High-performance liquid chromatography (HPLC) with size exclusion (SEC) separation function was used to isolate and examine the molecular mass (MM) distributions and polydispersity of humic substances (HSs) and dissolved organic matter (DOM) from mineral soils and peats. The aim was to improve their detailed characterisation and to inform of their soil carbon (C) sequestration and environmental quality. This is the first study conducted in Lithuania in which HSs and DOM, separated from two soil types, have been used to characterise soil at the molecular level. The HPLC-SEC, as a separation method, was coupled with diode-array detection (DAD), thus enabling the separation of molecular fractions. Results showed that HPLC-SEC can be used to determine the MM of HSs in soil, provided that the relation between retention time and MM is known and a suitable method for fitting the HS peak is available. The UV-spectra analysis showed that DOM has a larger MM (M_w = 2439–3436 Da), which contains more aliphatic C. The HS fraction has a smaller MM (M_w = 2776 Da), with aromatic structures that reflect a higher aromaticity. Separated fractions had characteristic MMs of humic acid (HA) and fulvic acid (FA) and DOM. The HSs separated from peat samples were characterised by higher aromaticity, humification and stability. The HSs extracted from mineral soil samples showed a higher degradability level. The results also show the MM distribution and polydispersity of HS and DOM fractions (M_w/M_n = 1.009–1.252) are relatively homogenous in both soil types. Findings confirm that chromatographic and spectrometric parameters can be used for characterisation of both HSs and DOM, and for detecting changes in organic matter quality. Moreover, they can also be used for a further understanding the C-cycle and could be applied for enhancing soil C-sequestration and informing environmental quality management.

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 (N_min) 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 (N_min 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.

This study aimed to investigate the productivity of two C3 legumes – alfalfa (Medicago sativa L.) and fodder galega (Galega orientalis Lam.) – and the feasibility of their use as renewable energy resources. Maize (Zea mays L.), a well-established bioenergy crop belonging to the C4 plant group, was used as a baseline in comparison. Field trials were conducted at the Institute of Agriculture at the Lithuanian Research Centre for Agriculture and Forestry during the period 2012–2013. The perennial forage legumes were grown without mineral or organic fertilizers. The maize was grown (a) without and (b) with nitrogen fertilizers. The perennial forage legumes were harvested three times per growing season. Carbon (C), nitrogen (N) and sulphur (S) contents of biomass were determined by using a dry combustion method. The calorific value of biomass was determined by a combustion method using an IKA bomb calorimeter. The largest share of the total annual yield of biomass of perennial forage legumes was obtained from the first cut and amounted to 54% and 57% for alfalfa and fodder galega, respectively. The S content of biomass was similar in all crops investigated, but the N content was higher in perennial forage legumes. Biomass C content did not differ between the crops, but the C:N ratio was widely varied – from 28–35 in fertilized maize, to 16–17 in alfalfa and 15–16 in fodder galega. This study showed that alfalfa and fodder galega can be grown as energy crops under less intensive management; however, the specific chemical composition of biomass should be considered before choosing the most appropriate conversion process.

The aim of this study was to determine changes in the morphological, physical and chemical properties of Retisols caused by their agrogenic transformation. The study carried out on Retisols on relatively natural and agrogenically affected land in 2016. Soil samples taken from the genetic horizons of all profiles to measure soil organic carbon, pH, hydromorphic and physical properties. Due to long-term, deep ploughing, the sequence of soil horizons in the Retisol profile had changed from O-Ah-El-ElBt to Ahp-ElBt. Intensive soil liming changed chemical properties and morphological features of Retisol. The clay and silt particles leached out of from the Ah and El horizons to the deeper layers due to illuviation and podsolization. The content of SOC in the 0-30 cm layer of the Ah horizon of agrogenically affected Retisol was 1.0%, and in the forest Retisol - 1.7%; however, forest Retisol was more acidic. Ploughing and no tillage management caused a reduction in total porosity, water holding capacity and plant available water content compared with the other land-uses. We conclude that the use of ploughless tillage on Retisol is not identical to the conditions of natural soil formation and soil fertility maintenance.