Critical pH Value Research Articles

Integrating IoT for Soil Monitoring and Hybrid Machine Learning in Predicting Tomato Crop Disease in a Typical South India Station.

This study develops a hybrid machine learning (ML) algorithm integrated with IoT technology to improve the accuracy and efficiency of soil monitoring and tomato crop disease prediction in Anakapalle, a south Indian station. An IoT device collected one-minute and critical soil parameters-humidity, temperature, pH values, nitrogen (N), phosphorus (P), and potassium (K), during the vegetative growth stage, which are essential for assessing soil health and optimizing crop growth. Kendall's correlations were computed to rank these parameters for utilization in hybrid ML techniques. Various ML algorithms including K-nearest neighbors (KNN), support vector machines (SVM), decision tree (DT), random forest (RF), and logistic regression (LR) were evaluated. A novel hybrid algorithm, 'Bayesian optimization with KNN', was introduced to combine multiple ML techniques and enhance predictive performance. The hybrid algorithm demonstrated superior results with 95% accuracy, precision, and recall, and an F1 score of 94%, while individual ML algorithms achieved varying results: KNN (80% accuracy), SVM (82%), DT (77%), RF (80%), and LR (81%) with differing precision, recall, and F1 scores. This hybrid ML approach proved highly effective in predicting tomato crop diseases in natural environments, underscoring the synergistic benefits of IoT and advanced ML techniques in optimizing agricultural practices.

A salt/salt aqueous two-phase system based on pH-switchable deep eutectic solvent for the extraction and separation of mulberry polysaccharides

With the aim of expanding the potential application scope of mulberries, eleven pH-switchable deep eutectic solvents were screened for the ultrasonic-assisted extraction of mulberry polysaccharides, and a salt/salt aqueous two-phase system was constructed for the efficient separation of mulberry polysaccharides by regulating the system pH. DES-9 (tetraethylammonium chloride: octanoic acid molar ratio = 1: 2) with a critical response pH value of approximately 6.1 was concluded to be the best extraction solvent for extracting mulberry polysaccharides. A maximum polysaccharide extraction yield of 270.71 mg/g was obtained under the optimal conditions. The maximum polysaccharide extraction efficiency was 78.09 % for the pH-driven tetraethylammonium chloride/K2HPO4 aqueous two-phase system. An acidic β-pyran mulberry polysaccharide with a low-molecular weight of 9.26 kDa and a confirmed monosaccharide composition were obtained. This efficient and environmentally friendly polysaccharide separation method offers a new approach for the efficient extraction and utilization of other plant polysaccharides.

Enhancement of emulsion pH stability by Ca2+ modulation: A novel approach for preparing egg white protein fibril cold emulsion gels

Egg white, a crucial ingredient in bulk food production with limited emulsifying properties, can be significantly improved by fibrillation modification. However, resulting emulsions may exhibit instability at critical food processing pH values. In this study, the egg white protein fibril (EWPF) emulsion gel was constructed by Ca2+, and the stability enhancement mechanism under different EWPF and Ca2+ concentrations was investigated. The results showed that higher EWPF concentrations led to improved stabilization of the oil-water interface. At 60 mg/mL EWPF concentration, water loss decreased by 13.86% and oil loss by 35.79%, while the firmness and viscosity of the emulsion gel system were enhanced. The ζ-potential was reduced by 67.98% and the ionic bond content was increased by 22 times with the addition of Ca2+, the droplets showed a uniform cross-linked structure, and the stability and plasticity of the system were improved. By adjusting EWPF concentration to 40 mg/mL and Ca2+ concentration to 30 mM, pH stability of the system was also enhanced. This study provided a reference for the high-value utilization of egg white and a possibility for the application of EWPF in food processing, such as low-fat foods.

PH-Responsive Elastin-Like Polypeptide Designer Condensates.

Biomolecular condensates are macromolecular complexes formed by liquid-liquid phase separation. They regulate key biological functions by reversibly compartmentalizing molecules in cells, in a stimulus-dependent manner. Designing stimuli-responsive synthetic condensates is crucial for engineering compartmentalized synthetic cells that are able to mimic spatiotemporal control over the biochemical reactions. Here, we design and test a family of condensate-forming, pH-responsive elastin-like polypeptides (ELPs) that form condensates above critical pH values ranging between 4 and 7, for temperatures between 20 and at 37 °C. We show that the condensation occurs rapidly, in sharp pH intervals (ΔpH < 0.3). For eventual applications in engineering synthetic cell compartments, we demonstrate that multiple types of pH-responsive ELPs can form mixed condensates inside micron-sized vesicles. When genetically fused with enzymes, receptors, and signaling molecules, these pH-responsive ELPs could be potentially used as pH-switchable functional condensates for spatially controlling biochemistry in engineered synthetic cells.

Formation and microstructural characterization of scallop (Patinopecten yessoensis) male gonad hydrolysates/sodium alginate coacervations as a function of pH

Studying the noncovalent interactions between proteins and polysaccharides is quite important mainly due to the wide number of applications such as developing pH-responsive complexes. Scallop Patinopecten yessoensis male gonad hydrolysates‑sodium alginate (SMGHs-SA) was investigated as noncovalent complexes at pH from 1 to 10. The critical pH values pHC (around 6) and pHφ (around 4) were independent of the SMGHs-SA ratio, indicating the formation of soluble and insoluble complexes. The pH response of SMGHs-SA complexes was evaluated by investigating the rheological behavior, moisture distribution, functional group change and microstructure. Compared to the co-soluble and soluble complexes phases, the SMGHs-SA complexes had a higher storage modulus and viscosity as well as a lower relaxation time (T23) in the insoluble complexes phase (pHφ>3). Additionally, the amide I band and COO− stretching vibration peaks were redshifted and the amide A band vibration peaks were blueshifted by acidification. Electrostatic interactions and intermolecular/intramolecular hydrogen bonding led to SMGHs-SA agglomeration at pH 3, forming a uniform and dense gel network structure with strong gel strength and water-retention capacity. This study provides a theoretical and methodological basis for the design of novel pH-responsive complexes by studying SMGHs-SA complex coacervation.

Improving physical stability of pea protein-based emulsions near the isoelectric point via polysaccharide complexation

Development of plant protein-based mildly acidic beverages remains challenging as the pH range falls near the protein isoelectric point, destabilizing emulsions. To overcome this problem, it was hypothesized that complexation between plant proteins and polysaccharides could provide emulsion stability in this critical pH range. Four different polysaccharides (sugar beet pectin, gum Arabic (GA), guar gum, gellan gum) were mixed separately with pea protein isolate (PPI) in 1:1 ratio, and the critical pH values for the formation of soluble complexes were determined. Heating the mixture widened the optimal pH range for soluble complexation for pectin-PPI and GA-PPI below the isoelectric point, which was then used to prepare 5 wt% O/W emulsions with an aqueous phase containing 0.5 wt% biopolymers at pH 8.0 and pH 4.5. Emulsion stability was characterized using droplet size, charge, visual observation, microstructure, and accelerated gravitational separation. PPI-only emulsions were stable at pH 8.0 but extensively destabilized at pH 4.5. The GA-PPI emulsions showed high stability at pH 8.0; however, at pH 4.5, the soluble complexes failed to provide a stable emulsion due to extensive droplet aggregation and phase separation. The emulsion prepared with a co-soluble pectin-PPI mixture at pH 8.0 also showed droplet aggregation and phase separation. The most improved emulsion stability (smallest droplet size, no aggregation) was observed for the pectin-PPI soluble complex at pH 4.5. Findings from this study showed that soluble complexes could be obtained at the desired pH range depending on the polysaccharide sources, which can stabilize O/W emulsions even near the protein's isoelectric point.

Phase behavior and complex coacervation of whey protein isolate-Tremella fuciformis polysaccharide solution

Different methods were used to monitor transformations and protein-polysaccharide complexes formation resulting from the interaction of whey protein isolate (WPI) and Tremella fuciformis polysaccharide (TPS) over the pH range of 2.0–7.0. WPI:TPS in the range of ratios from 16:1 to 2:1 were used along with the biopolymer concentrations of 0.1%–1% by mass. The binding properties of WPI to TPS and thermodynamic parameters for this interaction were analysed and calculated. WPI:TPS complex coacervates properties including viscoelasticity, secondary structure, and microstructure were studied. Results showed that both the WPI:TPS ratio and biopolymer concentration altered phase boundaries and critical pH values. For the 0.1% solution, the optimum for WPI:TPS coacervate formation occurred at pH 3.2 and WPI:TPS ratio of 2:1. When the maximum coacervate precipitation formed, the solution presented the least pronounced shear-thinning behavior and the lowest apparent viscosity value. By WPI:TPS interaction, the secondary structure of WPI was altered. Compared to gum Arabic (GA), TPS showed a stronger affinity towards WPI with higher binding sites (1.93–3.65) and binding constant 1.95 × 1010–5.25 × 1019 over temperatures from 288 K (14.85 °C) to 310 K (36.85 °C). Negative values of Gibbs free energy of WPI:TPS (−65.12 to −122.66 kJ/mol) and WPI:GA (−14.38 to −10.18 kJ/mol) combinations suggested binding occurred spontaneously. The WPI:TPS coacervates formed were given a stronger gel-like structure and higher density than the WPI:GA coacervate. Thus, the WPI:TPS coacervates have more potential to be the new alternatives for nutrient microencapsulation.

Destabilization of oil-in-water emulsions: Influences of interfacial assembly of octenyl succinic anhydride starch and chitosan

This study investigated the formation and destabilization of emulsions with different interfacial assemblies of octenyl succinic anhydride starch (OSAS) and chitosan (CS) at critical pH values. All emulsion droplets were connected to each other via bridging of interfacial percolation and observed to form gel network structures during prolonged storage. In addition, partial pH-dependent flocculation occurred during preparation and decreased the degree of coalescence and creaming of emulsions. Compared to bilayer (OSAS-CS and CS-OSAS) emulsions, the complex (OSAS/CS)-stabilized emulsions were more resistant to coalescence, creaming, and lipid oxidation because of their thick interfacial layers (∼2 μm) and tight percolation networks. The layer-by-layer adsorption of OSAS and CS at the interface may lead to reduced homogeneity and stability of the bilayers, making them relatively susceptible to destabilization. Moreover, an appropriate pH (6.0) facilitated the oxidation stability of emulsions by influencing inter-droplet electrostatic interactions. For complex-stabilized emulsions, the lipid hydroperoxide content at pH 6.0 was reduced by approximately 22.85% and 12.26% respectively compared with that at pH 5.5 and pH 6.5. This work may provide promising insights into the rational design of emulsions with desirable stability by combing biopolymers.

Agaricus bisporus Wild Mushroom Extract as Lectin Source for Engineering a Lactose Photoelectrochemical Biosensor

Agaricus bisporus mushroom biomass contains a lectin, ABL, with remarkable specificity for lactose biorecognition; in this work, this feature was explored to develop a photoelectrochemical biosensor. The high lectin activity found in saline extracts of this macrofungus (640 HU mL-1), even at critical pH values (4-10) and temperatures (20-100 °C), allowed its direct use as an ABL source. Theoretical and experimental evidence revealed favorable electrostatic and biocompatible conditions to immobilize ABL on a poly(methylene blue)/fluorine-doped tin oxide-coated glass platform, giving rise to the ABL/PMB/FTO biosensor. The conducting polymer added further photoactivity to the device, allowing the identification of lectin-carbohydrate interactions with even greater sensitivity. The dose-response curves studied by electrochemical impedance spectroscopy showed a sigmoidal profile that was well-fitted by Hill's equation, expanding the working dynamic range (15-540 nmol L-1 lactose; 20.2 pmol L-1 detection limit) and avoiding undesirable sample dilution or preconcentration procedures. Under the optimized photoelectrochemical conditions, the ABL/PMB/FTO biosensor showed remarkable signal stability, accuracy, specificity, and selectivity to analyze lactose in commercial food products. This research raises interest in ABL-based biosensors and the added value of the crude Agaricus bisporus extract toward the development of greener and more sustainable biotechnological approaches.

Rheological characterization of low methoxyl pectin extracted from durian rind

Pectin's rheological properties are closely related to its functionality for food and pharmaceutical applications. In this study, the flow behavior and viscoelastic properties of durian rind pectin (DP) (esterification degree = 18.99%, molecular weight = 42.1 kDa) were evaluated at different concentrations (1.0–3.0% w/v), pH (2.0–6.0), and temperatures (flow behavior: 10–75 °C, viscoelastic properties: 5–90 °C). DP solutions had pseudoplastic behavior. The viscosities of DP solutions improved at rising concentrations and decreasing pH, whereas their viscosities dropped at increasing temperatures. The viscosities of commercial low methoxyl pectin (CLMP) solutions were greater than DP under the same conditions due to their greater molecular weight. DP gels, at a constant level of 50 mg Ca2+/g pectin and 30% sucrose (w/v), had greater gel strength at increasing pectin concentration and at a critical pH value (pH 3.0). The strongest gel was obtained at 3.0% (w/v) pectin concentration and pH 3.0, exhibiting greater gel strength than CLMP under the same condition. DP and CLMP gels remained gel-like throughout continuous heating and cooling, showing good thermal stability. Therefore, DP is a potential gelling and thickening agent for weak-acid-low-calorie food and pharmaceutical applications under a broad temperature range.

Transition of self-passivation and semiconductor property of titanium in the simulated environments of proton exchange membrane fuel cells

In this work, the passivation behaviors of titanium at various solution acidities are investigated in the simulated environments of proton exchange membrane fuel cells. The results show that there is a critical pH value to initiate the self-passivation of titanium, and a mathematic method based on the potentiodynamic polarization curve analysis is proposed to verify this value. The semiconductor type of the passive film changes from n-type to bipolar type, then to p-type as the pH increases, which can be explained by an n/p junction model. In addition, the relationship of the passive film thickness and pH is consistent with the prediction of point defect model.

Influence of fulvic acid sub-fractions on aggregation kinetics of graphene oxide in aqueous environments

Fulvic acid (FA) can affect the dispersion of graphene oxide (GO) in aquatic environments, however, the possible mechanisms remain unclear. Dynamic light scattering techniques combined with a multiple regression model were applied to explore the influence of FA sub-fractions (FApH3 − FApH13) on the aggregation kinetics of GO in aqueous environments. The ratios of critical coagulation concentration (CCC) values were CCCNa: CCCMg: CCCLa: CCCCe = 1:2–5.15:3–7.31:3–7.35, which were consistent with the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory and Schulze−Hardy rules. The GO remained stable at pH 3–10 and aggregated at pH < 3 or pH > 10, and its critical coagulation pH values were 1.44 and 12.25 with 10 mM NaCl as background. The CCC values of GO in the presence of FApH3 − FApH13 were greater than those in the absence of FA sub-fractions. The ratios of CCC values of GO (r) increased in the presence of FA sub-fractions in the order of FApH13 > FApH9 > FApH7 > FApH5 > FApH3 and ranged from 1.01 to 2.15 for certain metal ions including Na+, Mg2+, La3+, and Ce3+. The CCC values of GO were significantly related to C, H, O, N, S, H/C, O/C, carboxylic C, and carbonyl C of FA sub-fractions (P < 0.05), respectively, and could be predicted using the multiple linear regression eq. CCC = Z-n (98.959– 60.911 ∗ O/C + 4.799 ∗ O-alkyl C – 0.845 ∗ aromatic C – 6.237 ∗ carbonyl C). The predicted CCC values for GO were within 90 % prediction intervals, and the average error of the CCC values was 3.3 % and R2 = 0.986. This investigation is expected to provide a scientific basis for the transport and ecotoxicity of GO in environments.

Complex coacervation of α-lactalbumin with gum arabic: Effect of environmental condition, mass ratio, and biopolymer concentration

The coacervate formation and interaction between α-lactalbumin (ALA) and gum arabic (GA) was investigated with turbidimetric analysis, fluorescence spectroscopy, atom force microscopy (AFM), and isothermal titration calorimetry (ITC). Critical pH values (pH c , pH φ1 , pH opt and pH φ2 ) of phase transitions for ALA-GA complexes (1:1, 0.1%, w/v) without NaCl, representing the formation of soluble and insoluble complexes, were 4.95, 3.85, 3.70, and 2.30, respectively. pH and NaCl concentrations are dominant in influencing the formation of ALA-GA complexes. AFM graphs evidently indicated the formation, association, and dissociation of ALA-GA complex. ITC results confirmed that the formation of soluble ALA/GA complex was a spontaneous exothermic process, and the electrostatic interaction between ALA and GA was stronger at pH 3.0 than that at pH 4.9 and 5.6. The obtained information of this study provides insights into the interaction between ALA and GA and expands the application of ALA-based formulations in food systems with desirable functionality. • pH and NaCl concentrations are dominant in affecting the complexation of ALA-GA. • The mechanisms underlying ALA-GA complexation become more explicit; • AFM graphs showed the formation, association, and dissociation of ALA-GA complex; • ITC proved the formation of soluble ALA-GA complex was spontaneously exothermic.

Effect of ionic strength and mixing ratio on complex coacervation of soy protein isolate/Flammulina velutipes polysaccharide

Soy protein isolate (SPI) is a commercial protein with balanced amino acids, while the poor solubility impedes its use in traditional foods. To overcome the problem, the complex coacervation of SPI/Flammulina velutipes polysaccharide (FVP) were investigated. Initial results revealed that the suitable amounts of FVP contributed to reducing the turbidity of SPI solution. Under electrostatic interaction, the formation of SPI/FVP coacervates were spontaneous and went through a nucleation and growth process. Low salt concentration (CNaCl = 10, 50 mmol/L) led to an increase in the critical pH values (pHc, pHφ1) while the critical pH values decreased when CNaCl ≥ 100 mmol/L. The concentration of NaCl ions increased the content of α-helix. With the increase of FVP, the critical pH values decreased and the content of β-sheet increased through electrostatic interaction. At SPI/FVP ratio of 10:1 and 15:1, the complex coacervation of SPI/FVP were saturated, and the coacervates had the same storage modulus value. SPI/FVP coacervates exhibited solid-like properties and presented the strongest storage modulus at CNaCl = 50 mmol/L. The optimal pH, SPI/FVP ratio and NaCl concentration of complex coacervation were collected, and the coacervates demonstrated a valuable application potential to protect and deliver bioactives and food ingredients.

Zinc sulfide-chitosan hybrid nanoparticles as a robust surface for immobilization of Sillago sihama α-amylase

In the present study, zinc sulfide-chitosan hybrid nanoparticles synthesized by chemical deposition were used as a matrix for the immobilization of purified α-amylase extracted from Sillago sihama (Forsskal, 1775). In this regard, the size and morphological structure of zinc sulfide-chitosan hybrid nanoparticles before and after the stabilization process were evaluated using FT-IR, DLS methods, as well as SEM and TEM electron microscopy, and EDS analyses. Then, the efficiency of the immobilized enzyme was measured in terms of temperature, optimal pH, stability at the critical temperature, and pH values. Immobilization of α-amylase on zinc sulfide -chitosan hybrid nanoparticles increased the long-term stability, as well as its endurance to critical temperatures and pH values; however, the optimal temperature and pH values of the enzyme were not altered following the immobilization process. The kinetic parameters of the enzyme were also changed during immobilization. Enzyme immobilization increased the Km, whereas decreased the catalytic efficiency (Kcat / Km) of the immobilized enzyme compared with the free enzyme. These results are very important as, in most cases, enzyme immobilization reduces the activity and catalytic efficiency of enzymes. The nano-enzyme produced in this study, due to its high temperature, and pH stability, could be a good candidate for industrial applications, especially in the food industry.

Elucidation of critical pH-dependent structural changes in Botulinum Neurotoxin E

Botulinum Neurotoxins (BoNT) are the most potent toxins currently known. However, they also have therapeutic applications for an increasing number of motor related conditions due to their specificity, and low diffusion into the system. Although the start- and end- points for the BoNT mechanism of action are well-studied, a critical step remains poorly understood. It is theorised that BoNTs undergo a pH-triggered conformational shift, activating the neurotoxin by priming it to form a transmembrane (TM) channel. To test this hypothesis, we combined molecular dynamics (MD) simulations and small-angle x-ray scattering (SAXS), revealing a new conformation of serotype E (BoNT/E). This conformation was exclusively observed in simulations below pH 5.5, as determined by principal component analysis (PCA), and its theoretical SAXS profile matched an experimental SAXS profile obtained at pH 4. Additionally, a localised secondary structural change was observed in MD simulations below pH 5.5, in a region previously identified as instrumental for membrane insertion for serotype A (BoNT/A). These changes were found at a critical pH value for BoNTs in vivo, and may be relevant for their therapeutic use.

Formation and stability of electrostatic complexes formed between scallop female gonad protein isolates and sodium alginate: Influence of pH, total concentration, blend ratio, and ionic strength.

The complex coacervation between scallop (Patinopecten yessoensis) female gonad protein isolates (SFGPIs) and sodium alginate (SA) was determined by the turbidimetric method. The impact of pH, total biopolymer concentration, biopolymer blend ratio, and various salt ionic on the mechanisms governing the complex coacervation of SFGPIs-SA complexes were also investigated. For the SFGPIs:SA ratio of 2:1 without adding NaCl, insoluble and soluble complexes were observed at pH 5.8 (pHφ1 ) and pH 8.2 (pHc ) with the optimum biopolymer interactions appearing at pH 2.6 (pHopt ). The maximum turbidity value increased with the increment of the total biopolymer concentration from 0.37 to 1.83 until attaining the critical value (0.75%). As the blend ratios rose from 1:3 to 12:1, the critical pH values (pHc , pHφ1 , and pHopt ) moved to higher pH. Furthermore, the addition of NaCl led to a remarkable decrease in turbidity over the whole pH region in SFGPIs-SA complexes. Moreover, monovalent ions (Na+ and K+ ) had the same effect on the formation of the SFGPIs-SA complex, whereas the divalent cations (Mg2+ and Ca2+ ) lessened the complex formation in comparison with the monovalent ions. This study offers a methodological and theoretical basis for the design of complex SFGPIs-SA systems by understanding the complex coacervation under different conditions. PRACTICAL APPLICATION: In recent years, several protein-polysaccharides complexes have been widely applied in food and biological systems. Scallop (Patinopecten yessoensis) female gonads are deemed as good marine sources for developing protein matrices on account of their high protein content and nutrients. In our study, the effects of different conditions on the mechanisms governing the complex coacervation of SFGPI-SA mixtures were investigated, and the instability of the system could be overcome by understanding the conditions for SFGPIs/SA complex formation, which have a feasible role in developing marine source-protein as afunctional food base such as kamaboko gels, can, sausage, fat substitutes, and delivery vehicles for bioactive compounds.

Comparative analysis of two hydrogel architectures synthesized by gamma radiation based on dimethylacrylamide and acrylic acid grafted on polyethylene

This study reports the synthesis of new modified polymeric systems that could be applied to the upload and delivery of drugs using gamma radiation. It is known that different architectures with the same components results in different properties, and it is therefore of interest to compare them. Two different systems were prepared using a polyethylene (PE) matrix grafted with a comb-type hydrogel based on N, N-dimethylacrylamide (DMAAm) and acrylic acid (AAc) and one interpenetrating network of the same monomers. First, PE was grafted onto DMAAm using gamma radiation under different reaction conditions, which involved changes in the absorbed dose, solvents, and concentration. Second, a crosslinked hydrogel network of DMAAm grafted onto a PE film surface was obtained by gamma radiation and subsequently modified with AAc to form two different architectures: a comb-type graft [PE-g-(net-DMAAm)]-comb-AAc and an interpenetrating network grafted onto PE, PE-g-[(net-DMAAm)-inter-(net-AAc)]. To evaluate the effect of the grafting reaction on the hydrophilicity, swelling studies were performed and the critical pH values were determined. The obtained systems were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), mechanical properties, and Scanning Electron Microscopy (SEM). Comparison between the properties of both systems was done.

Evaluation of Mehlich‐3 for determination of cation exchange capacity in Kansas soils

AbstractSoil testing laboratories across the United States have implemented the Mehlich‐3 (M3) extraction method for phosphorus (P) and other nutrients. Though M3 is known to work well as a multinutrient extractant, it raises concerns for measuring exchangeable cations, particularly in calcareous soils. The objectives of this study were (a) to evaluate M3 as an extractant for base cations for Kansas soils, (b) to identify a range of soil pH where M3 may be a suitable replacement for ammonium acetate (AA), and (c) to examine the relationship between cation exchange capacity (CEC) summation and CEC displacement. A study was conducted evaluating 308 soils collected from across Kansas and extracted using both the M3 and AA soil extraction methods. Cation exchange capacity was estimated using the summation approach from measurements of both the M3 and AA, and the displacement method. Results indicate a strong correlation among M3 and AA methods for K, Mg, and Na (R2 = .98, .96, .97, respectively). However, these relationships were considerably weaker for extractable Ca (R2 = .78), where extractable Ca was higher in the M3 extracts for high pH soils. Estimated CEC was also affected by soil pH for the M3 method, with an estimated critical pH value of 7.3. Extractable Ca and CEC for soils with a pH below 7.3 showed a strong correlation between M3 and AA methods (R2 = .9). Using M3 as a multinutrient extractant can improve turnaround time for sample analysis in soil testing laboratories. However, the use of the M3 procedure in soils with a pH of 7.3 or above will likely result in overestimation of exchangeable Ca and CEC.

Mitigating cadmium contamination of rice soils supporting tobacco–rice rotation in southern China: Win–win or lose–lose?

The present study evaluates the sustainability of tobacco-rice rotation by reducing the phytoavailability of cadmium (Cd) to rice by combining large-scale field sampling and regional investigations in southern China. The rotation involves frequent tillage and liberal application of nitrogen and phosphorus fertilizers, which increases yields but lowers soil pH. As a result, manganese is lost from soil and, at the same time, more soil Cd is taken up by rice and tobacco. The tendency to overcompensate for the Mn loss is influenced by soil properties, crop type, and economics of cultivation. Based on the scenario analysis, this tendency and the Cd uptake risks were estimated. Dietary intake of 83.3% of rice grain produced on the rotation fields would have adverse health effects on local male nonsmokers. Besides the rice, Cd in local tobacco leaf may lead to an increase in the kidney Cd levels of local male smokers (21.5 cigarettes per day) by 16.2-fold at age 50. Field trials and model estimations indicated that for a Cd concentration below 0.2 mg dry weight kg-1 in rice grain, the critical pH value in rice soils was ~ 6.0, and that for amorphous Mn oxide at pH 4.5–6.0 was 120 mg kg−1.