In Slovakia, maize silage is preferred as the input material for biogas production whereas it should be used primarily as feed for cattle. The purpose of this paper is to point out the possibilities of using the fast-growing giant reed Arundo donax L. that is not used as fodder and can be grown on low-quality agricultural land. The experimental stand of A. donax L. used in the study provided a yield of 60.8 t ha-1 of fresh biomass in the third year of cultivation. Part of the biomass produced was ensiled as maize and later the silage was co-fermented with cattle excrements and pig slurry. The resulting biogas can be used as fuel for internal combustion engines. The average content of CH4 and CO2 is 52% and 44%, respectively. These values are very similar to the composition of maize silage biogas. The average hydrogen sulphide content in the biogas from A. donax L. was 730 ppm. The disadvantage is that the biogas production is 46% lower compared to maize silage.

Bioenergy is considered the largest contributor to the renewable and sustainable energy sector worldwide, playing a significant role in various energy sectors such as heating, electricity supply, and even in replacing fossil fuels in the transportation sector. As part of renewable, low-carbon energy systems, bioenergy can also ensure atmospheric carbon sequestration, provide numerous environmental and socio-economic benefits, and thus contribute to achieving global climate change goals, as well as broader environmental, social, economic, and sustainable development objectives. The use of bioenergy can significantly reduce our carbon footprint and thus contribute to improving the environment. While bioenergy conversion of biomass produces some amount of carbon dioxide, similar to traditional fossil fuels, its impact can be minimized by replacing forest biomass with fast-growing trees and energy crops. Therefore, fast-growing trees and energy crops are the primary raw materials for bioenergy. The results of the research in this publication confirm the high efficiency of biomass depolymerization through thermochemical conversion. The principle of continuous biomass conversion was used at a process temperature of 520 °C. The experiments were carried out in the Biomass Gasification Laboratory at the AgroBioTech Research Center of the Slovak University of Agriculture in Nitra. The biomass used for the experiments was from energy-producing fast-growing willows, specifically the varieties Sven, Inger, and Express. The aim was to determine the amount of biochar produced from each of these tree species and subsequently to investigate its potential use for energy purposes. During the experiments, 0.106 kg of biochar was produced from 1 kg of Inger willow biomass, 0.252 kg from 1 kg of Express willow biomass, and 0.256 kg from 1 kg of Sven willow biomass. A subsequent goal was to determine the production of gas, which can also be used for energy purposes. The biofuel samples obtained were subsequently subjected to thermogravimetric analysis to determine moisture content, volatile matter, and ash content. The ash content in dry matter ranged from 6% to 7.28%, while the volatile matter in dry matter was between 92.72% and 94%. The moisture content in the samples ranged from 1.7% to 2.43%. These results may contribute to innovative insights into biomass depolymerization and help define optimized parameters for thermochemical conversion, as well as the required biomass composition, with the goal of generating second-generation biofuels in the most cost-effective way.

Plantations of fast-growing crops represent local agroecosystems providing provisioning services in the form of phytomass that can be utilized for energy and/or non-energy purposes. Permanent grasses such as Miscanthus are identified as potentially suitable sources of raw materials for the output of second-generation biofuels. The experiments focused on the production ability of the perennial energy grass Miscanthus were performed in the region of SW Slovakia. It was confirmed that the studied genotypes (Miscanthus sinensis Tatai and Miscanthus × giganteus) exceeded the cost-efficient level of biomass production. The above-ground biomass of the studied genotypes was ensiled and afterwards fed to the experimental fermenters to evaluate the biogas production. The experiments with individual silage mixtures lasted 600 hours. The total amount of biogas produced from M. × giganteus and M. sinensis Tatai silage mixture was 273 dm3 and 328 dm3, respectively. The average share of methane in the biogas of both studied samples of silage mixtures was 51%. On the basis of the 10-year average yields of the studied Miscanthus genotypes achieved in our conditions, it is possible to produce 8 181 m3/ha (M. × giganteus) and 11 248 m3/ha (M. sinensis Tatai) of biogas from the silage mixtures. The achieved production represents sufficient and stable amount of biogas and its use can be economically efficient and sustainable in the long run in SW Slovakia.

When cultivating a selected field crop (alfalfa), we aimed to examine its positive effects on the variability of soil infiltration capacity. A total of 21 monitoring points were proposed for investigating soil hydraulic conductivity on the targeted plot with a total area of 47.64 ha, divided between the irrigated and non-irrigated areas. The plot is located outside the village of Oponice (Slovak Republic) and is managed by VPP Kolíňany. The study of hydraulic conductivity has been ongoing on the selected plot for several years. The presented results come from a two-year experiment, during which work operations related to the cultivation of alfalfa were carried out on the plot. The unsaturated hydraulic conductivity of the soil was assessed several times a year using a Mini Disk Infiltrometer, while soil moisture at monitoring points and the dependence of the measurement date (work operations, weather conditions) were also monitored. The average soil moisture content in the pilot measurements reached 18.77% vol. (CV = 1.44%), in the secondary measurements 17.21% vol. (CV 20.49%), in tertiary measurements 15.27% vol. (CV = 10.38%), and in the last measurements 15.26% vol. (CV = 10%), which ultimately represents a positive result of soil moisture balance. To test the significance of the differences between measurements taken across the entire surveyed plot, a one-factor ANOVA analysis was used to compare the measurement dates. The results showed a statistically significant difference when examining the effect of the time period of soil infiltration capacity monitoring between all measurements (p = 0.004). The mutual combinations of individual measurement dates were mostly significant (p = 0.03 for IDM1, IDM2; p = 0.003 for IDM2, IDM3), except for one case without a significant difference (IDM3, IDM4; p = 0.52). The second hypothesis was confirmed only at some monitoring points, and it can be stated that the irrigated area had a more significant effect on the soil infiltration capacity. The results obtained by the Shapiro–Wilk test and Welch’s test in irrigated and non-irrigated areas at individual dates showed statistically insignificant differences in three cases (IDM1, p = 0.123; IDM3, p = 0.382; IDM4, p = 0.445) and statistically significant in one case (IDM2, p = 0.0175). Based on the hypotheses and the results obtained, it can be said that the work tasks performed have a decisive influence on the infiltration capacity of the soil. The phenomenon of “water resistance” did not manifest itself in our research on soil infiltration capacity. The results were also evaluated using ArcGIS software 10.0 to display the spatial variability of soil hydraulic conductivity. The last application used to evaluate the results was Orange software 3.40.0, using clustering maps and hierarchical clustering. The results also pointed to variability depending on the dates of monitoring.

Pilot-scale pyrolysis requires joint assessment of product recovery and operational behavior. This exploratory study reanalyzed three Paulownia wood-chip runs at nominal setpoints of 300, 400 and 500 °C in a five-section reactor. Each condition processed a reported 20 kg wet-feed charge. Five-second timestamps defined a common 60 min window with 721 observations per run. Recovered solid masses were 7.3, 7.4 and 5.8 kg, and condensate masses were 9.1, 8.3 and 6.6 kg. Combined recoveries were 82.0, 78.5 and 62.0% of wet feed. Unadjusted gas-flow means were 1.757, 3.380 and 8.444 m³·h⁻¹, conditional on an undocumented flowmeter reference state. Temperature-channel d10 means 302.94, 398.43 and 497.72 °C. Elemental analysis revealed a substantial enrichment of carbon content in biochar, increasing from 46.2 wt.% in raw Paulownia biomass to a maximum of 76.99 wt.% at 400 °C. Concurrently, organic dry matter content decreased with increasing temperature due to progressive devolatilizations and ash concentration. The findings confirm that Paulownia biomass can be efficiently valorized through pyrolysis into products suitable for renewable energy production, carbon sequestration and agricultural and environmental applications, supporting its integration into circular bioeconomy systems.

The conversion of fast-growing non-food woody biomass into storable fuels and carbon-rich products may contribute to the diversification of regional renewable-resource systems. This exploratory pilot-scale study evaluated Paulownia wood chips in a continuously fed five-zone pyrolysis reactor at setpoint temperatures of 300, 400, and 500 °C. One 20 kg wet-feed run was evaluated at each setpoint at a nominal throughput of 20 kg h⁻¹ and a nominal residence time of 10 min. Reactor temperature, non-condensable gas volumetric flow, and electrical input power were recorded at 5 s intervals. Recovered biochar masses were 7.3, 7.4, and 5.8 kg, and recovered condensed-liquid masses were 9.1, 8.3, and 6.6 kg at 300, 400, and 500 °C, respectively. The combined solid-plus-liquid recovery decreased from 82.0 to 62.0% of wet feed. Because gas mass and composition were not measured, the remaining fraction cannot be interpreted as a gas yield, and a closed mass balance was not established. Mean non-condensable gas flow rates calculated from the time-series data were 1.65, 3.53, and 8.36 m³ h⁻¹, while mean measured reactor temperatures were 303.1, 398.5, and 498.0 °C. The highest observed carbon content and higher heating value of biochar occurred at 400 °C, at 76.99 wt.% and 30.47 MJ kg⁻¹. The calculated atomic H/C ratio decreased from 0.68 at 300 °C to 0.37 at 500 °C. The results describe temperature-dependent behaviour in one pilot-scale run per condition and do not provide inferential evidence of an optimum. Replicated reactor runs, gas chromatography, liquid-phase analysis, and expanded biochar characterisation are required before process efficiency or application suitability can be established.