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This study aimed to evaluate the impact of total humic extract (THE) and complex mineral fertilizer N 5 P 15 K 25 enriched with humic substances (HS) 0.5% on moraine loam soil properties and crop productivity. The field experiment was performed in Western Lithuania (55°43ʹ N, 21°27ʹ E) at Vėžaičiai Branch of the Lithuanian Research Centre for Agriculture and Forestry in 2015-2017. Experimental object: THE 16.5%, which contains 13.2% humic acids, 3.3% fulvic acids and 5.5% potassium oxide (K 2 O), and complex mineral fertilizer N 5 P 15 K 25 enriched with HS 0.5% consisting of humic and fulvic acids. The soil of the experimental site was moraine loam Bathygleyic Dystric Glossic Retisol. The experiment included the following treatments: 1) unfertilized (control), 2) NPK + THE 20 L ha-1 , 3) NPK traditional, 4) NPK 400 kg ha-1 with HS 0.5% and 5) NPK 200 kg ha-1 with HS 0.5%. The experimental data indicated that the application of NPK + THE 20 L ha-1 or complex mineral fertilizers NPK 400 and 200 kg ha-1 with HS 0.5% additives tend to mitigate moraine loam soil acidification and to contribute more to the formation of water-stable aggregates in the topsoil compared with NPK traditional. The both rates of mineral NPK fertilizers enriched with HS 0.5% significantly (by 1.8-2.1 times) increased the content of water-soluble phosphates in the topsoil compared with unfertilized soil. The highest amount of water-extractable organic carbon and the greatest soil biological activity were determined in the soil after incorporation of 400 and 200 kg ha-1 of mineral fertilizers enriched with HS 0.5%. In terms of crop yield, soil enrichment by mineral fertilizers (400 and 200 kg ha-1) with HS 0.5% additives and by the NPK + THE 20 L ha-1 was superior to NPK traditional fertilization.

In this study, the nitrogen-fixing, Gram-negative soil bacteria Rhizobium anhuiense was successfully utilized as the main biocatalyst in a bacteria-based microbial fuel cell (MFC) device. This research investigates the double-chambered, H-type R. anhuiense-based MFC that was operated in modified Norris medium (pH = 7) under ambient conditions using potassium ferricyanide as an electron acceptor in the cathodic compartment. The designed MFC exhibited an open-circuit voltage (OCV) of 635 mV and a power output of 1.07 mW m−2 with its maximum power registered at 245 mV. These values were further enhanced by re-feeding the anode bath with 25 mM glucose, which has been utilized herein as the main carbon source. This substrate addition led to better performance of the constructed MFC with a power output of 2.59 mW m−2 estimated at an operating voltage of 281 mV. The R. anhuiense-based MFC was further developed by improving the charge transfer through the bacterial cell membrane by applying 2-methyl-1,4-naphthoquinone (menadione, MD) as a soluble redox mediator. The MD-mediated MFC device showed better performance, resulting in a slightly higher OCV value of 683 mV and an almost five-fold increase in power density to 4.93 mW cm−2. The influence of different concentrations of MD on the viability of R. anhuiense bacteria was investigated by estimating the optical density at 600 nm (OD600) and comparing the obtained results with the control aliquot. The results show that lower concentrations of MD, ranging from 1 to 10 μM, can be successfully used in an anode compartment in which R. anhuiense bacteria cells remain viable and act as a main biocatalyst for MFC applications.

Given the growth in the number of biogas power plants and the increase in the generation of waste from energy production, it is relevant to study the sustainable nature of this waste. Digestate is a product of the anaerobic digestion process, and is a valuable bio-fertilizer containing organic matter and nutrients necessary for agricultural plants’ growth. The study showed that different rates of liquid and solid phases of anaerobic digestate influenced the contents of carbon and nitrogen in genetically young soil in alluvial deposits—Fluvisol. The application of solid digestate (SD) considerably increased soil organic carbon content (SOC) in the 0–10 cm soil layer; however, SOC did not reach the 20–30 cm layer. Liquid digestate (LD) significantly increased SOC in the deeper layers. The levels of mineral nitrogen (Nmin) and water extractable organic carbon (WEOC) increased in the 0–10 cm soil layer soon after fertilization with LD and SD. The mobile components of the soil (Nmin and WEOC) were characterized by high variability during the growing season. Within the 2-month period, their concentrations decreased drastically and were close to those of unfertilized soil. The research indicates that anaerobic digestate had a greater effect on mobile forms of carbon and nitrogen in the soil than on their total amounts.

Relationships between different microorganisms’ groups and the soil environment are reversible, and the state of the soil and its provided services can also change the structure and abundance of microorganisms as well as that microorganisms can affect soil conditions. The aim of our research was to analyze the physical and chemical properties of differently formed agroecosystems, which are affected by different anthropogenic pressures and to compare how bacterial composition differ in totally different environments. It was established that different soil microorganisms’ physiological groups significantly correlated with chemical and physical soil properties: atmospheric nitrogen-fixing bacteria showed a positive correlation with soil pHKCl, Nsum, P2O5, and soil bulk density; meanwhile, soil porosity, and the K2O amount in the soil negatively affected the population of atmospheric nitrogen-fixing bacteria. The same tendencies were inherent to actinomycetes and ammonifying bacteria. Micromycetes showed a negative trend with soil pHKCl, showing that soils with lower pHKCl are characterized by a higher abundance of micromycetes. Analysis of the taxonomic diversity of soil microbes reveals that the bacterial communities were dominated by two main species of bacteria: Betaproteobacterium and Candidatus Saccharibacteria. Bacterial identification shows that the main bacterial species were the same in all analyzed sampling places despite the different anthropogenic activities, parent material, and other abiotic conditions. Only a few species were identified in different soil groups, and it may be assumed that those groups could be potential bioindicators for specific soil types, but more in depth research is needed to confirm this hypothesis.

This study is designed to evaluate soil organic matter (SOM) quality indicators: molecular indicators of dissolved organic matter (DOM) and hydrophobicity of humic acid (HA), distribution of quantity in humified and labile fractions of histosols during renaturalization. The aim is to determine the differences in the qualitative composition of humic acids at the molecular level, which are decided by the previous tillage and genesis, and to evaluate the impact of anthropogenization on the peat soil according to hydrophobicity, as well as to estimate the impact of soil genesis and removing peat layer. Soil samples were taken from the three Sapric Histosol (according to WRB2022) profiles and the 0–30 cm layer in three field replicates (Lithuania, Radviliskis mun.). Our study suggested that in the differently managed drained Sapric Histosol under renaturalization, the most significant changes occurred in the topsoil layer (0–30 cm), in which an increase in the content of SOM particles 106–2 µm in size. It is expedient to grow perennial grasses and legumes to maintain the soil organic carbon stability mobile humic acids to mobile fulvic acids ratio (MHA:MFA 0.83 to 0.86). An evaluation of the quality of HA (E4:E6) revealed their highest maturity in the unfertilized perennial grasses (3.88) and crop rotation (3.87) with grasses. The highest concentrations of hydrophilic groups (ratio of the C=O to O-H) were found in Sapric Histosol under deciduous hardwood forest (12.33). The lowest hydrophilicity (9.25 and 9.36) was of the crop rotation Sapric Histosol with removed peat layer. The most sustainable use of drained Sapric Histosol in the context of the sustainability and quality of its humus substances should be associated with the formation of perennial grass and clover grassland and the cultivation of deciduous hardwood. Therefore, the horizon forms on the top part of the profile, which protects deeper Histosolic material layers from its mineralization.

The development of new high-power biofuel cells has been limited in the past by slow or indirect charge transfer. In this study, enzymatic biofuel cell (EBFC) systems were explored with different materials used to evaluate their applicability as redox mediators. Redox mediators of different natures have been selected for this research. Cytochrome c, Chlorophyll a, and supernatant of ultrasonically disrupted algae Chlorella vulgaris cells were examined as potential redox mediators. The effect of heparin on the EBFC was also evaluated under the same analytical conditions. The measurements of open circuit potential (OCP) and the evaluation of the current response in two modes of measurement were performed (i) during potential cycling in cyclic voltammetry measurements or (ii) at the constant potential value in chronoamperometry, and were applied for the evaluation of EBFC. Cytochrome c, Chlorophyll a, and the supernatant of ultrasonically disrupted algae Chlorella vulgaris cells-based redox mediators were efficient in the glucose oxidase (GOx) based EBFC. Electron transfer from GOx to the electrode was facilitated through the redox mediators adsorbed on the electrode. Electrodes modified with Chlorophyll a- and Cytochrome c-based redox mediators were suitable for the development of glucose biosensors. This was demonstrated by increasing the glucose concentration within 0 mM–100 mM in the system, the current density increased, and the system reached equilibrium rather faster regarding the electrochemical reaction. The power density is an important feature in revealing the action of biofuel cells. The highest power values were generated by the systems based on the application of redox-mediated Chlorophyll a and the supernatant of ultrasonically disrupted Chlorella vulgaris cells. The surface power density was about 2.5–4.0 µW/cm2. Control of a study was performed with a polished graphite electrode and the maximum surface power density was 0.02471 µW/cm2.

Soil pH influences the composition and activities of microbial communities, which are driving the transformations of soil organic carbon (SOC). However, the effect of liming on SOC sequestration remains controversial. Evaluation of the effect of liming on SOC and humified carbon fractions was one of the most important tasks of this work. Studies were carried out in the long-term field experiment using slaked-lime rates of 0.5 or 2.0, depending on the soil hydrolytic acidity. It was determined that liming did not increase SOC content, but led to redistribution of SOC. The amount of mobile humic acids in the soil decreased while the intensity of liming increased. When liming at the 2.0 rate, the lowest HA1 level (0.251 g kg−1 C) and highest amount of HA2 (0.21 g kg−1 C) were found. It could be stated that soil liming, as a measure, allows the stabilization of HA and FA by the cation bridging mechanism. Liming resulted in slower mineralization of SOC and at the same time it also resulted in carbon sequestration in the form of valuable humic acids. An important consistent pattern of carbon transformation was identified in this study and can be applied in selecting of the most suitable combination of agricultural practices, promoting carbon sequestration and soil fertility.