Base Cations Research Articles

Phosphorus fractions and their relationships with soil chemical attributes in an integrated crop-livestock system under annual phosphates fertilization

The main factors affecting phosphorus (P) availability in soils are mineralogy, acidity, and concentration of elements in the soil solution. Moreover, P fertilizer sources and amounts can affect P cycling and adsorption of this element on colloids. In this research, we hypothesized that the use of phosphate sources of different solubilities can alter soil P adsorption process, due to chemical compositions of these sources and, in ICLS, the soil-plant-animal system can change the P forms distribution on soil profile and its interactions with the soil chemical attributes. To examine these hypotheses, a field experiment was conducted over 5 years, under a Haplic Cambisol, in an incomplete factorial scheme, with the treatments being composed of three P sources (triple superphosphate, rock phosphate—Arad and magnesium thermophosphate), three doses of total P2O5 (60, 120, and 180 kg ha−1) plus a treatment without application of phosphate fertilizer. Phosphate applications occurred annually, broadcast without incorporation, at the time of sowing the annual winter forage, in a crop rotation system that included pasture in autumn-winter and grain crops in spring-summer. Soil samples were collected at depths of 0 to 5, 5 to 10, 10 to 15, 15 to 20, and 20 to 30 cm and evaluated by Hedley P fractionation and the soil chemical attributes were quantified. The use of different phosphates applied broadcast without incorporation did not influence the concentrations of soil P fractions over a 5 year study. Phosphate fertilizer doses above 120 kg ha−1 of total P2O5 increased moderately labile and non-labile P fractions. The highest concentration of labile P was found up to 15 cm soil depth. It was found that P lability is strongly associated with calcium and total organic carbon concentrations in the soil profile. High concentrations of basic cations and sulfate in the soil solution increased moderately labile and non-labile P fractions. The complexity of ICLS interactions to maintain phosphorus dynamics in the soil was shown to be an intricate P release/adsorption process associated with soil chemical attributes.

Base Cation Mobility in Vineyard Soils of the Colli Albani Volcanic District (Central Italy)

The quality of the Colli Albani volcanic soils has certainly contributed to the vine cultivars hence the name of one of the oldest wines (i.e., Alban wine). The alkali up to 15 wt%, SiO2 ≤ 52 wt% and the emplacement at high temperature (≤ 600 °C) are the bedrock features that have deeply influenced the soil-forming processes in the vineyards. However, the peculiar features of the Colli Albani soils are not well known. Field survey and textural, mineralogical, and chemical data obtained with SEM, EMP, XRD, and ICP-OES were used to characterize the vineyard soils of the Colli Albani. Leucite (Lct)-bearing soils and quartz (Qz)-bearing soils occur in the studied vineyard. The Qz-bearing soils represent more weathered volcanic material, depleted in primary minerals and enriched in clays, which show a lower cation exchange capacity (CEC) than the Lct-bearing soils. CEC is a misleading definition for the Colli Albani soils because the base cation mobility in the vineyard is independent from clay mineral enrichment in the soil. Actually, the release of K, Na, Ca, and Mg depends by (i) the complete dissolution of leucite and analcime, (ii) the oxy-reaction affecting the phlogopite, which releases K + Mg, and (iii) the incongruent dissolution of clinopyroxene characterized by the “gothic texture.” This texture highlights the capacity of clinopyroxene to release Ca and Mg in volcanic soils. Quantification of the texture and abundance of the primary minerals are mandatory for the management of the vineyard soils in the Colli Albani and, in general, it is significative for the vineyards in volcanic areas.

Base cations release in soils along the 127‐year Hailuogou glacial retreat chronosequence

AbstractAt the Hailuogou glacial retreat chronosequence, a mature forest has surprisingly fast developed in ∼120 yr, although the glacial debris is dominated by nutrient‐poor granite with a small contribution of carbonate minerals. In previous work, we hypothesized that the fast vegetation development is synchronized with initial fast carbonate weathering followed by slow silicate weathering. To test this hypothesis, we (a) characterized the composition of the glacial debris to elucidate the sources of base cations and (b) determined the base cation release kinetics from topsoils (0–10 cm) along the chronosequence with a weathering experiment at a constant pH value (pHstat). Besides granitic rocks, the glacial debris contained some meta‐sedimentary and meta‐volcanic calc‐silicate rocks, amphibolite, mica schist, and quartzite. Although the total Ca concentration of the glacial debris was only about double that of Mg, K, and Na, during the 1st day of the pHstat experiment, the released mass of Ca was >10 times higher than that of Mg and K, and even about 100 times higher than that of Na. The size of the fast‐reacting Ca‐carbonate pool decreased quickly in the first approximately 40 yr, after which a slow‐reacting Ca‐silicate pool matched the fast‐reacting pool with a size of 1.9 ± 0.6 g kg–1 Ca. In contrast, for Mg, K, and Na the slow‐reacting pool dominated from the beginning, suggesting that these elements mainly originated from silicate weathering. Our findings support the view that the well‐synchronized interplay between carbonate and silicate weathering facilitated the fast vegetation succession.

Lithological controls on soil geochemistry and clay mineralogy across Spodosols in the coastal temperate rainforest of southeast Alaska

The interaction of similar soil forming factors with different parent materials determines soil chemical weathering, influencing soil processes and properties. In the coastal temperate rainforests of southeast Alaska, Spodosols is the dominant soil order in well-drained parent materials regardless of the lithology. Yet, the role of lithology on chemical weathering, base cation depletion, and mineral transformation during pedogenesis remains elusive. Here, we established a lithosequence comprised of soils derived from tonalite, phyllite, slate, and metavolcanic rocks to test the hypothesis that despite the soils in southeast Alaska presenting similar taxonomy and morphology, the influence of lithology in chemical weathering intensity and mineralogy can be detected. We evaluated physicochemical properties, clay mineralogy, Fe-Al oxides, chemical weathering, and elemental mass balance on eleven Spodosols sampled along the lithosequence. We also propose a new weathering index, the Weathering Index for Spodosols (WISP), suitable to evaluate the weathering degree of soils with Al mobility and base-rich parent materials. This index fills a gap in traditional weathering indices that uses Al as an immobile element and/or does not evaluate the leaching of main base cations. We found the pedons across the lithosequence expressed similar physicochemical properties, with predominantly thick profiles, presenting andic properties, relatively thick spodic horizons, and thin E horizons. Podzolization imposed similar mineral transformation trends, mainly dissolution of chlorite, mica alteration to interstratified mica-vermiculite, and formation of smectite in E horizons. Kaolinite was detected in the soils from all lithologies, but only in trace amounts in phyllite soils. Fe oxides depth distribution was similar but with a higher concentration in the slate (44.5 ± 4.2 g/kg), followed by metavolcanic (31.6 ± 4.0 g/kg), phyllite (27.9 ± 3.8 g/kg), and tonalite soils (19.9 ± 5.7 g/kg) and predominantly as organometallic complexes (extracted by Na-pyrophosphate). The stronger weathering of chlorite and mica in the E horizons was reflected in larger losses of Mg and K, while Ca and Na were more depleted in the spodic horizons, suggesting plagioclase weathering. Slate soils were the most depleted in base cations, followed by phyllite, tonalite, and metavolcanic soils. The more depleted status of slate soils was supported by the higher WISP values (WISP = 62), followed by phyllite (WISP = 55), tonalite (WISP = 53), and metavolcanic soils (WISP = 45). Our results demonstrated that lithology controlled elemental depletion intensities, Fe oxide concentrations, and partially the clay fraction mineralogy in addition to podzolization acting as a dominant pedogenic process across all sites. These findings advance our understanding of the role of lithology on soil mineralogy/geochemistry that impacts critical soil functions, such as the soil carbon cycle, elemental fluxes, organo-mineral interactions, and solid-solution reactions.

Seasonally variable interactions between dissolved organic matter and mineral particles in an agricultural river

Streams and rivers form an important link in the global carbon cycle by transporting and transforming large amounts of carbon imported from terrestrial ecosystems to the oceans. Since streams in agricultural areas often experience increased concentrations of suspended mineral particles from soil erosion, they are important sites where dissolved organic carbon (DOC) may be adsorbed to particles and retained in the sediment. As the extent of adsorption varies with the molecular composition of dissolved organic matter (DOM), which is seasonally variable, we expect also the fraction of organic material that adsorbs to mineral particles to fluctuate over time. We sampled the agriculturally impacted River Fyrisån (Sweden) monthly during 1 year, and measured DOC concentration and DOM composition based on several optical properties. At each sampling occasion, we estimated the potential for adsorption by exposing the samples to a reference clay. The potential for adsorption was greatest when riverine DOM had the most terrestrial character, as this fraction of the DOM pool was selectively adsorbed to clay surfaces. The extent of adsorption was negatively related to the concentration of base cations, most notably calcium. We suggest that the observed relationships between the potential for adsorption, DOM composition and base cations are linked by discharge. A bioavailability test at one sampling occasion suggested that DOM remaining after exposure to clay particles was more biodegradable. This implies that adsorption may alter the degradation potential of DOM remaining in solution, which could have far reaching effects on the fate of organic carbon.

Impact of liming on extractable phosphorus, exchangeable base cations, and effective cation exchange capacity of eastern Free State soils

Soil acidity can adversely affect wheat production in the eastern Free State, South Africa. Liming of the soils is therefore essential. The aim of this study was to establish whether extractable phosphorus (P), exchangeable calcium (Ca), magnesium (Mg) and potassium (K) concentrations and cation ratios remained within recommended ranges after liming. Incubation and field studies were done on soils of wheat fields at Kestell, Fouriesburg, Prinsloo and Melrose in the eastern Free State, South Africa. Lime was applied at different rates to induce soil acidity ranges for determination of Bray 1 extractable P and ammonium acetate (NH4OAc) exchangeable Ca, Mg and K concentrations. Cation ratios (Ca:Mg, Mg:K and (Ca + Mg):K) and effective cation exchange capacity (ECEC) were also calculated. Apart from the Prinsloo soil, liming decreased extractable P concentration only in the incubation study. In the incubation and field studies exchangeable Ca and Mg concentrations increased while exchangeable K concentration remained unchanged. Despite liming of the soils, exchangeable Ca and Mg concentrations at Kestell and Fouriesburg were still less than the required thresholds. The Ca:Mg ratio decreased at both sites while the Mg:K and (Ca + Mg):K ratios increased with liming. Liming increased ECEC of all soils at all four sites. Our results show that liming does not always result in the recommended cation levels required for soil fertility.

The driving factors and buffering mechanism regulating cropland soil acidification across the Sichuan Basin of China

Cropland soil has a higher acidification risk, with the driving factors and the soil buffering capacity controlling the degree of soil acidification. However, the relative importance of the main driving factors at broad geographic scales remains unclear, and the evidence on the acid-buffering process is rarely examined by large-scale observations. Using 4101 soil samples obtained in 1980s and 4348 soil samples collected in 2010s, this study explored topsoil pH changes of cropland across the Sichuan Basin of China and identified the relative importance of the main affecting factors. The results showed that topsoil pH (20 cm) has decreased by an average of 0.30 units (p < 0.001). Spatially, soil pH decline mainly occurred in the periphery of the Sichuan Basin where the initial pH (1980s) were less than 7.5. The magnitudes of soil pH decline were positively correlated with precipitation, base cation removal by crops and nitrogen fertilizer rates. Precipitation was identified as the most important factor in driving soil acidification. Moreover, the soil pH decrease was primarily buffered by soil carbonates and secondarily by soil CEC, and this study identified a critical level of 36.76 g kg−1 for soil carbonates, above which the acid-buffering capacity was mainly provided by soil carbonates, otherwise by soil CEC. These findings emphasize the importance of formulating precipitation-based optimizing agronomic management practices for preventing or mitigating cropland soil acidification, and also provide a regional observation-dependent evidence for the changing acid-buffering process during the soil acidification process.

Improving Selected Chemical Properties of a Paddy Soil in Sabah Amended with Calcium Silicate: A Laboratory Incubation Study

In Malaysia, the main constraints of rice yield and productivity are infertile soils and poor management practices because these soils are characterized by low pH, low nutrient availability, low organic matter, and high exchangeable Al and Fe ions, due to high rainfall and hot temperatures. Thus, an incubation study was conducted to determine the optimum amount of calcium silicate (HmbG brand) to improve the soil pH, electrical conductivity (EC), exchangeable Al, available P, and cation exchange capacity (CEC) of a paddy soil in Sabah, Malaysia. The Kelawat series (Typic Dystrudept) soil was incubated with calcium silicate at the application rates of 0 (T1), 1 (T2), 2 (T3), and 3 t ha−1 (T4) using a Completely Randomized Design (CRD) in triplicates for 30, 60, 90, and 120 days. The calcium silicate used significantly improved soil pH because of the release of SiO44− and Ca2+ ions, which neutralized and immobilized H+ ions. Furthermore, the neutralizing effects of the amendment impeded Al hydrolysis by up to 57.4% and this resulted in an increase in the available P in the soil by 31.26% to 50.64%. The increased availability of P in the soil was also due to the high affinity of SiO44− to desorb P from soil minerals and it is believed that SiO44− can temporarily adsorb exchangeable base cations such as K+, Ca2+, Mg2+, and Na+. Moreover, applying calcium silicate at 3 t ha−1 improved soil CEC by up to 54.84% compared to that of untreated soils (T1) because of increased pH and the number of negatively charged sites. The most suitable application rate of the calcium silicate was found to be 3 t ha−1 (T4). These findings suggest that calcium silicate can improve soil productivity and agronomic efficiency in rice farming. Greenhouse and field trials are necessary to ascertain the effects of the recommended treatments of this incubation study on soil productivity, rice growth, and yield.

Tree neighbourhood-scale variation in topsoil chemistry depends on species identity effects related to litter quality

Trees have a large impact on the topsoil chemistry and the strength and direction of this impact depend on the identity of the tree species. Tree species with nutrient-poor litter have the potential to degrade soil fertility, which is characterized by high acidity, low availability of essential nutrients for plant growth, and high levels of available Al and Fe. In contrast, species with more easily decomposing, nutrient-rich litter can ameliorate the soil quality. In this study, we are investigating the effects of tree species identity on topsoil chemistry on a small spatial scale. Our study site, situated in Białowieża Forest in Poland, replicates mature monocultures and two-species mixtures, using a pool of four tree species. Soil was sampled at a metre distance to the base of a tree and in the centre along a transect between two trees. We found that the total C concentration, plant available P and base cation concentration, and C/N ratio were all larger close to the tree. The pH was unaffected by the distance. We identified clear species identity effects on this distance effect. In particular, we found that the pH and base cations were affected more negatively by the proximity to a tree nearby nutrient-poor trees in comparison with nutrient-rich trees. However, no non-additive diversity effects in mixtures could be distinguished. Our results highlight the ameliorating effects of admixing nutrient-rich species with nutrient-poor species and the importance of tree species choice in regard to the topsoil chemical composition on a small within-stand scale.

Soil Organic Matter Fractions in Relation to Root Characteristics of Different Tree Species in Altitude Gradient of Temperate Forest in Carpathian Mountains

The roots are a key functional component of belowground systems and one of the main factors influencing the quality and quantity of soil organic matter. Our research aimed to determine the fractional composition of the soil organic matter (SOM) in soils under various tree species on an altitude gradient. In our research, we related the SOM fractions with the root characteristics. There is a lack of information on the relationship between the SOM fractions and the root properties. We assessed labile and heavy fractions of SOM content in forest mountain soils with a climosequence approach. The study plots were established at 600, 800, and 1000 m above sea level in a beech stand (Fagus sylvatica L.) and a fir stand (Abies alba Mill.). In this case, three research plots with beech and fir were designated in each altitude variant. Forest stands growing in the same soil conditions were selected for the study. The research used stands of similar age with the same tree canopy density. The basic physicochemical properties (pH, hydrolytic acidity, carbon and nitrogen content, base cations content) and the fractional composition of the SOM were determined from soil samples. In addition, we determined the basic characteristics of the roots (diameter, length, biomass, decomposition, production). The correlation between soil organic matter fractions and root characteristics was recorded. This study confirmed the importance of climatic conditions in shaping the fractional composition of forest soils. In the highest locations, characterized by lower temperatures, the light fraction of the SOM exhibited the highest C and N content, which is the effect of slower decomposition processes. Apart from climatic conditions, the stabilization of SOM is influenced by the tree species composition of a forest stand. Beech forest stands lead to a larger accumulation of a heavy fraction of SOM. This study indicates a positive correlation between the light fraction of SOM, root biomass, and decomposition rate of roots. Our research shows that avoiding single-species coniferous stands and introducing admixtures of deciduous species, which increase the heavy SOM fraction, is justified in forest management.

Traditional human practices protect diversity of open forests threatened by ticking nutrient time bomb

Open forests are among the world's most species-rich ecosystems but these are now suffering from strong environmental pressure. With the increasing frequency of drought events accompanying climate change, open forests are now at high risk of canopy openness, an associated increase in nutrient load, and a consequent reordering of the plant community. Based on an 11-year field manipulative experiment, we examined whether the reintroduction of traditional forest uses, in particular the regular removal of litter which has been practiced for many centuries in Europe, may mitigate eutrophication and protect the ancient plant diversity of open forests. We examined vascular plant composition in 64, 3 × 3 m plots in 32 randomized blocks, each consisted of one litter-removal and one control plot in a subcontinental thermophilous oak forest dominated by Quercus petraea (Czech Republic, Central Europe). We analyzed how regular litter removal influenced the changes in topsoil nutrients and diversity and abundances of perennial, short-lived monocarpic and open oak forest plant species after eleven years of the annual application of this management. The regular litter removal significantly mitigated eutrophication by a reducing total nitrogen, and significantly decreased the amounts of base cations Ca2+ and Mg2+ in the topsoil. The studied plant species groups responded differently. Perennial and open oak forest species significantly increased their richness and abundances in the litter-removal plots and at the same time their diversity did not change significantly depending on inter-annual weather conditions. In contrast, litter removal negatively affected abundances of short-lived monocarpic species, whose richness was also considerably influenced by weather conditions (decreased the most in years with spring droughts). Moreover, we have found a protective effect of regular litter removal on drought-sensitive open oak forest species that survived in the litter-removal plots, whereas some completely disappeared from control sites during the period of repeated drought events. Our study thus demonstrates that litter removal is a tool with high potential in maintaining biodiversity in open forests affected by climate change.

Evaluating acid-aluminum stress in streams of the Northeastern U.S. at watershed, fish community and physiological scales

In spite of overall improvements in air and water quality, biological stress from low pH and high concentrations of inorganic aluminum continue to impact fish and fish habitat in northeastern North America, with independent and interactive effects on individuals, populations and communities. Integrative indicators can therefore be useful in monitoring both impact and recovery across multiple scales. Using coupled water chemistry (pH, conductivity, and base cation and inorganic aluminum concentration), geographic (site elevation and watershed area) and biological (fish diversity, fish abundance, gill aluminum concentration and gill physiology) data, we developed an integrated indicator of acid-aluminum stress across the White and Green mountains in central New England, USA. As has been established in a number of previous studies, preliminary analysis clearly indicated that across all sites, inorganic aluminum concentration was consistently greatest during the spring season. Structural Equation modeling (SEM) revealed that toxic conditions (concurrent low pH and high concentrations of inorganic aluminum) were well summarized with an integrated toxicity score, related to both base cation concentrations and elevation, with sites at higher elevations more likely to experience toxic conditions as well as low base cation concentrations. Fish diversity and abundance generally trended negatively with toxicity score, with fewer cyprinids and sculpins at high toxicity score sites. In spite of considerable variation among individuals, gill aluminum was positively related to toxicity score for both Atlantic salmon and brook trout. Observed elevated gill aluminum levels associated with reduced gill metabolic activity in Atlantic salmon smolts from impacted systems likely result in impaired osmoregulatory function and seawater tolerance. Overall, our results suggest that the integrated toxicity score metric is associated with a syndrome of acute physiological stress, reduced abundance, and low species diversity for sensitive stream fishes in New England, and can likely serve as a reliable indicator of continued impairment or recovery of acid-aluminum vulnerable systems in this ecoregion.

Fine root biomass of European beech trees in different soil layers show different responses to season, climate, and soil nutrients

Fine roots are crucial for water and nutrient acquisition in plants; yet it is unknown how nutrient inputs and soil fertility in forests influence fine root biomass seasonal trajectories. Here, we hypothesized that standing fine root biomass increases with addition of a limited resource and shows different seasonal patterns depending on nutrient availability and phenology. We further hypothesized that the influence of climate is greater in the organic layer, causing larger responses of root biomass to climate in the organic layer and stronger responses to nutrient changes in mineral soil. We conducted our study in three European beech (Fagus sylvatica) forests representing a soil fertility gradient with high, medium, and low phosphorus (P) contents. A fully factorial fertilization regime with N and P was applied at each forest site. To test our hypotheses, we conducted soil coring in spring and fall for 2.5 years. Soil cores were fractionated into organic layer (Oe + Oa layer) and mineral soil (A horizon) and used to determine fine root biomass, soil pH and moisture, total concentrations of soil and root nutrients (basic cations, micronutrients, S, P, N, C), soluble concentrations of soil and root P. Fine root biomass in the mineral soil at the forest site with the lowest soil P content increased in response to P addition. Pheno-seasonal changes caused increases in soil P and N in spring and opposing cycling of biomass and fine root labile P contents at the P-medium and P-high sites. Contrary to our expectation, we observed stronger climatic effects on fine root biomass in the mineral soil, whereas soil moisture was more important in explaining fine root biomass variation in the organic layer. Our results show that seasonal patterns of fine root biomass are dependent on the stratification of environmental factors with soil depth and imply negative consequences for fine root biomass in the organic soil layer due to acute soil water content fluctuations and climate change effects in the mineral horizon due to long-term precipitation changes.

Impact of crop production and eucalyptus forestry on a Ferralsol under native grassland in southern Brazil

The extreme south of Brazil is marked by a moist subtropical climate, where land use has changed widely from traditional grazing to intensive agriculture and plantation forestry, and in most cases the effects on soil properties are poorly known. Here, we assessed how conversion from Pampa native grasslands biome to annual crops and eucalyptus stands changed physical, chemical and mineralogical properties of a Dystric Rhodic Ferralsol (kaolinitic) after 30 yrs. (1988–2018). The soil was analyzed by chemical extractions, X-ray diffraction, X-ray fluorescence, diffuse reflectance, magnetic susceptibility, and petrographic microscopy. Soil organic carbon concentrations in the top 5 cm under eucalyptus was more than twice as high as under native grasslands, with no significant differences beneath that layer, or under annual crops. Basic cations and available P increased under croplands as an effect of liming and fertilization, but unexpectedly also under non-fertilized eucalyptus, which was probably due to biogeochemical cycling from deeper layers. Significant decreases in magnetic susceptibility, total Fe and Al (determined by X-ray fluorescence), and dithionite-extractable Fe in the soils under eucalyptus and cropland could be ascribed to lower clay contents compared to those of the native grasslands. Such changes were also evidenced by X-ray diffraction through the decrease in peak areas of hematite and kaolinite, the latter probably decreasing its crystallinity whereas an interstratified 1:1–2:1 phase was more stable. Soil microstructure was massive, i.e. dense and with few fissure pores under native grassland, but under croplands and especially eucalyptus was much looser and contained more excrements and faunal features. Our data helps understand how land use change in this poorly studied biome affects differently key soil properties involved in agriculture and ecosystems, especially SOC and chemical composition.

Determination of Cation Exchange Capacity of Calcareous Soils: Comparison of Summation Method and Direct Replacement Method

ABSTRACT The purpose of this study was to compare cation exchange capacity (CEC) values obtained by direct measurement and by summing the exchangeable base cations (EBCs) in calcareous soils. The seven soils used in this study were collected in Nassau, Bahamas, and in south Florida. The collected soils were analyzed for pH, organic matter, calcium carbonate, CEC, and EBCs. The CEC was determined using Bower’s method with slight modification, which featured 1 M sodium acetate at pH 8.2 as saturating solution, 70% ethanol for washing, and 1 M ammonium acetate at pH 8.2 for extracting adsorbed sodium ions. The extracted sodium ions were quantified using an inductively coupled plasma-optical emission spectrometer (ICP-OES). The exchangeable base cations were extracted using 1 M ammonium acetate solution at pH 8.2 and quantified by ICP-OES. The cation exchange capacity values determined by the direct method and summation method were comparable for all the soils used in this study. Summation CEC was not significantly different from the measured CEC (p < 0.05) for all the soils. These results imply that the summation method based on EBCs extraction with 1 M ammonium acetate at pH 8.2 may be a viable choice for soil testing laboratories to accurately estimate CEC in calcareous soils.

Diverse structures and multi-step dielectric relaxation of three lead bromide hybrid crystals based on 1-aminopyridinium and its cyano-substituted Schiff bases

Oriented design of crystal structures to obtain specific properties is one of the hot topics in the field of chemistry and materials. In this paper, three organic–inorganic hybrid crystals were synthesized by the reaction of 1-aminopyridinium salts with o-, m-, and p-cyanobenzaldehyde and PbBr2. The asymmetric unit of 1 ([1- aminopyridinium][Pb2Br5], P21/m) contains half of the 1-aminopyridinium cation and the anion forms a zig-zag shaped puckered sheet of [Pb2Br5]∞; while 2 ([m-cyanobenzaldehyde-1-aminopyridinium][PbBr3], Pna21) includes a m-cyanobenzaldehyde-1-aminopyridinium Schiff base cation, and the anion forms a [PbBr3]∞ single chain. On the other hand, 3 ([p-cyanobenzaldehyde-1- aminopyridinium][PbBr3], P21/c) consists of a p-cyanobenzaldehyde-1- aminopyridinium Schiff base cation, with the anion forming a [Pb2Br6]∞ double chain. Structural analysis and energy framework calculations show that 2 possesses stronger π-π stacking and hydrogen bonding interactions, and its lattice energy and thermal stability are higher than those of 1 and 3. The combined use of CE and dielectric modulus analysis reveals a good correlation between multi-step dielectric relaxation and intermolecular forces. This strategy of modulating the crystal structure and dielectric properties by altering the position of the substituents provides useful assistance in the design of new relaxation dielectric materials.

Analysis of Long-Term Effect of Tillage Systems and Pre-Crop on Physicochemical Properties and Chemical Composition of Soil

The aim of the present study was to analyse the physicochemical properties and chemical composition of soil after years of applying varied tillage systems and pre-crops. The field experiments were carried out in Lipnik in Poland. The experiment was conducted over 25 years, with factor I–3 tillage systems: ploughing (A), ploughless (B) and direct sowing (C), factor II-pre-crop–1–faba bean, 2–sugar beet. Simplified tillage systems were used, and increased acidity was found in both layers due to lower pH, as well as an increase in exchangeable aluminum, hydrolytic acidity and exchangeable acidity of soil. The simplification of tillage system resulted in no significant effect on the following soil parameters: sum of base cations (TEB), cation exchange capacity (CEC) and electrical conductivity (EC). In both layers, there was a marked increase in the content of total nitrogen, carbon and available magnesium in soil with ploughless (B) and direct sowing (C) tillage systems. The change of the tillage system, which implied tillage reduction, was found to be the factor which has a significant effect on the physicochemical properties and chemical composition of soil. Tillage resulted a greater effect on the physicochemical properties, whereas pre-crop was found to affect the changes in chemical composition of soil to a greater extent. The results obtained in the research indicate that the tillage systems ploughless (B) and direct sowing (C) can be applied in practice.

Use of major ions to evaluate groundwater chemistry and identify hydrochemical processes in a shallow coastal aquifer in southeast Brazil

Coastal aquifers of southeastern Brazil have a fundamental role in economic and social terms, as it is a densely populated region with intense economic activity. The present research was carried out in the coastal region of the State of Rio de Janeiro and enclosed the Brazilian Nuclear Power Plants (NPP) site. The study aimed to assess the hydrochemistry of the shallow aquifer at the NPP's site and surroundings. The hydrochemical study was carried out based on data from 12 water samples, collected in October 2018, in which parameters were measured in situ (such as electrical conductivity, total dissolved solids, temperature, and pH) and in the laboratory (such as alkalinity; Ca2+, Mg2+, Na+, K+; Cl−, SO42−, and silicon). Using Piper and Chadha diagrams, the research identified four water types: Group 1 (Ca2+–Na+–HCO3−), Group 2 (Ca2+–HCO3−), Group 3 [Ca2+ (Na+ rich)–HCO3−], and Group 4 (Na+–Cl−). From the hillsides towards the beach line, the research results suggest a hydrochemical evolution of local groundwater from Group 1 (high rainwater influence), passing through Group 3 (intermediate between Group 1 and 2) and Group 2 (rock influence), to Group 4 (seawater like). The waters of groups 1 to 3 showed potential for base cation exchange (softening or freshening process), while, in Group 4, the potential is for reverse cation exchange (hardening or salinizing process). In a general hydrogeology context, the methods and applied techniques proved to be particularly efficient in identifying potential hydrochemical processes. Noteworthy is the freshening cation exchange identified in the shallow aquifer at NPP’s site. Therefore, theoretically, in case of an accidental release of radionuclides from the NPP to the aqueous phase, the local clay lenses can capture the divalent cation Ra2+ in a natural contamination attenuation process.

Evaluation of simple and multivariate linear regression models for exchangeable base cation conversion between seven measurement techniques on South African soils

Conversions of exchangeable base cation concentrations between different analytical methods are required for comparisons of soil test results with norm values developed using specific methods. Different methods vary in extraction efficiency due to underlying chemical mechanisms of cation exchange. There is a lack of knowledge pertaining to the combined effects of soil physicochemical properties on the accuracy and parsimony of conversion models. Thus, the aim of this study was to develop equations for conversion of exchangeable base cation (Ca, Mg, K and Na) concentrations between seven different methods of measurement for soils dominated by moderate-activity clays. Additional objectives included the discussion of chemical mechanisms influencing nutrient extraction efficiency, development of root mean square error (RMSE) thresholds for model selection, and evaluation of the effects of soil physicochemical properties on model performance. The ammonium acetate (1 M and 0.2 M, pH = 7), compulsive exchange, Ambic-I, Mehlich-III, Bray-II and Citric acid (1%) soil test methods were performed on 57 soils from a Mediterranean climatic zone. Simple linear regressions (SLR) as well as multivariate linear regressions (MLR) incorporating soil physicochemical properties as parameters were developed. The accuracy of cross-validated models was comparable to accuracy of predictions for samples included in calibration. MLR equations (RMSECV = 1.4–1.6 cmolc kg−1, 0.4 cmolc kg−1, 16–20 mg kg−1 and 25–40 mg kg−1 for Ca, Mg, Na and K, respectively) were generally more accurate than SLR models. Relationships between Ca content extracted by different methods depended on soil alkalinity. Use of the developed SLR or MLR models to convert nutrient quantities between different methods should be chosen based on contextual accuracy requirements.

Soils developed on the Si-poor, alkali-rich pyroclastic rocks of the Colli Albani volcanic district (Central Italy): The effect of leucite, clinopyroxene and phlogopite on the base cations mobility

The Colli Albani volcanic district emplaced huge pyroclastic-flow deposits up to 20 m thick in the southeastern suburbs of the City of Rome. The soil quality onto the gentle slopes of the Colli Albani has certainly contribute to the growth of Ancient Rome, a city with one million inhabitants as early as 2000 years ago. Interestingly, the Colli Albani soils developed on K-foiditic pyroclastic rocks with peculiar low silica, high alkali and high CaO composition. In the past, the productivity of the Colli Albani soils was maximized without the understanding of the unique physical, chemical, and mineralogical properties of these soils; now an in-depth knowledge of the Colli Albani soils is necessary to respond to the current and increasingly demand of sustainable soil use. Textural, mineralogical and chemical data indicate that the evolutionary stages of soil development are bedrock →leucite (Lct)-bearing soils→quartz (Qz)-bearing soils. The bedrock is made up mainly of leucite, clinopyroxene, phlogopite, zeolites and K-foiditic glass that is turned in an amorphous phase characterized by the Al-rich, cations base-poor and hydrated composition (i.e. halloysite-like chemistry). This reaction occurs in the syndepositional conditions (i.e. temperature up to ∼600 °C) and causes the absence of glass and the abundant crystallization of halloysite in the Colli Albani soils. The Lct-bearing soils are organic matter-poor, weakly weathered volcanic matter, comparable to the vitric andosols, showing incipient halloysite crystallization. As the degree of weathering increases, i) grain size decrease, ii) pH remain neutral, iii) highly soluble leucite, analcime and other zeolites, are rapidly dissolved, iv) alkali, Ca and Mg are leached, v) silica, Al and Fe activities increase and vi) halloysite stability field enlarges. The resulting Qz-bearing soils are made up mainly of halloysite, quartz, oxy-phlogopite and calcic clinopyroxene showing a lower cation exchange capacity (CEC) compared to the Lct-bearing soils. However, in Qz-bearing soils the CEC it is rarely <20 cmol (+)kg−1 because KEx, MgEx and CaEx are released from the oxy-phlogopite and the strongly weathered clinopyroxenes characterized by the “gothic” texture.