Study on hydrophysical and chemical parameters of Polish and Slovak soils modified with zeolitic additives

Application of soil modifiers is a widely used practice in agriculture to improve soil quality in support of good agricultural practices. This paper presents an assessment of the effect of zeolite modifiers combined with four soils of Polish and Slovakian origin on their hydrophysical properties. Under laboratory conditions, the characterization of the applied soil additives was carried out along with particle soil analysis. In addition, the prepared soil mixtures were examined using contact angle and saturated hydraulic conductivity. The results suggest that the increase in hydrophobicity occurred mainly after the application of fly ash, and the values for Polish Silty clay soil and Slovak soils: Sandy soil, Silt loam soil, and Silty clay soil compared to the control changed from 73.02° to 96.22°; 8.67° to 24.88°; 29.23° to 33.94° and 19.9° to 26.16° respectively. The increase in hydrophobicity could be explained by the higher CaO content of the high-carbon fly ash compared to the other materials. The parameters of saturated hydraulic conductivity were reduced after the application of all zeolite materials in the case of Polish Silty clay and Slovak Sandy soils. By filling the space between the soil particles, the porous soil additives decreased the hydraulic conductivity. In Slovak soils such as Silty loam soil and Silty clay soil, the opposite effect was observed. The soil additives increased the number and size of pores, which resulted in faster filtration of water and thus an increase in the saturated hydraulic conductivity value.


Introduction
Soil is a fundamental element of the environment, being a three-phase system made up of a solid phase, a liquid phase and a gaseous phase.The particles that belong to the solid phase account for about half of the soil volume, the rest being the pores in between them.The geometry, size and connections of the soil particles in its structure create a porous system with unique hydraulic properties.These properties are very important for proper crop production.In agriculture, many well-known soil additives are used to soil improvement (Rousseva et al., 2017).There are zeolites among them, both natural and synthetic ones.They are crystalline, porous aluminosilicates most often of sodium and calcium (Inglezakis and Zorpas, 2012), which can be applied as a component of complex fertilizers.According to Soudejani et al. (2019), the addition of zeolites to the composting of organic solid waste allows the production of a material that leads to higher water retention in the soil, reduces nutrient loss, and improves crop quality.A characteristic property of zeolites is their ability to retain water and nutrients.They are also able to remove water from the tubules (so-called "zeolite water") without destroying their structure (Ghorbani et al., 2022).In this way, zeolites improve infiltration rates and saturated hydraulic conductivity.In addition, they affect cation exchange capacity and prevent water loss from deep percolation (Talebnezha and Sepaskhah, 2013;Chmielewska, 2014;Mondal et al., 2021).Belviso et al. (2022) confirmed that the obtained effects depend on the dose of applied zeolite material.With the increase in the amount of zeolite added to the soil, the range of available water for plants decreased, making the soil less suitable for plant growth (Belviso et al., 2022).Another substance that can be able to absorb a large amount of water (up to 80%) and reduce infiltration (2-16%) is fly ash.The hydraulic properties of this material depend on the density and depth of the studied layer and also the specific chemical composition of fly ash.Specific chemical composition of fly ash is responsible for their different hydraulic properties.Calcium fly ashes (Class C fly ashes according to ASTM C618, 2015) are characterized by significantly lower hydraulic conductivity compared to silicon fly ashes (Class F fly ashes according to ASTM C618).However, mixtures of fly ashes of class F with lime and calcium bentonite may contain some amount of CaO, which significantly affects the hydraulic properties of the material (Zabielska-Adamska, 2020;Porbaha et al., 2000).Most of the available scientific papers are focused on natural zeolites.Therefore, in this research, synthetic zeolitic materials, which are produced from energy waste (fly ash), were proposed as soil additives.The main aim of the experiments was to determine hydrophysical and chemical properties of morphologically different soils collected in Poland and Slovakia modified with three types of zeolitic materials.

Experimental design
For the experiment, four soils with different land use were selected from regions in Poland and Slovakia.One soil from Poland, Polish Silty clay soil, was collected from Lubelskie Voivodeship area (Jabłonna, eastern part of Poland, 51°05'N, 22°36'E, long-term abandoned field).Three soils were taken from regions of Slovakia: first, Slovak Sandy soil, was taken from the site of Záhorská nížina (Plavecký Štvrtok, western part of Slovakia, 48°37'N, 16°99'E, long-term abandoned field), the second soil, Slovak Silt loam soil, was collected from the Nitrianská pahorkatina site (Dolná Malanta, central western part of Slovakia, 48°31'N, 18°14'E, agriculturally used country) and the third, Slovak Silty clay soil, was taken from the Východoslovenská nížina site (Senné, eastern part of Slovakia, 48°66'N, 22°02'E, grassland).Disturbed samples were collected from the top 20 cm of the soil profile at all areas.The natural dry bulk density of all soil types was determined based on undisturbed samples.Disturbed samples were air dried and sieved to a fraction with a particle size ≤ 2 mm in laboratory conditions.The bulk density of all pure soil types (Control) were prepared to be the same as natural bulk density (Table 1).Mixtures of soil and zeolitic materials were prepared by mixing one type of soil with one selected material at 1% dose (per weight) in laboratory conditions.Each treatment (soil and zeolite mixture, also Control) was prepared in three replicates in steel cylinders with a volume of 100 cm 3 .Soil mixtures with zeolite materials were compared with control samples, i.e., soils without additives.

Soil characterization
The main properties of the soils were investigated by conventional methods i.e. the pH values were measured electrochemically in H2O using a digital pH-meter (Radiometer Copenhagen).The ash content (A) was calculated by weighing the residue after 5 h of combustion at 550°C in a muffle furnace (FCF 12 SP,Czylok).The total variable surface charge (Qtot) was established by potentiometric titration with Titrino 702 SM (Metrohm) (Józefaciuk, 2002).

Soil textural analysis
The hydrometer method was used for soils particle size distribution analysis.The principle of this method is based on Stokes' equation (Eq.1):

The measurement of decreasing densities of suspension
as a function of time, due to soil-particle sedimentation.This method was described in detail by Klute (1986).
Based on textural fractions of sand, silt and clay were all soils classified according to USDA classification.

Zeolite characterization
For the study, three materials provided by the Lublin University of Technology were used in the experiments.
One of them was high-carbon fly ash (HiC FA), a waste material produced as a result of conventional coal combustion.This product was applied as a substrate for the synthesis of the subsequent materials, i.e., Na-P1(C) carbon-zeolite composite and pure Na-P1 zeolite with no ash residue in its structure.The exact procedure for synthesizing the materials was described by Panek et. al. (2021).
The morphology of the high-carbon fly ash (HiC FA), zeolite (Na-P1) and carbon-zeolite composite (NaP1(C)) was analyzed by Scanning Electron Microscopy (Phenom ProX, Thermo Fisher Instruments, Somerset, NJ, USA).The BSD detector was used, and the accelerating voltage was 10 kV.To achieve high quality images, all samples were coated with a layer of gold using a sputter coater (CCU-010 LV, Safematic GmbH, Zizers, Switzerland).Textural parameters of zeolitic materials were determined by nitrogen adsorption/desorption method (ASAP 2420 analyzer, Micromeritics Inc.).Specific surface area (SBET), total pore volume (Vt), micro pore volume (Vmic), and average pore diameter (D) were estimated.Specific surface area was calculated using the BET equation (Brunauer et al., 1938), (Eq.2): The elemental composition of the samples was determined by semi-quantitative energy-dispersive X-ray fluorescence on an Epsilon 3 spectrometer (Panalytical, Eindhoven, the Netherlands).The equipment consisted of a Rh 9 W, 50 kV, 1 mA X-ray lamp, a 4096-channel spectrum analyzer and a high-resolution solid-state SDD detector cooled by a Peltier cell.The results obtained included LOI.

Analysis of contact angle
Measurements of the contact angle of Polish and Slovak soils with and without amendments were performed using goniometer Drop Shape Analysis System (DSA100, Krüss, Germany).The sessile water drop method was used to determine differences in the wettability of the samples.Following the methodology, a drop of water was applied to the surface of the sample using a goniometer syringe, and afterward, the contact angle of the water drop was measured.When α≥90°, the liquid doesn't wet the studied material and it is considered as hydrophobic.

Analysis of saturated hydraulic conductivity
Saturated hydraulic conductivity (K) was determined by pure soils and prepared mixtures of each soil type and zeolitic materials in steel cylinders.We used a modified falling-head (variable) method to measure the amount of water that goes through the soil/mixture sample in a fixed time interval (modified by Novák and Hlaváčiková, 2019).The water level above the soil/mixture sample decreases over time (Fig. 1).The same method of measurement was used for all soil types to avoid errors with different methodological processes.All values of K measurement were calculated for cm per day unit, for better visualization in all treatments.

Results and discussion
The results of untreated soils' hydrophysical and chemical properties are summarized in Nevertheless, all types of soil demonstrated a contact angle below 90°, which indicated their hydrophilic nature.
Textural parameters of zeolitic materials are presented in Table 3.Based on the results, it can be concluded that the SBET surface of the selected materials is poorly developed.Na-P1 had the smallest SBET parameter (69.85 m 2 g -1 ), while it contained larger pores (D = 6.93 nm) than HiC FA (D = 5.66 nm).Accordingly, the zeolitization process strongly affected the textural properties by increasing the average pore diameter, as well as reducing their total pore volume.
Representative SEM micrographs of the applied soil conditioners are shown in Fig. 2. The analysis of the fly ash sample (Fig. 2A) indicates the presence of irregular forms of quartz, spherical structures of aluminosilicate glaze, and also unburned carbon fragments.Carbon sinters with embedded beads of aluminosilicate glaze are also visible.Pure zeolite Na-P1 (Fig. 2B) has no residual fly ash in its structure.It forms spherical, highly regular zeolite crystals.Na-P1(C), presented in Fig. 2C, creates very well-formed crystals, forming single clusters or

Saturated hydraulic conductivity
Saturated hydraulic conductivity (K) varied with the addition of zeolitic materials (Fig. 4).The dependen ce of K on soil texture has been well documented and values of K depend on the size distribution of soil particles, i.e. soil texture, and the spatial distribution of these particles, i.e. soil structure.Polish Silty clay soil, Slovak Silty loam, and Silty clay soils exhibited low value of the K.It was correlated with silt and clay content.These types of particles are small and have small pore  In Polish Silty clay soil (Fig. 4A), there was a negative effect of zeolitic materials, when the K value decreased by half after the addition of additives in comparison to control.In Slovak Sandy soil (Fig. 4B), the observed effect was positive.The effect of the zeolite additives caused the K values to decrease by about 30-38% compared to the control.This is may be a positive finding, because the infiltration is very quick in Slovak Sandy soil and it is necessary to slow it down.In Silt loam soil (Fig. 4C) only the effect of zeolite (Na-P1) on K values was found.This effect was negative because, it is not needed to reduce the K parameter in this type of soil.The changes in K values with the other two additives were not significant in comparison to control.In Slovak Silty clay soil were found also positive changes in K values after zeolite additieves in comparison to the control (Fig. 4D).There is needed to increase the infiltration in this type of soil.The highest increase was observed with zeolitic composite (Na-P1(C)), which was more than 600%.
As mentioned in the case of contact angle results, the chemical composition of zeolite materials may affect hydraulic conductivity.As the micropore area and porosity of the additives used increases, the hydraulic conductivity decreased, as can be seen in Polish Silty clay soil and also in Slovak Sandy soil.This was due to the fact that the additive particles filled the space between the soil particles and as a result, the water was filtered lower than unmodified soil (Bilardi et al., 2020).Also other authors observed impact of soil amendments (biochar) on K values in different soil (Toková et al., 2023;Vitková et al., 2019;Brockhoff et al., 2010;Uzoma et al., 2011).In the case of Slovak Silty clay soil, the opposite effect was observed.This could be due to the fact that the additives increased the number and size of the pores.Therefore, the water was filtered faster and the K values increased.

Conclusion
It can be concluded that the saturated hydraulic conductivity strongly correlates with specific soil properties.The addition of various zeolitic materials had a negative impact on Polish Silty clay soil.Nevertheless, in the case of Slovak sandy soil, a positive effect was obtained due to the slowing down of infiltration, which is preferable for this type of soil.However, it is not possible to select one addition that would show the best results in these soils: the zeolite (Na-P1) had the best effects in the Slovak Sandy soil, it was the zeolitic composite (Na-P1(C)) in the Slovak Silty clay and in the Polish Silty clay soil had all additions similar effects.There was even observed a negative effect of zeolite (Na-P1) in Slovak Silt loam soil; the other two zeolitic additions did not bring significant changes.
The results of the contact angle also clearly indicate that the type of soil being used determines certain values, which were obtained in these experiments.Nevertheless, the application of an addition such as fly ash caused the hydrophobicity of all studied materials to increase.The wettability of modified soils depended largely on the base material which is soil without the additive.As an example, the contact angle for Slovak Sandy soil after the addition of 1% Na-P1(C) and Na-P1 rapidly decreased.Sandy soils with a coarse-grained structure are considered to be less hydrophobic than silty soils, which is attributed to their more permeable structure.In this case, the addition of Na-P1(C) and Na-P1 caused an increase in loosening of the soil structure and consequently a decrease of the contact angle.
weight of nitrogen adsorbed at a given relative pressure (p/p 0); xmthe monolayer capacity, which is the volume of gas adsorbed at standard temperature and pressure (STP); Cthe constant.
Fig. 3. Representative images of contact angle measurements for Polish Silty clay soil and Slovak soils: Sandy soil, Silt loam soil and Silty clay soil.Images shows control samples with soil without additives and soil mixtures with zeolite materials Na-P1(C), Na-P1 and HiC FA.
a result of which the water does not filter quickly.Furthermore, Slovak Sandy soil showed the largest value of K.This type of soil dominated by large sand particles tend to have relatively large pore spaces and thus large values of K.

Table 1 . Natural and prepared dry bulk density of all studied treatments and standard deviations Treatment Natural dry bulk density [g cm -3 ] Prepared dry bulk density [g cm -3 ]
Table2and they revealed differences of the soils.Polish Silty clay, Slovak Silty clay, and Slovak Silt loam soils belonged to neutral, silty soils with low sand content (Polish Silty clay -6%, Slovak Silty clay -11%, and Slovak Silt loam -15%) whereas Slovak Sandy soil was slightly acidic soil with high sand content (91%).The Slovak Silty clay soil had the highest pH parameter (7.4), specific surface area (44.7 m 2 g -1 ) and total variable surface charge value (16.6 cmol kg -1 ) compared to the other tested soils.On the other hand, this soil had the lowest ash content (87.9%).Sandy soil, due to the highest sand content in its structure, had the lowest value of contact angle (8.7°).