Low Electrical Conductivity Values Research Articles

Numerical optimization of the spatial conductivity distribution within cathode microstructures of lithium-ion batteries considering the cell performance

Summary A numerical approach targeting the optimization of the spatial conductivity distribution within a three-dimensional electrode microstructure of lithium-ion batteries is presented. Its methodology is based on a spatially resolved three-dimensional electrochemical model of a lithium-ion battery half cell on the particle scale. Although being independent of the underlying electrode microstructure, the method is exemplarily applied on a computer-generated periodic electrode structure consisting of smooth spherical particles. In the first step, parameter variations are performed to investigate the influence of the electrical conductivity on the simulated half-cell performance. The simulations show that the performance-limiting effect of low electrical conductivity values can be attributed to a through-plane directed inhomogeneity of the local intercalation flux density. Furthermore, it is shown that if a homogenous surface intercalation flux density is reached, a further increase of the spatially uniform conductivity would not result in better half-cell performance. In the second step, the determined optimum spatially uniform conductivity value is taken as a basis for the spatial optimization approach. The resulting conductive structure within the electrode shows gradient-like behavior directed perpendicular to the electrode surface, while highest conductivity values are to be expected in the region close to the current collector. Therefore, multiple layer coating is suggested as a suitable practical manufacturing approach. Due to the proposed two-stage optimization approach, the resulting conductive structure reveals conductivity saving potential without altering the macroscopic cell performance.

Origin and mechanisms of high salinity in Hombolo Dam and groundwater in Dodoma municipality Tanzania, revealed

The Hombolo dam (HD), in central Tanzania, is a shallow reservoir characterized by high salinity that limits its use for human activities. The origin of the salinity, mechanisms of reaching and concentrating in the dam remain unclear. These were assessed using hydrogeochemical facies, water type evolutions and mapping. The source of HD salinity was identified to be shallow groundwater (SG) and runoff from a seasonal floodplain with NaCl-rich lithological materails, along Little Kinyasungwe River that feeds the dam. The NaCl-rich lithological units, about 5–7 km upstream of the dam, were highly concentrated with NaCl to the extent that the local community was commercially separating table salt from them. The physicochemical parameters from these NaCl-rich lithological materials were well represented in HD and nearby groundwater sources, which suggests active water interactions. Water type evolution and surface hydrology assessments clearly showed that SG in the salty-floodplain was influenced by evaporation (ET) and was periodically carried to the HD. Clearly; HD water had high chemical similarity with the nearby SG. This agrees with previous studies that HD is partly fed by the local aquifer. However, this is the first attempt at mapping its physical origin. The origin of HD salinity was further supported by the spatial distribution of electrical conductivity (EC), where very high EC (up to 21,230 μScm−1) was recorded in SG within the NaCl-rich lithological unit while water sources far away from the NaCl-rich materials had much lower EC values. Thus, the study disagrees with previous conclusions that HD salinity was sorely due to high dam surface ET but is primarily due to geological reasons. Comparisons of HD with a nearby Matumbulu dam (MD), another earthen dam in climatologically similar settings, reveals that MD water was less saline/mineralised. This further shows that HD high salinity is most likely a geologic phenomenon, but local climatic factors, namely high ET, decreasing rainfall and warming trends are likely to have concentrated the salts further. Although HD is widely/ideally used for grape vine irrigation, it was clearly revealed that its prolonged usage would potentially affect the soil and grape productivity due to high salinity.

Vegetation establishment on ‘Green Walls’: Integrating shotcrete walls from road construction into the landscape

The establishment of a sustainable vegetation layer on shotcrete walls subjected to road environment represents enormous challenges. High inclination of almost 90°, the exposed position of the walls near streets as well as lack of soil and water supply pose major limiting conditions. The objective of this study was to evaluate the performance of an innovative greening technology for vertical structures in terms of vegetation development on varying plant substrates and geotextiles.The field experiment included testing three plant substrates on basis of nearby rocky excavation material (‘Innsbrucker Quarzphyllit’, ‘Bündnerschiefer’ and ‘Zentralgneis’) combined with compost. Additionally, five geotextiles (geogrid (3x4 mm), geogrid (9x10 mm), coir net, coir mat, geo mat) were applied for assessment. All test combinations were evaluated regarding vegetation cover, species composition, and biomass production from 2015 to 2016. Analyses of chemical properties were conducted for all plant substrates.Results showed highest vegetation cover ratio on ‘Bündnerschiefer’ and ‘Innsbrucker Quarzphyllit’, which can be explained by the favorable mineral composition (nutrient storage capacity) and chemical properties of compost (lower values of electrical conductivity and C/N ratio).In conclusion, the use of ‘Green Walls’ filled with ‘Bündnerschiefer’ or ‘Innsbrucker Quarzphyllit’ plant substrate in combination with netlike geotextiles like geogrid or coir net proved best. They are promising in terms of establishing an optimal vegetation cover on vertical structures and are well suited for integrating shotcrete walls into the landscape. The use of local excavation material for greening purposes thus can be confirmed. Though, the use of high-quality compost is crucial.

Hypothesis of Groundwater Flow through Geological Structures in Guarani Aquifer System (GAS) using Chemical and Isotopic Data

Guarani Aquifer System (GAS) is one of the most important in South America shared by more than 9 million people living in Argentina, Brazil, Paraguay and Uruguay. Groundwater flow through GAS is controlled by the geological framework of the Paraná and Chacoparanense sedimentary basins, dividing the aquifer in four groundwater flow compartments. The limit between north and southern compartment of the GAS is represented by the Rio Grande-Asunción Arch (RGAA), a megastructure that represents a regional uplift. During long time the role played by this important geological structure over groundwater flow has remained a controversial question. Groundwater from the northern portion of the RGAA is characterized by elevated values of electrical conductivity (.>1,500 μS.cm-1), Na-Cl-SO4 type, and oversaturated with respect to calcite. On the other hand, despite their downgradient position, samples collected south of the structure, present low values of electrical conductivity (300-500 μS.cm-1), Ca-HCO3 or Na-HCO3 types, and most samples are not saturated with respect to calcite. These differences allow inferring that groundwater flow through RGAA would not have continuity. Moreover, an important recharge zone could be stablished along the structure, partially responsible for the replenishment of the GAS in the southern compartment.

Assessing Nutrient, Biomass, and Sediment Transport of Drainage Ditches in the Three Gorges Reservoir Area

The contributions of drainage ditches to the accelerated eutrophication of rivers have rarely been assessed, especially for the Three Gorges Reservoir (TGR) drainage ditches. Forty drainage ditches in the TGR from multiple land use types were extensively investigated for 10 parameters of water quality. The results showed that the concentrations of total nitrogen (TN) and total phosphorus (TP) in the TGR drainage ditches were generally far higher than the internationally recognized eutrophication threshold. Based on this study, both ditch water and sediments from residential land and roadside land had the highest concentrations of nutrients. Possible sources of these nutrients include sewage water and septic tank overflow. Forestland had significantly lower concentrations of nutrients. Residential ditches had higher values of electrical conductivity (EC) and total dissolved solid (TDS) values and lower dissolved oxygen (DO) concentrations. Forestland had lower values of EC and TDS values and higher DO concentrations. The results indicate that the nutrients that have accumulated in the sediments have significant impacts on the water quality in adjacent ditches. A long‐term plan must be developed to more strictly control the external loading of nutrients from surrounding land. Action plans to promote the growth of wetland plants in drainage ditches are important for increasing agrochemical retention in the TGR drainage ditches. TGR drainage ditches from residential zones must be actively managed by cleaning and sediment removal to control the risk of nutrients being released into the reservoir.

Nutrient removal in a trapezoidal vegetated drainage ditch used to treat primary domestic sewage in a small catchment of the upper Yangtze River

AbstractA trapezoidal constructed ditch (TCD) of 300 m length and 2.2 m width was designed and built in the downstream section of the upper Yangtze River for in situ treatment of primary domestic sewage. The removal efficiencies of TN, NH4‐N, NO3‐N, TP and PO4‐P from the TCD were approximately 61, 63, 48, 58 and 51%, respectively. The concentrations of TN, NH4‐N, NO3‐N, TP and PO4‐P showed a decreasing trend with increasing distance downstream. Plant assimilation and sediment retention were the key mechanisms for N and P removal within the TCD, with subsequent microbial uptake and transformation of the nutrients. The TCD outlet showed significantly higher dissolved oxygen (DO) concentrations and lower values of electrical conductivity and total dissolved solids compared to the influent. Results of this study highlight the potential of TCD to mitigate nutrients from primary domestic sewage transported downstream and could be incorporated into local best management practices.

Edaphic factors controlling the distribution of inland halophytes in an ephemeral salt lake “Sabkha ecosystem” at North African semi-arid lands

This study aims to characterize soil properties and to investigate how these parameters, including soil salinity, are related to zonation and distributional patterns of halophytic plants occurring at edges of the Djendli Sabkha (northeastern Algeria). Soil samples were collected from four stations at Sabkha edges with seven samples for each station. Physicochemical soil parameters were analysed in each vegetation belt of halophytes. Relationships between soil traits were tested to determine spatial variation and their effects on vegetation cover of the principal halophyte species. The influence of pedological factors on the distribution and establishment of halophytes was considered using a redundancy analysis (RDA) and generalized linear models. Positive correlations were found between organic matter, carbon and nitrogen which were negatively correlated with electrical conductivity (EC), pH, gypsum, Na+ and Cl− concentrations. Sharp limits were found between halophyte communities even though there is a gradual change in the physicochemical environment along the gradient centre-to-edge of the Sabkha. RDA showed that edaphic variables that best explained the data were EC, pH, organic matter (OM), carbon and nitrogen contents, Na+ and Cl− concentrations. Sarcocornia fruticosa grew under higher soil salinity (EC=7.2–13.8dS/m) compared to Suaeda fruticosa and Suaeda vermiculata that afford moderate soil salinity, than Atriplex halimus established in soils with low EC values (5.5–7.3dS/m) but with high values of OM, carbon and nitrogen contents and low values of Na+, Cl− and pH. Sarcocornia fruticosa grew in soils characterized with high pH, Na+, Cl− values but relatively low in OM, carbon and nitrogen contents.

Synthesis and preliminary study of the double perovskite NdBaMn2O5 + δ as symmetric SOFC electrode material

NdBaMn2O5+δ compound has been studied as a possible symmetric SOFC electrode. The A-site and charge ordered NdBaMn2O5 material has been synthesized by solid-state reaction in a reducing atmosphere at 1100°C for 12h; the resulting material crystallizes in a 2ap×ap×2ap tetragonal cell of P4/nmm space group. Thermogravimetric analysis coupled to HT-XRD experiment shows that the material is completely stable to redox cycling between air and 5% H2/Ar up to at least 850°C. In air, the phase is completely oxidized to A-site ordered NdBaMn2O6 (P4/mmm) and in anode conditions is reduced back to its initial form, with intermediate formation of orthorhombic NdBaMn2O5.5 ordered phase. Considering possible conditions of cell preparation in air (T=1300°C for 6h), a loss of A-site ordering is evidenced but the material is reduced back to ordered NdBaMn2O5 at 850°C in diluted hydrogen. Whereas the material reacts strongly with 8YSZ at 1300°C, no particular chemical affinity with 20GDC is observed neither at high temperature in air nor at 850°C in anodic atmosphere; TEC coefficients for NdBaMn2O5+δ, measured in both anode and cathode conditions, are also in good agreement with reported TEC values for a ceria electrolyte. Relatively low values of electrical conductivity are found in diluted hydrogen whereas a sufficient level for the application is obtained in air.

Evaluation of the use of treated municipal waste water on the yield, oil quality, free fatty acids’ profile and nutrient levels in olive trees cv Koroneiki, in Greece

Tertiary reclaimed municipal wastewater was used in order to assess its effectiveness in irrigating olive trees cv Koroneiki against fresh water (FW), for two consecutive cultivating periods. A total of 140 olive trees were used and olive production, oil quality, oil free fatty acid profile and olive nutrition were assessed. The treated municipal wastewater (TMW) used was characterized by relatively low electrical conductivity values, still higher than the FW and higher NH4, Cl, K, Na, Fe, B, Al and Mn concentration than FW. The application of TMW slightly increased fruit production during the year of high tree yield (15.92kg fruit per tree versus 12.73kg per tree under FW irrigation) as well as the oil content, during the year of low yield (18.21% versus 16.43% under FW irrigation). It did not have any significant effect on the oil quality characteristics, such as free acidity, K270, K232, peroxide value and Delta K index. The irrigation treatment did not have any significant effect on the free fatty acid profile of the oil. Oleic acid was the dominant free fatty acid in the oil (ranging from 77.7 to 78.6%), followed by palmitic (10.6–11.1%), linoleic (5.5–5.8%) and stearic acid (2.5–2.8%), with their concentration falling within the range of the values for characterizing it as “Extra virgin” olive oil. The levels of K, Ca, Mg, Mn, Fe and Zn in the leaves increased with the application of TMW compared to FW, while the continuous use of TMW for two years led to a significant increase of P, Mg, Fe, Mn and Zn levels. The use of TMW under the experimental conditions described in the present study could be a valuable and profitable alternative to the use of FW in short term, by improving tree nutritional condition and enhancing oil production of superior quality.

Spatial distribution of bowal and differences in physicochemical characteristics between bowal and woodland soils in Benin, West Africa

Bowal, is degraded land surface characterized by ferricrete exposure due to soil surface erosion. This study aims at assessing the spatial distribution of bowé in Benin and the physicochemical differences between bowé and soil of adjacent woodlands. Bowé surfaces were identified during field investigations and mapped. Soil samples were taken on the bowé surfaces and nearby woodland. Mann–Whitney test was applied to analyze the different physicochemical characteristics of bowé and woodland. The results show that bowé were directly related to ferruginous soils and rainfall regime. Bowé soils are characterized by significantly lower values of electrical conductivity, organic matter, extractable phosphorus, silt and total nitrogen than woodland soils, while potassium exchangeability of bowé soils is higher. Bowé can be expected wherever ferruginous soils and/or ferricretes are observed under unimodal rainfall regimes condition. The disaggregation of bowé ferricretes may improve the soil physicochemical characteristics and sustain the regrowth of forest under more humid conditions.

Pristine aquatic systems in a Long Term Ecological Research (LTER) site of the Brazilian Cerrado.

The maintenance of limnological monitoring programs in the Cerrado Domain is crucial as a provision of useful information about temporal variations in land use and their respective water quality responses, considering its importance as water source for different Brazilian hydrographic basins. The purpose of this research was to describe limnological variables of low-order lotic systems located in the Cerrado Long Term Ecological Research (LTER) site (Environmental Protection Area (APA) Gama and Cabeça de Veado, Federal District of Brazil). Altogether, nine different streams were considered in this study. Samplings were conducted between 2010 and 2012, concentrated in the dry and rainy seasons. The sampling sites were generally characterized by low nutrient concentrations (e.g., medians, TP = 14.8μgL(-1), TN = 20.0μgL(-1), NO3 = 13.8μgL(-1)) and slightly acidic waters (median, pH = 5.3), with quite low electrical conductivity values (median = 6.4μScm(-1)). However, water quality degradation as a response to diffuse pollution was reported in some sampling points (e.g., Onça and Gama streams), expressed by relatively higher N and P concentrations, which were probably highlighted by the good water quality of the data set as whole. Although there was a trend to higher values of nitrogen forms during the dry season, significant statistical differences between the seasonal periods were reported only for the variables temperature and dissolved silica, which were higher in the dry and rainy season, respectively. The streams located in the preserved areas inside the ecological stations of APA Gama and Cabeça de Veado can still be considered good examples of reference lotic systems in the Cerrado Domain; notwithstanding, this study reported incipient signs of water quality degradation which cannot be overlooked in future limnological monitoring.

Using hydrochemical tracers to assess impacts of unsewered urban catchments on hydrochemistry and nutrients in groundwater

AbstractWe applied graphical methods and multivariate statistics to understand impacts of an unsewered slum catchment on nutrients and hydrochemistry of groundwater in Kampala, Uganda. Data were collected from 56 springs (groundwater), 22 surface water sites and 13 rain samples. Groundwater was acidic and dominated by Na, Cl and NO3. These ions were strongly correlated, indicating pollution originating from wastewater infiltration from on‐site sanitation systems. Results also showed that rain, which was acidic, impacted on groundwater chemistry. Using Q‐mode hierarchical cluster analysis, we identified three distinct water quality groups. The first group had springs dominated by Ca‐Cl‐NO3, low values of electrical conductivity (EC), pH and cations, and relatively high NO3 values. These springs were shown to have originated from the acidic rains because their chemistry closely corresponded to ion concentrations that would occur from rainfall recharge, which was around 3.3 times concentrated by evaporation. The second group had springs dominated by Na‐K‐Cl‐NO3 and Ca‐Cl‐NO3, low pH but with higher values of EC, NO3 and cations. We interpreted these as groundwater affected by both acid rain and infiltration of wastewater from urban areas. The third group had the highest EC values (average of 688 μS/cm), low pH and very high concentrations of NO3 (average of 2.15 mmol/l) and cations. Since these springs were all located in slum areas, we interpreted them as groundwater affected by infiltration of wastewater from poorly sanitized slums areas. Surface water was slightly reducing and eutrophic because of wastewater effluents, but the contribution of groundwater to nutrients in surface water was minimal because o‐PO4 was absent, whereas NO3 was lost by denitification. Our findings suggest that groundwater chemistry in the catchment is strongly influenced by anthropogenic inputs derived from nitrogen‐containing rains and domestic wastewater. Copyright © 2013 John Wiley & Sons, Ltd.

Electrical and Thermal Characterization of Electrospun PVP Nanocomposite Fibers

Polyvinylpyrrolidone (PVP) solutions incorporated with multiwall carbon nanotubes (MWCNTs) were electrospun at various weight percentages, and then the electrical resistance and some thermal properties of these nanocomposite fibers were determined using a high‐accuracy electrical resistance measurement device. During the electrospinning process, system and process parameters, such as concentrations, applied voltage, tip‐to‐collector distance, and pump speeds, were optimized to receive the consistent nanocomposite fibers. When polymers are used in many industrial applications, they require high electrical and thermal conductivities. Most polymers exhibit low electrical conductivity values; however, in the presence of conductive inclusions, the electrical resistance of the MWCNT fibers was reduced from 50 MΩ to below 5 MΩ, which may be attributed to the higher electrical conductivities of these nanoscale inclusions and fewer voids under the applied loads. This study may open up new possibilities in the field for developing electrically conductive novel nanomaterials and devices for various scientific and technological applications.

Influence of oxide scale thickness on electrical conductivity of coated AISI 430 steel for use as interconnect in solid oxide fuel cells

The use of conductive coating on interconnect ferritic stainless steel can reduce electrical resistivity. In this study, an AISI 430 ferritic stainless steel interconnect was coated with a manganese base pack mixture by pack cementation. The effect of oxide scale thickness on electrical conductivity was evaluated by applying isothermal oxidation at 750 °C. This effect was also investigated at different temperatures (400–900 °C). The formation of manganese spinels during annealing improved the oxidation resistance and electrical conductivity. Results showed that the increase in isothermal oxidation time and temperature increased the oxide thickness, and this resulted in the relatively low values of electrical conductivity. Manganese spinels enhanced the electrical conductivity and oxidation resistance of coated substrates as compared to uncoated substrates.

Relación entre la conductividad eléctrica, pH del agua de remojo, germinación de semillas y crecimiento de plántulas de maíz (Zea mayz L.) bajo dos condiciones experimentales

Corn (Zea mayz L.) seeds of twelve lots of different acquisition years were used to study the relation among the measurements of electrical conductivity (EC) and pH of the soaking water and the germination in laboratory, under normal conditions (NC) and accelerated aging (AA) of seeds. A randomized complete block design was used with four replications, an analysis of variance was applied and differences among seed lots were detected by Least Significant Difference Test. Seed lots showed high percentage of germination at eight days of evaluation in (NC) and the unfavorable effect of AA was demonstrated. Dry shoot and radicle weights showed significant differences among the lots. Values of EC were related to percentage of germination in laboratory under AA. Seed lots that showed high percentage of germination in laboratory, previous AA, presented low values of electrical conductivity, therefore, this test could be good indicative of the behavior of corn seeds under extreme or unfavorable conditions of germination. The test of pH did not show direct relation with the seed emergency in laboratory.

Esterco de gado leiteiro associado à adubação mineral e sua influência na fertilidade de um latossolo sob plantio direto

A produção de gado de leiteiro no sul do Brasil ocorre em grande parte em sistema de semi ou completo confinamento dos animais, o que gera uma produção significativa de resíduos. Os resíduos gerados vêm sendo utilizados como única fonte de nutrientes ou associados a fontes minerais na produção de grãos e silagem, mas sua influência nas características de solo não tem sido bem caracterizada. Este trabalho foi realizado com o objetivo de avaliar a influência de doses de adubação com esterco líquido de gado leiteiro, associadas com adubação mineral, sobre os níveis de P, K, C e condutividade elétrica (CE) de um Latossolo Bruno, em sistema plantio direto e rotação de culturas de inverno e verão (sorgo/aveia-preta/milho/azevém/milho/azevém), para produção de silagem, nas camadas de 0-5, 5-10, 10-30, 30-50 e 50-80 cm de profundidade. Os tratamentos foram distribuídos em três blocos casualizados, divididos em 12 parcelas cada bloco, em arranjo fatorial 3 x 4, sendo três níveis de adubação mineral (0, 50 e 100 % da dose recomendada para as culturas) e quatro níveis de adubação orgânica (0, 30, 60 e 90 m³ ha-1 ano-1). A adubação mineral proporcionou maiores valores de P disponível (Mehlich-1 e resina) até a profundidade de 10 cm, dada a adição em profundidade pela plantadeira, enquanto, com esterco aplicado em superfície, os maiores valores ficaram restritos à profundidade de 0-5 cm. Constatou-se esgotamento de K ao longo do perfil devido à elevada extração via silagem, tendo o esterco líquido aplicado uma relação linear com teor de K disponível, em todas as profundidades analisadas. A ausência de efeito da adubação mineral sobre o K deve-se, provavelmente, à baixa dose de K adicionada. Foi observada relação direta entre doses de esterco e teores de C orgânico na camada de 0-5 cm, o mesmo não sendo observado quando do uso de adubo mineral. Baixos valores de CE sugerem grande exportação de nutrientes pela produção de silagem. Os resultados obtidos indicam que não houve movimentação significativa de P no perfil do Latossolo, mesmo após seis anos sob altas doses de esterco de gado leiteiro, e que o K aplicado via esterco e adubação mineral não é suficiente para manter os níveis deste nutriente em sistemas em que a extração de K pela silagem é alta. Nessas situações, o aumento dos teores de C orgânico é restrito à camada superficial do solo em plantio direto e diretamente relacionado com a dose de esterco aplicada.

INFLUENCE OF PRIMING TREATMENTS ON VIGOUR AND VIABILITY OF PAPAYA SEEDS

Seed invigouration studies in papaya (Carica papaya L.) were conducted at CCS Haryana Agricultural University, Hisar, Haryana, India, with the objective to identify suitable priming treatments for freshly extracted and aged seeds. Priming treatments consisted of hydration, 500 ppm GA 3 , 1000 ppm GA 3 , 0.5 M KNO 3 , 1 M KNO 3 0.5 M thiourea, 1 M thiourea and untreated fresh seeds (control). The fresh and 24 h accelerated aged seeds treated with 1000 ppm GA 3 showed significantly the highest germination percentage. The freshly extracted seeds of all the seed lots when treated with 1000 ppm GA 3 exhibited maximum seedling length followed by 500 ppm GA 3 . Similar trends were observed in case of accelerated aged seeds at 24 and 48 h. The fresh seeds and accelerated aged seeds at 24 and 48 h exhibited higher dry weight for seedlings. The fresh seeds treated with 1000 ppm GA 3 exhibited significantly higher vigour indices (I and II) than other priming treatments. The vigour indices of fresh seeds were significantly higher than the accelerated aged seeds. In 24 h accelerated aged seeds, 1000 ppm GA 3 showed significantly higher vigour indices-I and II in seed lots. In fresh seeds, priming treatment with 1000 ppm GA 3 gave significantly higher viability percentage while in 24 h aged seeds, 0.5 M KNO 3 and 1000 ppm GA 3 treatments gave significantly higher viability percentage. In fresh seeds, treatment with 1000 ppm and 500 ppm GA 3 gave significantly lower values of electrical conductivity in all the seed lots. The trend was also visible in 24 and 48 h accelerated aged seeds. Priming treatment with 1000 ppm GA 3 exhibited significantly the highest dehydrogenase activity besides it was also higher with 24 and 48 h accelerated aged seeds.

Osmotic and ionic effects of various electrolytes on the growth of wheat

Pot experiments were conducted using a sandy loam soil and various electrolyte solutions such as NaCl, CaCl2, Na2SO4, and Hoagland nutrient solution containing all macro- and micro-nutrient elements in appropriate proportions, inducing different electrical conductivity (EC) levels of the soil solution during the growth of Krichauff wheat while the water content in the pot soils was maintained at field capacity. The resulting differences in dry matter production after 40 days of growth clearly indicated the continuous operation of osmotic effect as the EC of the soil solution increased from 0.7 to 41.0 dS/m. However, the osmotic effect became dominant and severely restricted plant growth when the soil solution EC increased above a ‘threshold value’, which was 25 dS/m, corresponding to an osmotic pressure of 900 kPa, in this experiment. Below this EC value, particularly at low EC values, ionic effects due to Na+, Ca2+, SO42–, and Cl– were also evident, but it could not be concluded whether these effects were due to toxicity or ion imbalance. The osmotic effect at EC values above the threshold resulted in greatly reduced water uptake from pot soils, the unused water being in the range 89–96% of the field capacity of the soil. Water use efficiency is a major factor in profitable and sustainable dryland agriculture. Both soil management and selection and breeding of salt-tolerant plants should concentrate on ensuring that the threshold EC value for severe osmotic effects is not reached under field conditions.

Effects of sunflower ( Helianthus annuus L .) extracts on wheat ( Triticum aestivum L .) and physicochemical characteristics of soil

Pot-grown seedlings of wheat cultivars Margalla 99 and Chakwall 97 were given water mixed with extracts of sunflower leaves, stems, or roots 20 days after the seedlings had emerged. Data on growth and yield parameters, weed density, and hormone production were recorded. Physicochemical properties of soil were analysed before sowing sunflower and after harvesting wheat. Commonly observed effects of allelochemicals were (a) decreased production of indole-3-acetic acid and gibberellic acid and lower values of electrical conductivity, moisture content, weed density, and fresh and dry weight of weeds, and (b) increased production of abscisic acid and higher values of pH, Mn, Fe, Mg, Ca, K, 100-grain-weight, and fresh and dry weight of wheat plants.

Effects of milling time on hardness and electrical conductivity of in situ Cu–NbC composite produced by mechanical alloying

High-energy ball milling was used to synthesis in situ a copper-based composite. Cu, Nb and graphite powder mixture were mechanically alloyed in a planetary ball mill for various milling times (2, 8, 16 and 32 h), in an argon atmosphere. The nominal composition was Cu–11.77%Nb–1.52%C, which corresponded to Cu–15 vol.% NbC. XRD analysis showed that NbC particle was precipitated in the Cu–Nb–C after the sintering process. This particle had improved hardness of the in situ composite. This is attributed to the crystalline refinement and lattice strain of NbC due to the mechanical alloying. Low value of electrical conductivity was obtained in in situ composite as a result of electron scattering by fine NbC particle and copper grain. The results had shown that by increasing milling time both in situ and ex situ properties Cu–NbC composites were changed.