Exchangeable Hydrogen Research Articles

High strength “breathable” glycosilicone/Aloe vera polysaccharide-based gel dressing for efficient wound repair

Medical wound dressings are effective in protecting wounds, maintaining moisture, creating an optimal healing environment and accelerating wound healing. However, their deficiencies in mechanical properties, adhesion and prevention of adhesion to the wound bed have been identified as limiting factors for their therapeutic efficacy in wound healing. To address these issues, we prepared glycosilicone gel dressings consisting of hydrophobic polysiloxanes and highly hydrophilic polysaccharides via ester exchange and silicone hydrogen addition reactions. Silicone gel dressings exhibit skin-like “respiratory” properties, with good permeability to O2 and CO2. Additionally, elongation and other important parameters are similar to those of the skin, which provides a foundation for the application of silicone gels in the field of wound dressings. The introduction of Aloe vera polysaccharide (AP) results in the glycosilicone gel exhibiting certain mechanical properties, including a tensile strength of 0.35 MPa and an adhesion force of 10 N/m. Furthermore, a mouse model of total skin defect demonstrated that the wound healing rate of the mice on the 12th day was 98 %, which effectively promotes wound healing. Consequently, the glycosilicone gel is anticipated to be an optimal wound dressing.

Do exchangeable hydrogens affect the evaluation of partial mycoheterotrophy in orchids? Insights from δ2H analysis in bulk, α-cellulose, and cellulose nitrate samples.

To evaluate the nutritional modes of orchids associated with 'rhizoctonia' fungi, analyses of hydrogen (δ2H), carbon (δ13C), and nitrogen (δ15N) stable isotope ratios are usually adopted. However, previous studies have not fully accounted for exchangeable hydrogens, which could affect these evaluations. Here, we performed standard δ13C, δ15N, and δ2H analyses on bulk samples. Additionally, we conducted δ2H analysis on α-cellulose and cellulose nitrate samples to investigate whether the heterogeneity of exchangeable hydrogens among plant species influences the assessment of nutritional modes. The δ2H of orchids were consistently higher than those of surrounding autotrophic plants, irrespective of the three pretreatments. Although the rhizoctonia-associated orchid exhibited lower δ13C, its δ2H was higher than those of the autotrophs. Notably, among all response variables, δ15N and δ2H exhibited high abilities for discriminating the nutritional modes of rhizoctonia-associated orchids. These results indicate that a time-efficient bulk sample analysis is an effective method for evaluating plant nutritional modes, as the heterogeneity of exchangeable hydrogens does not significantly impact the estimation. Using δ15N and δ2H benefits the assessment of partial mycoheterotrophy among rhizoctonia-associated orchids.

Numbers of Exchangeable Hydrogens from LC-MS Data of Heavy Water Metabolically Labeled Samples.

Labeling with deuterium oxide (D2O) has emerged as one of the preferred approaches for measuring the synthesis of individual proteins in vivo. In these experiments, the synthesis rates of proteins are determined by modeling mass shifts in peptides during the labeling period. This modeling depends on a theoretical maximum enrichment determined by the number of labeling sites (NEH) of each amino acid in the peptide sequence. Currently, NEH is determined from one set of published values. However, it has been demonstrated that NEH can differ between species and potentially tissues. The goal of this work was to determine the number of NEH for each amino acid within a given experiment to capture the conditions unique to that experiment. We used four methods to compute the NEH values. To test these approaches, we used two publicly available data sets. In a de novo approach, we compute NEH values and the label enrichment from the abundances of three mass isotopomers. The other three methods use the complete isotope profiles and body water enrichment in deuterium as an input parameter. They determine the NEH values by (1) minimizing the residual sum of squares, (2) from the mole percent excess of labeling, and (3) the time course profile of the depletion of the relative isotope abundance of monoisotope. In the test samples, the method using residual sum of squares performed the best. The methods are implemented in a tool for determining the NEH for each amino acid within a given experiment to use in the determination of protein synthesis rates using D2O.

Soil organic matter and total nitrogen as key driving factors promoting the assessment of acid-base buffering characteristics in a tea (Camellia sinensis) plantation habitat.

The issue of soil acidification in tea plantations has become a critical concern due to its potential impact on tea quality and plant health. Understanding the factors contributing to soil acidification is essential for implementing effective soil management strategies in tea-growing regions. In this study, a field study was conducted to investigate the effects of tea plantations on soil acidification and the associated acid-base buffering capacity (pHBC). We assessed acidification, pHBC, nutrient concentrations, and cation contents in the top 0-20cm layer of soil across forty tea gardens of varying stand ages (0-5, 5-10, 10-20, and 20-40years old) in Anji County, Zhejiang Province, China. The results revealed evident soil acidification due to tea plantation activities, with the lowest soil pH observed in tea gardens aged 10-20 and 20-40years. Higher levels of soil organic matter (SOM), total nitrogen (TN), Olsen phosphorus (Olsen-P), available iron (Fe), and exchangeable hydrogen (H+) were notably recorded in 10-20 and 20-40years old tea garden soils, suggesting an increased risk of soil acidification with prolonged tea cultivation. Furthermore, prolonged tea cultivation correlated with increased pHBC, which amplified with tea stand ages. The investigation of the relationship between soil pHBC and various parameters highlighted significant influences from soil pH, SOM, cation exchange capacity, TN, available potassium, Olsen-P, exchangeable acids (including H+ and aluminum), available Fe, and available zinc. Consequently, these findings underscore a substantial risk of soil acidification in tea gardens within the monitored region, with SOM and TN content being key driving factors influencing pHBC.

Heat-induced structural and chemical changes to a computationally designed miniprotein.

The de novo design of miniprotein inhibitors has recently emerged as a new technology to create proteins that bind with high affinity to specific therapeutic targets. Their size, ease of expression, and apparent high stability makes them excellent candidates for a new class of protein drugs. However, beyond circular dichroism melts and hydrogen/deuterium exchange experiments, little is known about their dynamics, especially at the elevated temperatures they seemingly tolerate quite well. To address that and gain insight for future designs, we have focused on identifying unintended and previously overlooked heat-induced structural and chemical changes in a particularly stable model miniprotein, EHEE_rd2_0005. Nuclear magnetic resonance (NMR) studies suggest the presence of dynamics on multiple time and temperature scales. Transiently elevating the temperature results in spontaneous chemical deamidation visible in the NMR spectra, which we validate using both capillary electrophoresis and mass spectrometry (MS) experiments. High temperatures also result in greatly accelerated intrinsic rates of hydrogen exchange and signal loss in NMR heteronuclear single quantum coherence spectra from local unfolding. These losses are in excellent agreement with both room temperature hydrogen exchange experiments and hydrogen bond disruption in replica exchange molecular dynamics simulations. Our analysis reveals important principles for future miniprotein designs and the potential for high stability to result in long-lived alternate conformational states.

Performance Enhancement of Silicone Rubber Using Superhydrophobic Silica Aerogel with Robust Nanonetwork Structure and Outstanding Interfacial Effect.

The application of high-performance rubber nanocomposites has attracted wide attention, but its development is limited by the imbalance of interface and network effects caused by fillers. Herein, an ultrastrong polymer nanocomposite is successfully designed by introducing a superhydrophobic and mesoporous silica aerogel (HSA) as the filler to poly(methyl vinyl phenyl) siloxane (PVMQ), which increased the PVMQ elongation at break (∼690.1%) by ∼9.3 times and the strength at break (∼6.6 MPa) by ∼24.3 times. Furthermore, HSA/PVMQ with a high dynamic storage modulus (G'0) of ∼12.2 MPa and high Payne effect (ΔG') of ∼9.4 MPa is simultaneously achieved, which is equivalent to 2-3 times that of commercial fumed silica reinforced PVMQ. The superior performance is attributed to the filler-rubber interfacial interaction and the robust filler-rubber entanglement network which is observed by scanning electron microscopy. When the HSA-PVMQ entanglement network is subjected to external stress, both the HSA and bound-PVMQ chains are synergistically involved in resisting structural evolution, resulting in the maximized energy dissipation and deformation resistance through the desorption of the polymer chain and the slip/interpenetrating of the exchange hydrogen bond pairs. Hence, highly aggregated nanoporous silica aerogels may soon be widely used in the application of reinforced silicone rubber or other polymers shortly.

An innovative geothermal based multigeneration plant: Thermodynamic and economic assessment for sustainable outputs with compressed hydrogen

In the net-zero emissions strategy adopted to struggle global warming and environmental difficulties, the effective utilization of clean energy sources is important. In this framework, geothermal sources are an important renewable energy sources and offer many advantages. In the developed new research, a geothermal energy-supported combined configuration is considered and proposed for sustainable hydrogen, power, freshwater, hot water, and drying. In this system, an exhaustive thermodynamic examination, -energy, exergy efficiency, and exergy destruction-, as well as an economic analysis are carried out. This newly designed configuration comprises a flash-geothermal circuit, a transcritical CO2 fluid Rankine plant (tRC), a dryer, a multi-effect desalination (MED) component, and a Proton exchange membrane (PEME) and hydrogen storage units. In light of the analysis outcomes, the power generation load of the system is 1587 kW and the hydrogen quantity is calculated 0.00223 kg/s. In addition, the thermodynamic performance indicators, which are energetic and energetic performance of the tRC are determined as 10.91% and 41.68%. Moreover, the energetic efficiency of the modeled configuration is determined to be 23.18%, whereas the exergetic performance indicator is found to be 28.57%. Regarding the economic cost evaluations, the total cost of this model is calculated as 171.5 $/h.

Recyclable water-modified deep eutectic solvents for removal of multiple heavy metals from soil

Removing heavy metals from soil has always been a challenge in terms of safety and effectiveness. Deep eutectic solvents (DESs) are recognized as environmentally friendly reagents with great potential in the removal of heavy metals from soil. In this study, water was introduced as a third component to form new ternary deep eutectic water solvents (DEWSs) to improve their performance. The removal capacity, applicable conditions and mechanisms of sixteen DEWSs for heavy metals were systematically investigated. Experimental results showed that the presence of water significantly enhanced the removal efficiency of three DESs (Choline chloride plus Urea, DEU; Choline chloride plus l-lactic acid, DELA; and Choline chloride plus Ethylene glycol, DEEG) for heavy metals. However, as the molar ratio of water increased, the eutectic systems in the DEWSs weakened and eventually disappeared. Under optimum conditions, DEWLA7 (DELA : H2O = 2 : 8) showed the highest removal rate for cadmium, lead, copper and zinc, which were 43.42%, 94.73%, 90.72% and 96.44%, respectively. Hydrogen bonding, adsorption of oxygen functional groups, exchangeable hydrogen substitution, changes in viscosity properties and co-precipitation all contributed to the removal of heavy metals by DEWLA7. Notably, DEWLA7 had no significant effect on the content of major minerals and nutrients in the soil. Furthermore, DEWLA7 proved to be reusable for soil washing, and still retains a high removal rate of 37.32%–83.66% after multi-stage filtration treatment. Therefore, DEWLA7 was an unexplored and excellent soil washing agent with great potential in economic and social benefits.

Konstantin Gedroiz (1872–1932)—the Initial Studies of Soil Colloid Chemistry and Soil Salinity

We present a review of the life and scientific legacy of the founder of soil colloid chemistry Konstantin Gedroiz. The phenomenon of absorption was first studied in the mid-1800s, and Gedroiz started working on base exchange and absorption in soils in 1906. Based on the general pattern of cation exchange reactions, he proposed the concept of “absorption capacity” and “soil absorption complex”, developed ideas about exchange acidity and the rate of exchange reactions, revealed the unique role of absorbed sodium and potassium in soil processes, and proposed the theory of the accumulation of sodium due to exchange reactions. He was one of the first to classify soil on the basis of the absorbing complexes and cations, which was a new approach in pedology. He used the climate classification of soils, and described Podzols, Laterites, and Chernozems in terms of their absorbing complexes and cations. The system of classification worked for mature soils in which pedogenic processes had proceeded to such an extent that the profile characteristics reflected a climatic region, but was less effective in alluvial soils and eroded soils. His studies established the connections between chemical and physical processes and the morphology of soils. He studied the evolution of saline soils from a chemical point of view, which led to the practical recommendations for chemical reclamation of Solonetz and liming of acidic soils. Gedroiz’s work was groundbreaking but insufficiently known outside Russia until his books have been translated into English and German in the late 1920s. The soil microbiologist Selman Waksman in the 1925 translated 11 of his papers into English, and the United State Department of Agriculture distributed copies of these translations. In 1927 a textbook on chemical analysis, “Die chemische Bodenanalyse”, was published; in 1930 the books “Der adsorbierende Bodenkomplex und die adsorbierten Bodenkationen als Grundlage der genetischen Bodenklassification” and “On the Problem of exchangeable Hydrogen and exchangeable Aluminium in acid soils”, a 1931 – “Die Lehre vom Adsorptionsvermögen der Böden”.

Пространствено вариране на физикохимичните свойства на почвите от Ботевградската котловина

The aim of the present study is a spatial analysis and assessment of the main physicochemical properties of the soils in Botevgrad Valley. The soil samples were taken along a pre-selected grid to cover the areas selected for research as uniformly as possible. The data were interpolated using the geostatistical methods of kriging and variogram analysis. The soils have relatively favourable physicochemical properties, such as the cation sorption capacity with values from 10.80 to 24.50 mequ/100 g of soil. The basic cations, such as calcium and magnesium, dominate anywhere, and those with acidic functions, such as exchangeable aluminium and hydrogen, have minimal values. The base saturation is almost above 50%, and the soils are defined as Eutric. Soil reaction also varies from strongly acidic to slightly alkaline.

Development of High Durable Pore-Filling Anion Exchange Membranes for Water Electrolysis Application

Water electrolyzer is a device that converts renewable electrical energy into environmentally friendly chemical energy, hydrogen. Water electrolysis is mainly categorized into proton exchange membrane water electrolysis (PEMWE) and anion exchange membrane water electrolysis (AEMWE). Non-precious electrocatalysts and hydrocarbon-based polymeric membranes are used for two different systems. It is advantageous for AEMWE in terms of cost. However, low current density and chemical stability for current anion exchange membrane technology (AEM) restricts early market penetration. Thus, thedevelopment of low resistance and high durable AEMs is of importance. In this study, superior ion conductivity and high durable pore-filling AEMs were developed for AEMWE. Pore-filling AMEs with different contents of crosslinking monomers were prepared by the monomers using chemically stable anion exchangeable functional groups in a porous polyethylene(PE) substrate. Properties of the AEMs were characterized through areal resistance, ionic conductivity, ion exchange capacity, water uptake, swelling ratio, mechanical strength and hydrogen crossover. In addition, AEMWE performance and durability tests were also conducted. Acknowledgments This research was supported in part by Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253), Rural Development Administration, Republic of Korea and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Nuclear Magnetic Resonance Detection of Hydrogen Bond Network in a Proton Pump Rhodopsin RxR and Its Alteration during the Cyclic Photoreaction.

Hydrogen bond formation and deformation are crucial for the structural construction and functional expression of biomolecules. However, direct observation of exchangeable hydrogens, especially for oxygen-bound hydrogens, relevant to hydrogen bonds is challenging for current structural analysis approaches. Using solution-state NMR spectroscopy, this study detected the functionally important exchangeable hydrogens (i.e., Y49-ηOH and Y178-ηOH) involved in the pentagonal hydrogen bond network in the active site of R. xylanophilus rhodopsin (RxR), which functions as a light-driven proton pump. Moreover, utilization of the original light-irradiation NMR approach allowed us to detect and characterize the late photointermediate state (i.e., O-state) of RxR and revealed that hydrogen bonds relevant to Y49 and Y178 are still maintained during the photointermediate state. In contrast, the hydrogen bond between W75-εNH and D205-γCOO- is strengthened and stabilizes the O-state.

Adsorption and migration of ammonia nitrogen in sediments in the presence of SiO2 and HA colloids

The release of internal pollutants in shallow lakes is a widely concerning environmental issue. Colloids widely existing in eutrophic shallow lakes will affect the release and migration of pollutants. In this context, the different effects of two colloids [humic acid (HA) and silica (SiO2)], either individual or in coexistence, on the adsorption and migration of ammonia nitrogen (NH4+-N) in sediments under different ionic strengths (IS) were analyzed, through a series of batch and column experiments. It was found that, under a relatively low IS condition (1 mM Na+), SiO2 colloids greatly enhanced the mobility of NH4+-N in sediments. With IS increased (20 mM Na+), the presence of colloids exhibited an impeding effect on the mobility of NH4+-N due to colloidal flocculation and precipitation. While HA colloids largely suppressed the mobility of NH4+-N in sediments under either low or high IS conditions. HA colloids are more likely to form aggregates and have more adsorption sites than SiO2 colloids. In the NH4+-N–SiO2–HA system, HA colloids also showed a retardant effect on the transport of both SiO2 colloids and NH4+-N, and the retardant effect increased with the increase of HA colloid concentration. Exchange coordination and hydrogen bond force, as well as the decreased stability of the colloid system, played an important role in such a retardant effect, which consequently resulted in more NH4+-N adsorption. The transport of colloids in the NH4+-N–colloids co-transport system can be successfully described by Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. In addition, with an increase of IS, NH4+-N transport was enhanced because of competitive adsorption of the cations and NH4+-N on colloids and the porous medium. These results implied that abundant HA colloids and low ion concentration can reduce the risk of NH4+-N release and migration in sediments and consequently its exchange flux across the sediment-water interface.

The early impact of mixed canopies with Norway spruce, European beech and silver fir on a new forest floor

The character of pure or mixed forest canopies and their litterfalls contribute to different forest-floor properties. These organic layers and also subjacent topsoil were studied at three study sites covered by mixed treatments such as beech–spruce, beech–fir, spruce–fir and two monospecific beech and spruce treatments. The age of the forest stands ranged from 11 to 15 years when sampled. All study sites were used as meadows when afforested; therefore, the forest floors were new, and the A-horizon topsoil properties were not influenced by older humus inherited from previous forest generations. The mineral soil was likely affected by different levels of former fertilization, which resulted in differences among the study sites. The early-developed forest floors showed differences between the treatments with beech and the others. The topsoil below beech with spruce had more nitrogen, oxidizable carbon and cations of exchangeable hydrogen as well as pH showing more acidic conditions and lower contents and saturation of base cations. Pure beech had more phosphorus. The nutrient pools did not differ among the treatments; significantly more matter was found below the oldest stands on the first afforested site, which also increased nutrient pools.

Determination of Binding Sites on Trastuzumab and Pertuzumab to Selective Affimers Using Hydrogen-Deuterium Exchange Mass Spectrometry.

Hydrogen-deuterium exchange mass spectrometry (HDX-MS) is a method to probe the solvent accessibility and conformational dynamics of a protein or a protein-ligand complex with respect to exchangeable amide hydrogens. Here, we present the application of HDX-MS to determine the binding sites of Affimer reagents to the monoclonal antibodies trastuzumab and pertuzumab, respectively. Intact and subunit level HDX-MS analysis of antibody-affimer complexes showed significant protection from HDX in the antibody Fab region upon affimer binding. Bottom-up HDX-MS experiments including online pepsin digestion revealed that the binding sites of the affimer reagents were mainly located in the complementarity-determining region (CDR) 2 of the heavy chain of the respective antibodies. Three-dimensional models of the binding interaction between the affimer reagents and the antibodies were built by homology modeling and molecular docking based on the HDX data.

Combined Utilization of Chinese Milk Vetch, Rice Straw, and Lime Reduces Soil Available Cd and Cd Accumulation in Rice Grains

Cadmium (Cd) pollution poses a growing threat to rice production in acidic paddies. In south China, a common agricultural practice involves the combined utilization of Chinese milk vetch (M) and rice straw (R). However, it is unclear how the addition of lime to these amendments affects Cd bioavailability and accumulation in soil. Control (CK), chemical fertilizer (F), Chinese milk vetch + rice straw + chemical fertilizer (MRF), and Chinese milk vetch + rice straw + chemical fertilizer + lime (MRFL) treatments were applied to develop a kind of green, efficient, and practical amendment for acidic paddies. We conducted a microplot experiment to explore Cd immobilization in paddy soil and the Cd content in rice grains with these treatments. The results showed that compared with F, the rice Cd in the MRF and MRFL treatments were significantly decreased by 51.7% and 65.2% in early rice and 23.0% and 43.3% in late rice, respectively. Both the MRF and MRFL treatments significantly reduced soil available Cd and weak acid-extractable cadmium (Aci-Cd) concentrations and increased soil organic matter (SOM), exchangeable cation concentrations, and pH, which converted Cd into a stable form in soil. In addition, the MRF and MRFL treatments increased soil pH value by reducing soil exchangeable hydrogen ion concentration (E-H). Additionally, recombination of Cd forms was the primary factor in the reduction in available Cd concentration according to partial least squares path modeling (PLS-PM) analysis. The Cd concentration of rice grains was primarily associated with soil available Cd, soil pH value, and SOM. Overall, these results provide useful data and novel insights into reducing rice grain Cd in south China.

Reproducible measurements of the δ2H composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system

Non-exchangeable hydrogen-isotope (δ2Hn) measurements of complex organic samples are used in forensics to determine sample authenticity, traceability, and provenance. However, δ2Hn assays of organics are usually complicated by uncontrolled “exchangeable hydrogen” and residual moisture contamination; hence, δ2Hn assays are persistently incomparable amongst laboratories. We introduce a revised technical solution (UniPrep2) to control hydrogen-isotope exchange and for robust online sample drying and vapour equilibration. The UniPrep2 device is coupled to a high-temperature thermochemical elemental analyser and continuous-flow isotope-ratio mass spectrometer. This technical solution empowers isotope analysts to:•Conduct reproducible controlled vapour equilibrations of complex organic samples and standards to determine the δ2Hn values by controlling hydrogen-isotope exchange.•Conduct online vacuum-oven evacuation with extensive helium drying without exposure to air to reabsorb or exchange hydrogen with ambient water vapour.The protocol describes the operation of the UniPrep2 device and the step-by-step procedures needed to obtain accurate and precise δ2Hn values for a wide range of organic sample types. Two analytical approaches are described in detail; the Dual-Vapour Equilibration (DVE) approach, intended for determining δ2Hn for a complex organic environmental sample where matrix equivalent H isotope reference materials are not available, and the Comparative Equilibration (CE) approach, which is intended for routine high-throughput analyses of complex organic samples where at least two matrix-equivalent organic isotope reference materials with consensus δ2Hn values are being used. These standard operating procedures are envisioned to be a sound basis for advancing hydrogen-isotope analysis for different organic environmental matrices and studies.

Dynamics of Acidity Component of the Soils as Influenced by Liming in Upper Brahmaputra Valley Zone of Assam, India

An incubation study was conducted to investigate the effect of lime (CaCO3 )on the acidity components in Upper Brahmaputra Valley Zone (UBVZ) of Assam. Fourteen(14) geo-referenced soil samples were collected from Sibsagar and Jorhat districts of Assam. Soils were treated with 3 different doses of lime viz. 10 per cent Lime Requirement (LR10), 25 per cent Lime Requirement (LR25) and 50 per cent of Lime Requirement (LR50) and initial properties were recorded before liming. Samples were incubated in laboratory at different period of time viz. 15, 30, 60 and 90 days after liming (DAL) with moisture content at Field Capacity (0.33 bar). At four different intervals, soils were analysed for soil acidity components viz. total acidity, exchange acidity, exchangeable Al3+ and exchangeable H+. The soil of Upper Brahmaputra Valley Zone (UBVZ) of Assam were highly acidic to moderately acidic, sandy loam to silt loam in texture with high OC content ranged from 0.72 to 2.59%. The Cation Exchange Capacity (CEC) value ranged from 7.8 to 14.2 cmol (p+)/ kg. Application of lime brought about mark decreased in acidity components viz. total acidity, exchange acidity, exchangeable aluminium and exchangeable hydrogen. Soil acidity components recorded highest decreased at 90 DAL @ LR50 and decreased started from 15 days onwards. The findings of the investigation showed that liming @ LR10 was found effective in reducing soil acidity. The residual effect of lime was found persisting till 90 days. However, the magnitude of lime was increasing with increase in application of lime@ from LR10 to LR25 and to LR50.

Soil Acidity and its Distribution in Laterite Soils of Northern Kerala: A Descriptive Analysis

Soil acidity is one of the major constraints of crop production in tropical soils. A study was conducted to examine different forms of soil acidity, contribution of each fraction to total acidity and distribution of exchangeable Al+3, exchangeable H+ detrital laterite rice wetlands of Kerala. Among the series, the Kalikkadavu series reported the highest exchangeable acidity with a mean of 1.66 ± 0.23 meq/100g at a depth of 0-15 cm. Soils from Angadipuram series showed high values for exchangeable hydrogen with a mean of 0.71 ± 0.87 meq/100g and a range of 0.2- 3 meq/100g. Kalikkadavu series reported a high value for exchangeable hydrogen with a mean value of 1.29 ± 0.23 meq/100 g. Regarding potential acidity, Nanminda series reported the highest with a mean value of 40.2 meq/100g. Descriptive statistics of pH dependent acidity data revealed highest acidity for Nanminda series in surface layer with a mean value of 39.27 ± 1.77 meq/100g while in subsurface soils, Arathil series has reported the highest with a mean value of 32.21 ± 3.28 meq/100g. From the paired t-test analysis, significant variations of potential acidity and pH-dependent acidity were observed across surface and subsurface while exchangeable acidity, exchangeable Al+3, exchangeable H+ have shown non-significant variation.Hence, we recommend a proper soil management system that lowers the surface and subsoil acidity in low-pH soil. Again, for best effects in terms of biomass production and economic crop yields, amelioration of soil acidity should be followed by optimum plant nutrient inputs.

Method Validation for Determination of Exchangeable Acidity in Soils

The laboratory analyzed and determined the same type of forest soil samples at three content levels. The relative standard deviations of exchangeable acidity, exchangeable hydrogen and exchangeable aluminum in the soil were 2.26%, 2.31%, 1.72%, 10.06%, and 4.61%, respectively. %, 5.12%, 4.02%, 7.70%, 5.42%, and the actual samples were verified by the experiment, and the relative deviations of the parallel samples of exchangeable acidity, exchangeable hydrogen and exchangeable aluminum of soil samples were 1.30%, 1.03%, and 1.75%, respectively. All of them meet the determination requirements of "Determination of Soil Exchangeable Acidity by Potassium Chloride Extraction - Titration Method" (HJ 649-2013) when the measured value is <=10.0 mmol/kg, and the maximum allowable relative deviation is ±20%. It shows that the laboratory has the ability to detect the exchangeable acidity in soil.