Saturated Electrical Conductivity Research Articles

Responses of the Soil Microbial Community to Salinity Stress in Maize Fields.

Simple SummarySoil microorganisms are the core of maintaining soil ecological functions. Recognition of microbial community diversity in saline soil contributes to nutrient management and crop production. Meanwhile, microbial activity is easily affected by changes in soil properties. This study addressed how the composition and diversity of bacterial and fungal communities changed under different saline conditions to identify the sensitivity of bacteria or fungi to salinity. The primary objective was to evaluate the relationship between soil’s microbial community diversity and soil’s physicochemical factors, and to explore the vital microbial predictors in salinized soil. The results showed that Firmicutes and Bacteroidetes are pivotal in salinized soil, and this finding can provide guidance for the demand for plant rhizosphere growth-promoting bacteria as a bioindicator in saline soil.To investigate the diversity and structure of soil bacterial and fungal communities in saline soils, soil samples with three increasing salinity levels (S1, S2 and S3) were collected from a maize field in Yanqi, Xinjiang Province, China. The results showed that the K+, Na+, Ca2+ and Mg2+ values in the bulk soil were higher than those in the rhizosphere soil, with significant differences in S2 and S3 (p < 0.05). The enzyme activities of alkaline phosphatase (ALP), invertase, urease and catalase (CAT) were lower in the bulk soil than those in the rhizosphere. Principal coordinate analysis (PCoA) demonstrated that the soil microbial community structure exhibited significant differences between different salinized soils (p < 0.001). Data implied that the fungi were more susceptible to salinity stress than the bacteria based on the Shannon and Chao1 indexes. Mantel tests identified Ca2+, available phosphorus (AP), saturated electrical conductivity (ECe) and available kalium (AK) as the dominant environmental factors correlated with bacterial community structures (p < 0.001); and AP, urease, Ca2+ and ECe as the dominant factors correlated with fungal community structures (p < 0.001). The relative abundances of Firmicutes and Bacteroidetes showed positive correlations with the salinity gradient. Our findings regarding the bacteria having positive correlations with the level of salinization might be a useful biological indicator of microorganisms in saline soils.

Reusing urine and coffee processing wastewater as a nutrient source: Effect on soil characteristics at optimum cabbage yield

Treatment and application of wastewater as a plant nutrient source is one of the waste management approaches currently used. This study attempted to investigate the effect of the application of human urine and coffee processing wastewater (UCPWW) on selected soil characteristics and compared it with rainwater and synthetic fertilizer in a completely randomized design. One-way analysis of variance (ANOVA) for difference and principal component analysis for correlation was employed. It was found that the soil organic carbon (SOC) and available phosphorus after production in a 1:2 ratio of UCPWW was significantly varied from the values before production and the soil treated with synthetic fertilizer (F=24.01, p=0.001; F=49.03, p=0.001, respectively). No significant difference was observed on micro-nutrients and the cation exchange capacity, but on some of the exchangeable cations: Na+(F=15.27, p=0.001) and Mg2+ (F=12.99, p=0.001) of 1:2 ratio application. The soil salinity was significantly increased and varied from other treatments: Na+ (F=11.88, p=0.04), Cl−(F=17.24, p=0.001), and total salinity (EC) (F=11.88, p=0.003), and significantly correlated with SOC and nutrients. The exchangeable sodium percentage (ESP), saturated electrical conductivity (ECe), and pH values for single round cultivation indicated no effects of sodicity, saline-sodicity, and salinity. However, the effect for repeated applications and cultivations, and mechanism of minimizing the salinity by the substrate should be studied before large-scale application.

Effects of wheat straw biochar and irrigation water on hydraulic and chemical properties of a sandy loam soil after faba bean cultivation

Nowadays, applying soil amendments is one of the most important ways to cope with water shortages and improve soil physical properties. In this regard, a greenhouse experiment was conducted to study the effect of different levels of irrigation water and wheat straw biochar on physical and chemical properties of a sandy loam soil, after harvesting faba bean. The experiment was performed with 5 biochar levels (0, 8, 16, 24 and 32 g kg-1) and 3 irrigation levels (100%, 75% and 50% of crop water requirement) using completely randomized design in three replications. Lowering the irrigation level to 50% did not influence soil physical and chemical properties except for saturated hydraulic conductivity (Ks), as Ks was significantly declined under 50% irrigation water levels as compared with full irrigation. Soil bulk density and particle density of 32 g kg-1 biochar treatment (B32) was reduced by 47% and 27%, respectively, while soil porosity and Ks increased as compared to no biochar application (B0). Under B32 treatment, the saturated electrical conductivity increased 5.6 times, and the cation exchange capacity and sodium adsorption ratio (SAR) was increased by 40.3% and 53.6% in comparison with B0, respectively. This made the soil saline (ECe>4 dS/m) but not sodic (SAR-1)1/2). It can be concluded that although, biochar level of 24 g kg-1 did not considerably increase soil water holding capacity compared to B0, it significantly improved the other soil physical and chemical properties, therefore, it can be used as soil amendment.

Mechanically Enhanced Electrical Conductivity of Polydimethylsiloxane-Based Composites by a Hot Embossing Process.

Electrically conductive polymer composites are in high demand for modern technologies, however, the intrinsic brittleness of conducting conjugated polymers and the moderate electrical conductivity of engineering polymer/carbon composites have highly constrained their applications. In this work, super high electrical conductive polymer composites were produced by a novel hot embossing design. The polydimethylsiloxane (PDMS) composites containing short carbon fiber (SCF) exhibited an electrical percolation threshold at 0.45 wt % and reached a saturated electrical conductivity of 49 S/m at 8 wt % of SCF. When reducing the sample thickness from 1.0 to 0.1 mm by the hot embossing process, a compression-induced percolation threshold occurred at 0.3 wt %, while the electrical conductivity was further enhanced to 378 S/m at 8 wt % SCF. Furthermore, the addition of a second nanofiller of 1 wt %, such as carbon nanotube or conducting carbon black, further increased the electrical conductivity of the PDMS/SCF (8 wt %) composites to 909 S/m and 657 S/m, respectively. The synergy of the densified conducting filler network by the mechanical compression and the hierarchical micro-/nano-scale filler approach has realized super high electrically conductive, yet mechanically flexible, polymer composites for modern flexible electronics applications.

Ionic and photosynthetic homeostasis in quinoa challenged by salinity and drought - mechanisms of tolerance.

Quinoa (Chenopodium quinoa Willd.) grown under field conditions was exposed to five irrigation water salinities (0, 10, 20, 30 and 40dSm-1; 4:1 NaCl:CaCl2 molar ratio) from flowering, and divided between full irrigation and progressive drought (PD) during seed filling. Quinoa demonstrated homeostatic mechanisms which contributed to quinoa's extraordinary tolerance. Salinity increased K+ and Na+ uptake by 60 and 100kgha-1, respectively, resulting in maintenance of cell turgor by osmotic adjustment, and a 50% increase of the leaf's fresh weight (FW):dry weight (DW) ratio and non-significant increase in elasticity enhanced crop water-capacitance. Day respiration (Rd) increased 2.7 times at high salinity but decreased 0.6 times during drought compared with control. Mesophyll conductance (gm) tended to be negatively affected by salinity as the increased succulence (FW:DW) possibly decreased intercellular space and increased cell-wall thickness. However, the increased K+ uptake seemed to alleviate biochemical limitations, as maximum Rubisco carboxylation rate (Vcmax) and photosynthetic electron transport (J) tended to increase under salinity. Overall, salinity and PD restricted stomatal conductance (gs) and photosynthesis (An) moderately, leading to decreased leaf internal to ambient [CO2], increase of intrinsic-water-use-efficiency (An/gs). The saturated electrical conductivity (ECe) resulting in 50% yield was estimated to be 25dSm-1, reaching no yield at 51.5dSm-1.

On the electrical conductivity of Ti-implanted alumina

Ion implantation of metal species into insulators provides a tool for the formation of thin, electrically conducting, surface layers with experimenter-controlled resistivity. High energy implantation of Pt and Ti into alumina accelerator components has been successfully employed to control high voltage surface breakdown in a number of cases. In the work described here we have carried out some basic investigations related to the origin of this phenomenon. By comparison of the results of alumina implanted with Ti at 75 keV with the results of prior investigations of polymers implanted with Pt at 49 eV and Au at 67 eV, we describe a physical model of the effect based on percolation theory and estimate the percolation parameters for the Ti-alumina composite. We estimate that the percolation dose threshold is about 4 × 1016 cm−2 and the maximum dose for which the system remains an insulator-conductor composite is about 10 × 1016 cm−2. The saturation electrical conductivity is estimated to be about 50 S/m. We conclude that the observed electrical conductivity properties of Ti-implanted alumina can be satisfactorily described by percolation theory.