Immobile Water Content Research Articles

Investigation of short‐term effects of forage radish on water and solute transport through a tracer test and inverse modeling

AbstractThe benefits of using cover crops for improving soil and water quality are well known. Less clear is whether cover crops, especially those forming a taproot system, can favor solute transport down to the groundwater by modifying soil hydraulic properties and solute dynamics. In this study, we employed 12 lysimeters to conduct a comparative analysis between a taproot cover crop, specifically forage radish (FR), and bare soil (BS), under three water table management conditions. Our objective was to evaluate whether the enhancement of root‐derived macroporosity could have modified water and solute dynamics, and offset the benefits provided by FR that is commonly used to mitigate solute leaching. A tracer solution of bromide (Br−) was added to lysimeters, and solute flux concentrations were determined at different depths during a 25‐day test. Soil moisture and pressure heads were monitored. Water and solute transport parameters were estimated by inverse modeling using HYDRUS‐1D. A complementary laboratory experiment was performed to quantify the effect of FR root apparatus on the macropore structure by using noninvasive X‐ray microtomography (µCT). Results showed that the growth of FR within the lysimeters induced alterations in water and solute dynamics compared with BS. This is primarily attributed to its proficiency as solute scavenger, with an uptake capacity of up to 47% of the total injected tracer. Our comparative analysis instead revealed subtle differences in soil structure and hydraulic properties brought about by the presence of FR. Major changes were observed for the saturated hydraulic conductivity (Ks), which increased from an average of 8.4–49.8 cm day−1 within the 20–45 cm layer in BS and FR, respectively. Additionally, there was a difference in immobile water content (θim), with the values in FR averaging 21% lower than those in BS. These modifications can be attributed to the formation of fissures and channels, primarily concentrated in the proximity of taproot development, without extending into deep preferential flow pathways. These structural changes were supported by the nondestructive µCT analyses. Upon aggregating the effects observed, solute movement to groundwater was not affected by FR compared to BS conditions.

Use of basic amino acids to improve gel properties of PSE-like chicken meat proteins isolated via ultrasound-assisted alkaline extraction.

To improve the gel quality of pale, soft, and exudative (PSE)-like chicken protein isolate (PPI) obtained via ultrasound-assisted alkaline extraction (UAE), l-lysine (l-Lys), l-arginine (l-Arg), or l-histidine (l-His) were used and the effects on the thermal gelling characteristics of PPI were studied. Compared with the nonbasic amino acid addition group, the addition of l-His/l-Arg/l-Lys significantly increased the solubility and absolute zeta potential of PPI, whereas reduced the particle size and turbidity (p<0.05). They enhanced the gel strength and textural properties of PPI (p<0.05) and reduced the cooking loss of PPI in the following order: l-Lys>l-Arg>l-His. The solubility, gel strength, and hardness of PPI with l-Lys were increased by 18.6%, 44.6%, and 57.6%, respectively, and cooking loss was decreased by 18.1%. Low-field nuclear magnetic resonance and magnetic resonance imaging revealed that basic amino acids addition decreased the water mobility in PPI gels with increasing immobile water content. Scanning electron microscopy revealed that the addition of basic amino acids promoted the formation of a more uniform and tight network microstructure in PPI gels. The α-helix content was decreased, whereas the β-sheet content was increased in PPI gels after basic amino acid addition. Therefore, addition of basic amino acids, especially l-Lys, enhances the gel properties of PPI. PRACTICAL APPLICATION: This study revealed that adding basic amino acids effectively improved the gel properties of PPI obtained via UAE method, with l-Lys exerting the best improvement effect. Our findings highlight the application value of PSE-like meat by the improvement of gel characteristics of PPI, providing a theoretical reference for the processing and utilization of PPI.

Exploring the interaction between Lycium barbarum polysaccharide and gelatin: Insights into gelation behaviors, water mobility, and structural changes

Gelatin-polysaccharide interactions have garnered significant attention in recent years due to their profound effects on the properties (rheology and structure) of various food products. This study investigates the interaction between Lycium barbarum polysaccharide (LBP) and gelatin, focusing on the impact of different concentrations LBP (0–2.0%, w/v) on gelation behavior, water mobility, and gelatin structure. The results show that the addition of LBP initially increases and then decreases the gel strength and hardness of the gelatin. Incorporating LBP into gelatin leads to decreased brightness, gelling temperature (Tg), gelation rate (kgel), immobile water content, and residue, while increasing the redness, yellowness, bound and free water content, and thermal stability. Fourier transform infrared spectroscopy (FTIR), x-ray diffractometer (XRD), cryogenic scanning electron microscopy (Cryo-SEM), and atomic force microscopy (AFM) analyses provide evidence for the existence of hydrogen bonds, electrostatic interactions, and ionic bond interactions between LBP and gelatin, in addition to covalent bonds formed through the Maillard reaction. Moreover, LBP induces changes in the structure of gelatin, including alterations in secondary structure, crystalline structure, and microstructure. AFM observations further indicate that LBP promotes the formation of gelatin aggregates. These findings present promising avenues for the application of LBP-gelatin composite gels as novel materials in the food industries.

Effect of citrus fiber on the phosphate-mediated gel properties of myofibrillar protein and partial replacement of phosphate

To evaluate the effect of citrus fiber (CF) on the phosphate-mediated gel properties of myofibrillar protein (MP) and partial replacement of phosphate, gels properties, emulsifying properties, molecular forces and structural characteristics, water distributions, microstructure of MP composite gels with sodium tripolyphosphate (STP) and CF were investigated. The results showed that the addition of STP and CF could enhance the gel properties by unfolding the structure of α-helix, and increasing the hydrophobic interactions and hydrogen bonds, which were the primary molecular forces to stabilize the structure of MP-STP-CF composite gels. The measurement of relaxation time and microstructure further verified that STP and CF could convert more free water into immobile water, forming a more stable three-dimensional network structure. MP gel added with 5% STP and 10% CF exhibited the best gel properties, but excessive CF addition would weaken the intermolecular forces and immobile water content, then destroyed the gel properties. Moreover, MP gel with 3% STP and 10% CF addition had no significant difference on the gel properties and structures compared with MP gel with 5% STP. The results provided basic theoretical support for the application of CF in improving the structure of meat products and the partial substitution of phosphate.

Effect of heat‐treatment times on the microstructure and water absorption properties of sea cucumber

SummaryIn order to explore the relationship between water absorption properties and microstructure changes of sea cucumber body wall with different heat treatments. The microstructure, rheological characteristics and hydrogen bond content changes of sea cucumber body wall at different heat‐treatment times (4, 6, 8, 10 and 12 h) were investigated, as well as the distribution and phase of water during the soaking. The results showed that the heat treatment for 4 and 6 h mainly caused fibre fracture which led to more water binding sites and free water content. With prolonged heat‐treatment times, the degree of denaturation increases. The micro‐pores formed at 10 h heat treatment could accommodate the highest free water content, and the network structure was more intensive at 12 h with decreased porosity. The apparent viscosity, storage and loss modulus gradually decreased with heat‐treatment time, and the liquidity increased. Extended heat‐treatment time led to the breakage of the microstructure, and the longer time required for its free water and immobile water content to reach the maximum. However, the trend of bound water was the opposite.

Effects of active modified atmosphere on lipid and protein oxidation, moisture migration and quality properties of beef steaks

Fresh beef is a typically perishable food because of its high water and protein content; thus, it requires proper packaging condition and storage temperature to ensure its quality. In this study, the beef steaks were stored at 4°C under HiO2 modified atmosphere packaging (MAP) (78.8% O2 + 18.8% CO2 + 2.4% N2) and HiCO2 MAP (60.0% CO2 + 40.0% N2). The traditional air packaging (AP) and vacuum packaging (VP) were used as the controls. The total viable count (TVC), colour, water holding capacity (WHC), myofibrillar protein (MP) oxidation and lipid oxidation of beef meat were investigated. The moisture distribution and migration were also analysed using the low‐field nuclear magnetic resonance (LF‐NMR). The association amongst all parameters was analysed by correlation analysis and principal component analysis (PCA). The results showed that the TVC values in the HiCO2 MAP (5.6 log CFU/g) steaks were lower than those of VP (5.9 log CFU/g), AP (7.0 log CFU/g) and HiO2 MAP (6.3 log CFU/g) steaks because of the sufficient CO2 after 15 days of chilled storage. The bright red colour and the higher WHC were maintained in the HiO2 MAP steaks than in the AP group during storage. However, higher levels of protein and lipid oxidation also occurred. The beef steaks stored under HiCO2 MAP had the lowest protein and lipid oxidation and highest value of immobile water content and WHC, however, similar to the VP group, the bright red colour was not shown. The moisture attributes (drip loss, cooking loss and P23), protein oxidation (protein solubility and carbonyl content) and lipid oxidation (TBARS value) have shown a close correlation by correlation analysis and PCA. Overall, two different packaging methods of MAP can prolong microbial‐shelf life and maintain higher WHC of beef steaks compared to AP and VP steaks, but higher oxidation level in HiO2 MAP and unattractive colour in HiCO2 MAP are concerns that need to be addressed.

Effects of High-Voltage Atmospheric Cold Plasma Treatment on Microbiological and Quality Characters of Tilapia Fillets.

Cold plasma (CP) has become an alternative to conventional thermal processing of food products. In this study, the effect of cold plasma treatment time on the inactivation and quality of tilapia fillets was investigated. The surfaces of tilapia fillets were inoculated with Salmonella enteritis (S. enteritis), Listeria monocytogenes (L. monocytogenes), and a mixture of both before being treated with cold plasma at 70 kV for 0, 60, 120, 180, 240, and 300 s. With the extension of treatment time, the number of colonies on the surface of the fillets decreased gradually; after 300 s of cold plasma treatment, S. enteritis and L. monocytogenes populations were reduced by 2.34 log CFU/g and 1.69 log CFU/g, respectively, and the a* value and immobile water content decreased significantly (p < 0.05), while the free water content increased significantly (p < 0.05). TBARS value increased significantly (p < 0.05) to 1.83 mg MDA/kg for 300 s treatment. The carbonyl value and sulfhydryl value of sarcoplasmic protein significantly (p < 0.05) increased and decreased, respectively, as treatment time extension, while no significant changes were found in myofibrillar protein. No significant differences were observed in pH, b* value, elasticity, chewiness, thiol value, and TVB-N value. The results showed that cold plasma had an inactivation effect on tilapia fillets and could preserve their original safety indicators. It was concluded that CP treatment could be used as an effective non-thermal method to maintain the quality of tilapia fillets and extend their shelf-life.

Study on the immobile water of saturated compacted clay-rich materials by oil seepage

Immobile water is defined as a firmly bound thin film of water surrounding clay particles that somehow resembles solid features. The characteristics and amount of immobile water depend on pore water chemistry, the type of clay, and the contact area of water with particles. Seepage can occur only when the hydraulic gradient increases sufficiently. To date, no accurate method is available to determine the immobile water content. Therefore, an approach is proposed for direct measurement of the immobile water content, which applies vegetable oil to displace water in saturated compacted clay-rich materials. Under a high hydraulic gradient, the vegetable oil completely displaces the free porewater in the clay-rich materials, and the remaining residual water is assumed to be immobile water. By using carbon tetrachloride (CCl4) as an extracting agent, the oil in the permeated sample was subjected to extraction and distillation, and the total liquid content was determined by the oven-drying method. As a final step, the immobile water content in the sample was calculated. A high-speed centrifugation method was used to determine the immobile water content from the corresponding soil water potential, which accounted for approximately 634.3 kPa. It was found that the immobile water of the clay-rich materials was essentially equal to the bound water. The effective porosity of clay was obtained based on the immobile water content. By comparing the relationship between porosity, effective porosity and hydraulic conductivity, the effective porosity revealed an improved linear relationship with log (k). The test results show the oil seepage method to be useful and reliable for the quantification of the immobile water content of saturated compacted clay-rich materials.

Effects of different metal ions on the physicochemical properties and microstructure of egg white gel.

To ameliorate egg white gel's salinity and undesirable texture characteristics during curing, different metal ions (K+ , Mg2+ , Ca2+ , Zn2+ ) were used to replace sodium chloride (NaCl) to simulate salted eggs partially. The effects of these ions on the physicochemical properties, microstructure, and gel characteristics of egg white protein were studied. Low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) analysis showed that adding K+ , Mg2+ , Ca2+ , and Zn2+ could decrease immobile water content and increase free water content in egg white gel. Circular dichroism/fluorescence spectrophotometry (CD/FL) analysis showed that substitutive addition of K+ , Mg2+ , Ca2+, and Zn2+ changed the conformational structure of the protein, which was not conducive to the formation of the three-dimensional mesh gel structure. Differential scanning calorimetry (DSC) results show that the addition of four metal ions could reduce the thermal denaturation temperature of egg white gel. Scanning electron microscopy (SEM) showed that the gel structure of egg white in the zinc chloride (ZnCl2 ) group was rougher and more chaotic, the crosslinking degree was worse, so it was not suitable for low sodium salted egg preparations. The gel strength of the calcium chloride (CaCl2 ) group was significantly higher than other groups (P < 0.05), while the gel strength of the potassium chloride (KCl) group was similar to the NaCl group (P > 0.05). CaCl2 and KCl could be used as partial NaCl substitutes to study the addition level and ratio further and improve salted egg white quality. © 2021 Society of Chemical Industry.

Effects of NaCl and soy protein isolate on the physicochemical, water distribution, and mobility in frankfurters

SummaryIn this study, we investigated the effect of gel and rheological properties, microstructure, and water distribution of frankfurters with various amounts of NaCl (1 and 2%) and soy protein isolate (SPI, 3 and 6%). The frankfurter cooking yield, a*value, and hardness significantly increased with the increasing NaCl and SPI content. However, the frankfurter springiness and cohesiveness were lower in the case of 6% SPI and 2% NaCl content than in the case of 3% SPI and 2% NaCl content. The thermal stability of myosin improved with the increasing NaCl and SPI, resulting in more compact and continuous structures. Meanwhile, the initial T2b, T21, and T22 relaxation times were significantly shorter, and the P21 and P22 peak ratios increased and decreased significantly, respectively, implying the increase of the immobile water content. Overall, the SPI use allowed the production of reduced‐salt frankfurter with desirable quality.

Long-term effect of magnesium and iron nanoparticles on solute transport in saturated condition

ABSTRACT The aim of this study was to investigate the long-term effect of magnesium and iron nanoparticles on solute transport and its parameters, which has not been investigated to date. Different concentrations of two types of nanoparticle metal oxides, MgO and Fe3O4, were mixed with a loamy soil and their effects on solute transport and its parameters after three years were investigated. Nanoparticles improved soil structure through increased macro pores compared to the control, by 2.3% in the 3% concentration of MgO to 15.3% in the 3% concentration of Fe3O4. Immobile water content of the soil decreased from 0.42 in the control to 0.05–0.24 cm3 cm−3 in the treatments. The mass transfer coefficient was decreased from 0.48 in the control to 0.005–0.37 in the nanoparticle treatments. Moreover, nanoparticles increased the breakthrough curve peak concentration and decreased discharge time of chloride in the extract from 0.41 and 88.8 min in the control to 0.62–0.76 and 24.7–87.9 min in the treatments, respectively. The results of this study showed that the nanoparticles affected the solute transport and its parameters in the soil. Therefore, nanoparticles could be used to simplify the nutrients transport and leaching of salt and contaminants.

Predicting Solute Transport Parameters in Saturated Porous Media Using Hybrid Algorithm

This study aims to estimate the solute transport parameters in saturated porous media using a hybrid algorithm. In this study, the Physical Non-Equilibrium (PNE) model was used to describe the transport of solutes in porous media. A numerical solution for the PNE model is obtained using the Finite Volume Method (FVM) based on the Ttri-Diagonal Matrix Algorithm (TDMA). The developed program, written in Matlab, is capable to solve the advection-dispersion (ADE) and the PNE equations for the mobile -immobile (MIM)model with linear sorption isotherm. The Solute transport parameters, (immobile water content, mass transfer coefficient, and dispersion coefficient), are estimated using different algorithms such as the Levenberg-Marquardt algorithm (LM), genetic algorithm (GA), simulated annealing algorithm (SA). To overcome the limitations of deterministic optimization models which are rather unstable and divergent around a local minimum, a hybrid algorithm (GA+LM, SA+LM) permits to estimate of the solute transport parameters. Numerical solutions are verified using the experiments conducted by Semra (2003) which are about the transport of toluene through a column composed of impregnated Chromosorb grains at ambient temperature (20 °C) for three flow rates (1, 2 and 5ml/min). The results show that the hybrid algorithm (GA+LM, SA+LM) is more accurate than others (GA, SA, and LM). Comparing to the ADE model, The PNE with linear isotherm model gives a better description to the BeakThrough Curves (BTCs) with higher values of determination coefficient (R2) and lower values of Root Mean Square Error (RMSE). Also, the solute transport parameters tended to vary with the flow rate.

Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media

The dual-porosity structure of peat and the extremely high organic matter content give rise to a complex medium that typically generates prolonged tailing and early 50% concentration breakthrough in the breakthrough curves (BTCs) of chloride (Cl−) and other anions. Untangling whether these observations are due to rate-limited (physical) diffusion into inactive pores, (chemical) adsorption or anion exclusion remains a critical question in peat hydrogeochemistry. This study aimed to elucidate whether Cl− is truly conservative in peat, as usually assumed, and whether the prolonged tailing and early 50% concentration breakthrough of Cl− observed is due to diffusion, adsorption, anion exclusion or a combination of all three. The mobile-immobile (MiM) dual-porosity model was fit to BTCs of Cl− and deuterated water measured on undisturbed cores of the same peat soils, and equilibrium Cl− adsorption batch experiments were conducted. Adsorption of Cl− to undecomposed and decomposed peat samples in batch experiments followed Freundlich isotherms but did not exhibit any trends with the degree of peat decomposition and sorption became negligible below aqueous Cl− concentrations of ~310 mg L−1. The dispersivity determined by fitting the Cl− BTCs whether assuming adsorption or no adsorption were significantly different than determined by the deuterated water (p < .0001). However, no statistical differences in dispersivity (p = .27) or immobile water content (p = .97) was observed between deuterated water and Cl− when accounting for anion exclusion. A higher degree of decomposition significantly increased anion exclusion (p < .0001) but did not influence the diffusion of either tracer into the immobile porosity. Contrary to previous assumptions, Cl− is not truly conservative in peat due to anion exclusion, and adsorption at higher aqueous concentrations, but the overall effect of anion exclusion on transport is likely minimal.

Effect of Hydrocolloids on the Retrogradation of Lotus Seed Starch Undergoing an Autoclaving-Cooling Treatment.

The retrogradation properties of lotus seed starch (LS) blended with the hydrocolloids arabic gum (AG), carrageenan (CG), guar gum (GG), and xanthan (XN) were investigated undergoing an autoclaving-cooling treatment, a model for starch retrogradation acceleration. Compared with LS alone, LS-AG showed the increases in syneresis, tan δ (more solid-like behavior), bound water content and immobile water content, molecular weight, the intensity at 480 cm-1 in Raman spectra and the ratio of absorbance 1047 cm-1 /1022 cm-1 (R1047/1022 ) in FT-IR spectra. The results suggested that the addition of AG tended to promote the starch retrogradation, which was related to the increased molecular migration of free water, interactions of molecular starch chains, and the formation of ordered structures. The addition of CG, GG, or XN significantly decreased the syneresis, tan δ, the intensity at 480 cm-1 , and R1047/1022 values of LS, indicating the prevention of LS retrogradation. The effects of CG and XN on starch retrogradation mainly resulted from competition for water and the increased viscosity, as well as the coating effect on starch. The dominant viscosity of GG was the main factor that influenced starch retrogradation. These results showed not all hydrocolloids would retard starch retrogradation under autoclaving-cooling treatment, for which fine structures altered by different hydrocolloids were the key factors. PRACTICAL APPLICATION: Effects of hydrocolloids on the retrogradation of lotus seed starch were investigated undergoing an autoclaving-cooling treatment. The results will help guide the production and development of starchy foods having desirable properties by specific hydrocolloids during autoclaving-cooling process, especially to control starch retrogradation.

Evaluating Nonequilibrium Solute Transport through Four Soils of Pakistan using a HYDRUS Model and Nonparametric Indices

Core Ideas Soil structure with a large volume of small macropores has greater preferential transport. Nonparametric indices differentiated the soils with preferential transport. Chemical non‐equilibrium under unsaturated flow diminished fast in coarse blocky soil. Leaching experiments in soil under different saturations show inconsistent results regarding preferential flow, and therefore further investigations are needed. The comparative degree of non‐equilibrium flow of chloride (Cl) was evaluated using replicated large intact columns taken from two alluvial (Rawal, Typic Hapludalfs and Kotli, Entic Haplusterts) and two loess (Guliana, Udic Haplustalfs and Mansehra, Typic Hapludalfs) soils that differed in structure below 20 cm depth. Lithium chloride (3.5 mM) was pulsed with constant flows generated by heads 10, −10, −40 mm water; Cl breakthroughs were fit into a physical non‐equilibrium model with no sorption; and lithium (Li) breakthroughs (measured for the two loess soils) were fit into a physical and chemical non‐equilibrium model using HYDRUS‐1D. The Cl breakthrough curves were highly skewed, with immobile water contents in the range of 0.10 to 0.39 cm3 cm–3, indicating that physical nonequilibrium occurred under saturated flow as well as under unsaturated conditions. The nonparametric indicators (i.e., apparent dispersivity, the piston flow to Cl velocity ratio, the holdback factor, and the arrival time of the first 5% of Cl) indicated a greater strength of preferential flow in the Rawal and Guliana soils, which had more well‐connected pores than the Kotli and Mansehra soils, which had fewer macropores and dense aggregates. Lithium breakthrough occurred under chemical non‐equilibrium, which diminished with desaturation, especially in the Mansehra soil. There were two sources of preferential flow: (i) macropore flow under saturated conditions and (ii) bypass flow in the matrix due to regions of disconnected water under unsaturated conditions. The study results will help understand leaching potential of agro‐chemicals in similar soils.

Heat-induced gel properties of porcine myosin in a sodium chloride solution containing L-lysine and L-histidine

For the development of low sodium gelled meat products, the influence of L-Lys, L-His and L-Lys + L-His on the gelation behaviour and gel properties of porcine myosin in low (1 mmol/L), physiological (0.15 mol/L) and high (0.6 mol/L) NaCl solutions were studied. The dynamic rheological results indicated that the introduction of L-Lys or/and L-His increased the storage moduli change rate (ΔG′) of myosin at 1 mmol/L, 0.15 mol/L and 0.6 mol/L NaCl concentrations. The ΔG’ of myosin in the presence of L-Lys was higher than that in the L-His at 1mmol/L- 0.6 mol/L NaCl. A significant increase in gel hardness was observed in the presence of L-Lys or/and L-His (P < 0.05). Compared to the control, L-Lys or/and L-His remarkably reduced the cook loss and improved water-holding capacity of myosin gel at 1 mM NaCl (P < 0.05). Nuclear magnetic resonance (NMR) revealed a distinct increase in the immobile water content with a decrease in the free water in the presence of L-Lys or/and L-His. These findings demonstrated that the introduction of L-Lys or/and L-His have a positive effect on the thermal-induced gelation behaviour and enhanced water binding capacity, contributing to an improvement in the gel properties of myosin, particularly at low NaCl concentrations.

1H Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) Studies of Water Mobility in Dough Systems Containing Barley Flour

ABSTRACTThis study used 1H nuclear magnetic resonance (NMR) spin‐spin relaxation time (T2) and differential scanning calorimetric (DSC) measurements of unfreezable water content (UFW), to assess water behavior in freshly prepared (25°C), refrigerator‐stored (4°C, one day), or freezer‐stored (–35°C, one day) doughs containing 5, 10, or 30% whole grain, air‐classified β‐glucan‐diminished, and air‐classified β‐glucan‐enriched (BGB‐E) barley flours. Three populations of water were detected by NMR, depending on moisture content of dough, namely, tightly (T21, 2–5 msec), less tightly (T22, 20–50 msec), and weakly (T23, 100–200 msec) bound water. T22 peak was always detectable, and T22 peak time linearly correlated to moisture content of dough in a range of 0.7–2.0 g/g db (r = 0.99, P &lt; 0.05). Freezer storage showed less effect on water mobility in dough compared with refrigerator storage, whereas cooking and cool storage of cooked dough significantly decreased the water mobility (P &lt; 0.05). Adding barley flour steadily decreased the water mobility in dough, and the reduction was more significant with adding BGB‐E (P &lt; 0.05). Immobile water content was calculated by extrapolating T22 peak time versus total moisture content in dough and significantly correlated to the UFW content measured by DSC (r = 0.72, P &lt; 0.05).

Zeolite Effects on Immobile Water Content and Mass Exchange Coefficient at Different Soil Textures

The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg−1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θim), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (Dh). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl−1) in disturbed soil column. Cl−1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θim+ θm) and real pore water velocity calculated based on the mobile water content (θm) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg−1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg−1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg−1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θim and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater.

Interplay between resident and infiltrating water: Estimates from transient water flow and solute transport

► Interplay between resident (‘old’) and infiltrating (‘new’) water is investigated. ► Transient unsaturated water flow and solute transport measurements are presented. ► Piston-like displacement of old water is followed by mixing and entrainment. ► The flow regimes are governed by initial water content and soil particle grain size. This study investigates the interplay between resident (‘old’) water and incoming (‘new’) water in homogeneous, partially saturated sand undergoing infiltration, using a series of laboratory column experiments. It was hypothesized that old water pockets, defined both spatially and temporally, may be established during infiltration. This in turn, may affect the flow pattern of the infiltrating new water and/or contravene current geochemical reactions. Sands with three different particle size distributions and three initial water contents were employed. The upper end of each column was irrigated with water containing a conservative tracer, at three different flow rates, while free-drainage conditions were employed at the lower end. Analysis of the resulting 27 infiltration events was based on the Richards equation to describe fluid flow. Subsequently, the mobile-immobile model (MIM) was employed to describe the solute transport; the measurements were reproduced satisfactorily by these models. Results were further analyzed using mass balance considerations. Two regimes were identified: an initial piston-like mechanism that displaces old water, followed by a slow mixing/entrainment of the remaining old water. The relative contributions of these regimes appear to depend on the initial water content and the average grain size. In some cases, up to one-third of the old water fraction remained in the system following five flowthrough pore volumes. Comparison between the measured fractions of old water remaining in the system at the end of each infiltration event (i.e., after five flowthrough pore volumes) and the immobile water content (optimized from the MIM) relative to the initial water content, exhibited a significant linear correlation, with values about threefold higher for the optimized immobile fraction.

Vertical and Lateral Variations of Soil Immobile Water Fraction in Two Tillage Systems

A better understanding of water and solute movement in soils is crucial to limit the environmental impact of agricultural practices. The objective of this study was to compare preferential flow in soil due to mobile–immobile water partitioning at various depths in two tillage systems. Since 2000, an agricultural field has been divided into two plots cultivated using two tillage systems: conventional tillage with moldboard plowing (CT) and conservation tillage with disk harrowing (MT). The hydraulic conductivity at −1‐cm matric head, K−1, and the immobile water content of different soil compartments identified with a morphological description in each tillage system were measured using tension disk infiltrometers and a Br− tracer. Measurements were performed in 2005. A higher spatial variability of K−1 was observed in the CT plot than in the MT plot. The immobile water fraction at −1‐cm matric head under CT ranged from 0.039 to 0.947 with a mean of 0.524 (CV = 55%). Under MT, the immobile water fraction ranged from 0.216 to 0.882 with a mean of 0.631 (CV = 30%). Soil structure variation due to plowing was found to significantly influence the soil immobile water fraction under CT, while it was more uniform under MT at the 1‐m observation scale.