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Abstract Soil plays a crucial role in carbon sequestration in terrestrial ecosystems. It is known that the strengthening of carbon sequestration processes occurs with a decrease in the intensity of soil treatments. The study of changes in organic matter and physical properties of sod-podzolic soil 16 years after the transition from arable soils to a fallow state against the background of weak water erosion was carried out. A significant increase in the content and reserves of total carbon in fallow soil compared to arable soil was found, mainly due to carbon of the light fraction. On arable soil, the content of the light fraction in the lower part of the field was significantly higher than in the upper part, due to the washing away of light particles as a result of erosion, these differences were smoothed out on fallow soil. There are no significant changes in the density, density of the solid phase and total porosity in fallow soil at this stage of succession, compared with arable soil. In fallow soil, the content of macro-aggregates (including water-bearing ones) was noticeably higher, and the share of micro-aggregates was lower than in arable soil.

Research objective is to address an up to date task of developing the technology of associated gold recovery from complex ore. Object of research is the gold-bearing copper-pyrite ore. Gold was recovered in laboratory conditions with the use of gravity methods of mineral separation. Research tools. Rational modes of machinery operation have been determined through mathematical planning of experiments including the obtained results processing by mathematical and statistical methods. Methods of research. Gold was recovered in the grinding-classification circuit based on a seriesinstalled short-cone hydrocyclone, a jigging machine and a shaking table. Research results. The developed jig mode differs from the existing ones by the closed-circuit of jig machine chambers: from the feed of the second (in the direction of the light fraction travel) jig chamber, the light fraction (tailings) and undersize product – fraction with the increased content of accessory minerals (rough concentrate) are separated. The rough concentrate in the second chamber is directed to the first chamber of the machine, where the finished jig concentrate is obtained in the form of an undersize product. The light fraction moves from the first chamber to the second and is removed from the machine through the tail board. When fine-tuning the heavy fraction of jigging on a shaking table, it is recommended to mix 1/2 part of the initial feed of the tables with the rough concentrate isolated from the other 1/2 of the original feed. The new jigging mode and the scheme of concentration on the tables provide an increase in the gold content in the initial feed of the apparatus, which is the reason for a decrease in gold losses with the tails of the gravity circuit. Research relevance. Gold recovery increment by 4.77% was obtained due to the use of all three recommended scientific and technical measures, namely sands concentration in a short head cone crusher on a jig, switching the jig chambers to a closed circuit, and jet motion of concentrates on shaking tables. Scope of the results. The results should be applied when concentrating ore containing free (amalgamable) gold, as well as gold-bearing pyrite.

The properties of black carbon (BC) are described very differently in the literature, even when determined by the same methodological procedure. To clarify this discrepancy, BC was investigated in the clay Cambisols of southern Bohemia, Czech Republic, in groups of soils with lower and higher deposition of its atmospheric fallout. The BC determination was performed according to a modified method of Kuhlbusch and Crutzen (1995). The amount of the free light fraction, the occluded light fraction of soil organic matter and its ratio, the amount of heavy soil fraction DF, and its soil organic matter DFOM were determined. Other soil characteristics were identified. It was found that there are two very different types of BC in soils. Historical BC from biomass fires, and new, anthropogenic, from the furnace and transport fumes. Historical BC has a significant effect on the organic matter of the heavy soil fraction, on the ratio of the free and occluded soil organic matter fraction, and the number of water-resistant soil aggregates. Anthropogenic BC does not have this effect. Because this form of BC is not significantly stabilized by the colloidal mineral fraction, it is necessary to take general data on BC’s high stability and resistance to mineralization in the soil with circumspection.

Cultivating crops influences soil organic matter (SOM), but the effect of different crops remains unclear, particularly under long-term monocropping. The objective of this study was to identify how different crops influence the content and chemical structures of SOM under long-term monocropping. Here, soils were sampled (0–20 cm) under 27-year soybean and maize monocropping and separated into different physical fractions. The content and chemical structures of SOM in all fractions were determined. SOM contents were higher under soybean than maize in bulk soil and macroaggregates and their light-fractions instead of microaggregates and silt and clay. The difference in SOM chemical structure was observed in aggregates and density fractions rather than bulk soils and supported by the result of principal component analysis. The proportion of O-alkyl C in macro- and microaggregates and all free light fractions and that of aromatic C in mineral-associated fractions were higher, while that of carbonyl C was lower under maize than soybean. These results demonstrated that different crops monocropping influences the content and chemical structures of SOM, and the variations were mainly in the light-fraction SOM and highlight a higher sensitivity of physical fractions than bulk soil to different crops.  

Microbially mediated soil organic matter is an extremely sensitive pool that indicates subtle changes in the quality parameters responsible for the soil’s ecological and productive functions. Fifty years of mineral fertilization of a wheat-corn cropping system has a strong impact on soil quality parameters. The goal of the research was to study the dynamics and quality of soil biological parameters affected by increasing amounts of mineral nitrogen. Soil respiration, potentially mineralizable C and N, microbial biomass C and N and light-fraction OM on Cambisol were analyzed in the following treatments: (1) Control (without fertilization); (2) NPK (60/51/67); (3) NPK (90/51/67); (4) NPK (120/51/67); (5) NPK (150/51/67 kg ha−1). The parameters studied were significantly affected by the long-term application of mineral fertilizer compared with both the control and the adjacent native soil. The highest amounts of nitrogen (N150) did not significantly differ from N120 and N90 for most of the parameters studied. Potentially mineralizable C represented the largest labile carbon pool, while microbial biomass N was the largest labile nitrogen pool. The mineralization rates for C and N were oppositely distributed over the seasons. The sensitivity index correlated with the amount of light-fraction OM. The results give a deeper insight into the behavior and distribution of different pools of labile SOM in the agro-landscapes and can serve as a reliable basis for further research focused on zero soil degradation.

Plant roots and the organisms that surround them are a primary source for stabilized organic C, particularly in grassland soils, which have a large capacity to store organic carbon belowground. To quantify the flow and fate of plant fixed carbon (C) in a Northern California annual grassland, we tracked plant carbon from a five-day 13CO2 pulse field labeling for the following two years. Soil and plant samples were collected immediately after the pulse labeling, and again at three days, four weeks, six months, one year, and two years. Soil organic matter was fractionated using a sodium polytungstate density gradient to separate the free-light fraction (FLF), occluded-light fraction (OLF), and heavy fraction (HF). Using isotope ratio mass spectrometry, we measured 13C enrichment and total C content for plant shoots, roots, soil, soil dissolved organic carbon (DOC), and the FLF, OLF, and HF. The HF was further analyzed by solid state 13C NMR spectroscopy. At the end of the labeling period, the largest amount of 13C was recovered in plant shoots (60%), but a substantial amount (40%) was already found belowground in roots, soil, and soil DOC. Density fractionation of 4-week soil samples (from which living roots were removed) indicated that the highest isotope enrichment was in the mineral-rich heavy fraction, with similar enrichment of the FLF and OLF. At the 6-month sampling, after the dry summer period during which plants senesced and died, the amount of label in the FLF increased such that it was equal to that in the HF. By the 1-year sampling, 13C in the FLF had declined substantially and continued to decline by the 2-year sampling. 13C recovery in the OLF and HF, however, was qualitatively stable between sampling times. By the end of the 2-year experiment, 69% of remaining label was in the HF, 18% in the FLF and 13% in the OLF. While the total 13C content of the HF did not change significantly from the 4-week to the 2-year sample time, 13C NMR spectroscopic analysis of spring HF samples from 2018, 2019, and 2020 suggests that the relative proportion of aliphatic/alkyl functional groups declined in the newly formed SOC over the 2-year period. Simultaneously, aromatic and carbonyl functional groups increased, and the proportion of carbohydrate groups remained relatively constant. In summary, our results indicate that initial associations between minerals and root-derived organic matter are significant and form rapidly; by 4 weeks, a substantial amount (17%) of the total plant-derived 13C had become associated with the heavy fraction (HF) of soil. While the majority of annual C input cycles rapidly (<2-year timescale), a sizeable proportion (~12% of the original inputs) persisted for 2 years.

A study on light fraction organic matter was carried out on soil where leafy biomass of Enterolobium cyclocarpum (ENCY), Treculia africana (TRAF), Anogeissus leiocarpus (ANLE), Gliricidia sepium (GLSE), Leuceana leucocephala (LELE) were used as mulch. Soil samples were collected in each plot at two auger points 0-15 cm and 15-30 cm and then homogenized for laboratory analysis. ANLE was observed to have significant higher values (6.37, and 6.52) on soil pH, and at day 28 on soil pH respectively. Light fraction organic carbon (LFC) also experienced significant higher value (3.48 g/kg) at day 28 in ANLE leafy biomass. However, LELE had the significant highest values (0.37 g/kg, and 1.44 g/kg) on light fraction nitrogen (LFN), and at day 42 on LFN respectively, while, microbial population count (MP) was highest in ENCY (183516667 cfu/g), and (726666667 cfu/g) at day 14 respectively. It is therefore concluded that the leafy biomass investigated had improving positive effects on light fraction organic matter. Keywords: Organic matter, Soil content, Light fraction, Leafy biomass, Tree species

The aim of the study was to determine the effect of stand species composition on PAHs accumulation. The study covered the soils of the stands of the Rybnik Forest District, which are under the influence of one of the highest deposition of industrial emissions in Europe. Pine, pine-oak and oak stands growing in the same soil conditions were selected for the study. Samples for further analyses were collected from the organic horizon, from the humus mineral horizon and from the mineral horizon. Organic C content, N content, pH, alkaline cation content, as well as microbiological biomass of C, N, extracellular and intracellular enzyme activity were determined in the soil samples. PAH content was determined in the soil samples. Additionally, the soil organic matter fractions were determined: free light fraction (fLF), occluded light fraction (oLF) and mineral associated fraction (MAF). Pine stand soils were characterized by the highest average PAHs content. The oak stand soils were characterized by the lowest PAHs accumulation and high enzymatic activity. The study confirms the important role of the stand species composition in shaping the quality and quantity of SOM and soil acidification, which in turn is reflected in microbial activity and PAHs accumulation in forest soils. PAHs accumulation in forest soils is related to the fractional composition of SOM, which is the effect of the influence of species composition through the supplied aboveground and belowground biomass. A strong correlation between the PAH content and C content of the light soil fraction of OM was noted.