamou lime increased pH and exchangeable Ca concentration of surface soil, TPR increased the Ca concentration in the surface soil, and gypsum increased the Ca concentration of both surface and subsurface soil, but like TPR had no effect on soil surface or subsurface pH. The degree of millet yield response to Ca source varied with soil and year. No response to Ca was observed in a low rainfall year, but a positive response to TPR occurred in all three years, regardless of rainfall. For the soils studied, TPR can be considered a good local source of Ca and P, with potential to reduce Al toxicity and/or Ca deficiency. In general, application of P was more critical than Ca for millet growth in these soils.