This article aims to explore the use of machine learning (ML) methods for mapping the distribution of mercury (Hg) content in topsoil, using the city of Ufa (Russia) and adjacent areas as an example. For this purpose, a soil dataset of 250 points sampled from a 0–20 cm depth on different land uses, including residential, industrial and undisturbed (forests and parks), was used. Random Forest (RF), Extreme Gradient Boosting (XGboost), Cubist and k-Nearest Neighbor (kNN) ML techniques were employed to model and map the Hg concentrations. We used remote sensing data (RSD) and topographic attributes as explanatory variables. ML models were calibrated and validated using the leave-one-out cross-validation approach. The Hg content varied from 0.005 to 0.58 mg/kg and was characterized by very high variability. According to the MAE and RMSE metrics, the RF method resulted in the most accurate spatial prediction for the Hg content (0.029 and 0.065 mg/kg, respectively), while the XGBoost approach showed the lowest prediction efficiency (0.032 and 0.073 mg/kg, respectively). The results showed that the slope map, spectral index MSI and Sentinel-2A band B11 were the key variables in explaining the variability of Hg content. We found that higher uncertainty values of soil Hg were found in croplands, urban residential and industrial areas, which supports the view that spatial modelling of HM in urban landscapes is challenging. The present study provides insights into the potential of digital soil mapping techniques in combination with RSD and terrain variables for identifying areas at risk of Hg contamination in urban areas, which can inform land-use planning and management strategies to protect human health and the environment.

To reduce the use of commercial conventional inorganic fertilizers, the possibility of using pulp and paper industry wastes in agriculture as an alternative source of nutrients is recently under study and discussion. This work aimed to evaluate the effect of sodium lignosulfonate application to soil on photosynthetic leaf nutrient (N, P, K, Ca, Mg, Fe, Mn, and Na) and water use efficiency. A pot culture experiment was conducted with cucumber seedlings, using five lignosulfonate concentrations (0, 1, 2.5, 5, and 10 vol. %) in sandy soil under sufficient or low nutrient availability for plants. The impact of nutrient availability on the plants’ physiological traits was stronger than the lignosulfonate impact. Under sufficient nutrient availability, the lignosulfonate application resulted in decreased photosynthetic N, P, K, Ca, Mg, Fe, and Na use efficiency. Cucumber growth and development, and photosynthetic nutrient, water, and light use efficiency were significantly reduced with a nutrient deficiency. The sodium lignosulfonate application was not successful in eliminating the negative effects of nutrient deficit on cucumber seedlings.

The possibility of using brown algae in agriculture as an alternative source of nutrients is currentlyunder study and discussion. Our study aimed to evaluate the effect of F. vesiculosus on the agrochemical properties of four soil types: Retisol loamy sand soil, Retisolloam, Retisol clay, and Histosol. The F. vesiculosus waste was added to soil samples at a rate of 0, 0.5, 1.0, 2.0, 5.0, and 10 wt%. The brown algaewaste application significantly decreased soil acidity in the substrates of all soil types, with the larger increasesfor Retisol loamy sand and Retisol clay than for Retisol loam and Histosol. The application of F. vesiculosus waste products increased the C content in all soil types except Histosol. The N and P content in soil substrates were not significantly affected by algaewaste application regardless of soil type. This study showed that the effect of F. vesiculosus waste application varies depending on the soil type, with the strongest impact on Retisol clay and the lowest on Histosol.

The results of a long-term study of changes in soils and vegetation during postagrogenic succession of sown meadows on reclaimed peat soils (Eutric Histosols) are presented. The study was performed on experimental plots in the Korzinskaya Lowland (Karelia); sowing of perennial grasses was accompanied by the application of mineral fertilizers. Observations over changes in the vegetation communities along with the reduction of the peat thickness were conducted. The soil samples were analyzed for the organic carbon, total nitrogen, and available phosphorus contents and for the pH of salt extracts. Vegetation was described using the Braun-Blanquet approach; the botanical composition and the biomass of herbs were assessed by their cutting and weighing. Nematode communities were characterized by their taxonomic diversity, population density, and eco-trophic structure. The analysis of soil profiles demonstrated that the thickness of the peat deposits decreased over 40 years of observation (1974–2015). The direction of vegetation succession on sown meadows was dictated by the type of fertilization. Two plant communities were formed: Deschampsieta caespitosae humidiherbosum developed on the plots treated with mineral fertilizers, and Elytrigeto magnograminosoherbosum community developed on the plots treated with mineral and organic fertilizers. The main changes in soil nematode communities during the long-term succession were related to their eco-trophic structure. Two trophic groups exhibited an obvious response: the relative abundance of nematodes associated with plants decreased, whereas the share of plant-parasitic nematodes increased. In addition, it was found that the species composition of herbs predetermined the ecological specialization of dominant plant-parasitic nematode taxa.

To eliminate the negative effect of soil contamination with heavy metals on plant growth and crop yield, different methods and techniques are the subject of discussion and study. In this study, we aimed to evaluate the effect of secondary pulp and paper-mill sludge application to soil on the response of the main physiological processes such as the growth, photosynthesis, and respiration of lettuce (Lactuca sativa L.) plants to soil contamination with Pb. For the pot experiment, Pb was added to sandy loam soil at concentrations of 0, 50, and 250 mg Pb(NO₃)₂ per kg of the soil, and secondary sludge was added to a 0, 20, or 40% sludge solution during each plant watering. The Pb-mediated change in plant biomass allocation, decrease in the photosynthetic rate, increase in leaf respiration rate, and the degree of light inhibition of respiration were closely associated with increases in both root and shoot Pb content. For the Pb-free soil condition, secondary sludge application contributed to the allocation of plant biomass towards a greater accumulation in the shoots than in the roots. Although stomatal opening was not affected by either Pb or sludge, sludge application increased photosynthetic CO₂ assimilation regardless of soil Pb content, which was associated with an increase in the electron-transport rate and carboxylase activity of Rubisco. Soil contamination with Pb significantly increased the ratio of respiration to photosynthesis, reflecting a shift in the carbon balance toward carbon losses in the leaves, but sludge application modified the coupling between the processes with a decrease in the proportion of respiratory carbon losses. The sludge-mediated recovery of the physiological processes of L. sativa reflected an increase in plant tolerance to soil contamination with heavy metals, the formation of which is associated with plant and soil adjustments initiated by secondary sludge application.