In drought-prone regions without irrigation systems, effective agrotechnologies such as subsoiling are crucial for enhancing soil infiltration and water retention. However, the effects of subsoiling can vary depending on crop type and environmental conditions. Despite previous research, there is limited understanding of the contrasting responses of C3 (sunflower) and C4 (maize) crops to subsoiling under drought stress. This study addresses this knowledge gap by assessing the effectiveness of subsoiling as a drought mitigation practice on Haplic Chernozem in Northern Bulgaria, integrating ground-based and remote sensing data. Soil physical parameters, leaf area index (LAI), canopy temperature, crop water stress index (CWSI), soil moisture, and yield were evaluated under both conventional tillage and subsoiling for the two crops. A variety of optical and radar descriptive remote sensing products derived from Sentinel-1 and Sentinel-2 satellite data were calculated for different crop types. Consequently, the use of machine learning, utilizing all the processed remote sensing products, enabled the reasonable prediction of LAI, achieving a coefficient of determination (R²) after a cross-validation greater than 0.42 and demonstrating good agreement with in situ observations. Results revealed differing responses: subsoiling had a positive effect on sunflower, improving LAI, water status, and slightly increasing yield, while it had no positive effect on maize. These findings highlight the importance of crop-specific responses in evaluating subsoiling practices and demonstrate the added value of integrating unmanned aerial systems (UAS) and satellite-based remote sensing data into agricultural drought monitoring.

Soil structure has an important role in storing and transporting substances, providing natural habitats for soil microorganisms, and allowing chemical reactions in the soil. A complex investigation on factors affecting soil structure characteristics under herbaceous (H), deciduous (D), mixed (M), and coniferous (SP—Scots Pine and NS—Norway Spruce) vegetation was conducted at three experimental stations—Gabra, Govedartsi, and Igralishte, located correspondingly in the Lozenska, Rila, and Maleshevska Mountains in South-West Bulgaria. The data set obtained includes soil structure indicators and physical, physicochemical, chemical, mineralogical, and microbiological parameters of the A and AC horizons of 11 soil profiles. Under different vegetation conditions, soil structure indicators respond differently depending on climatic conditions and basic soil properties. Regarding the plant available water capacity (PAWC), air capacity (AC), and water-stable aggregates (WSAs), the surface soil layers have an optimal structure in Gabra (H, D), Govedartsi (H, SP, NS), and Igralishte (H). The values for the relative field capacity (RFC < 0.6) showed that the studied soils were water-limited. The WSAs correlated with SOC in Gabra, while in Govedartsi and Igralishte, the WSAs correlated with the β-glucosidase known to hydrolyze organic carbon compounds in soil. The information obtained is important for soil quality monitoring under climatic and anthropogenic changes.

Soil contamination with heavy metals (HM) poses a risk to human health and can impact different soil functions. This study aimed to determine the influence of heavy metal pollution on the physical and physicochemical characteristics of the two profiles of alluvial–deluvial soil under grassland located at different distances from the Aurubis-Pirdop Copper smelter in Bulgaria. Data for soil particle-size distribution, soil bulk and particle densities, mineralogical composition, soil organic carbon contents, cation exchange properties, surface charge, soil water retention curves, pore size distribution—obtained by mercury intrusion porosimetry (MIP)—and thermal properties were obtained. The contents of Pb, Cu, As, Zn, and Cd were above the maximum permissible level in the humic horizon and decreased with depth and distance from the Copper smelter. Depending on HM speciation, the correlations are established with SOC and most physicochemical parameters. It can be concluded that the HMs impact the clay content, specific surface area, distribution of pores, and the water stability of soil aggregate fraction 1–3 mm to varying degrees.

The thermal properties of soils can be influenced by additives of different origins (non-organic, organic and mineral) and roles in soil quality. This study aims to evaluate the effects of microplastics, vermicompost, and zeolite on the thermal properties of two soil types using a combination of experimental data and modeling approaches. Laboratory experiments were conducted using surface layer samples of a clay soil (Vertic Phaeozem) and a loam soil (Haplic Cambisol). Each additive was applied at a mass ratio of 10% to the soil samples. The thermal conductivity (λ), thermal diffusivity (D) and volumetric heat capacity (Cv) were measured with the SH1 sensor of a KD2Pro device during the drainage process of the soil samples at different matric potentials. The relationships between λ, Cv, D, gravimetric water content, and matric suction (h) were analyzed using linear and polynomial regression models (for Cv and D) and a closed-form equation (for λ). The fitted models exhibited small errors, such as a root mean square error (RMSE) of 0.03-0.06 W m-1 K-1, and high coefficient of determination R2>0.9. The effects of the different additives on water retention, λ, Cv and D were found to be specific to each soil type and depended on the properties of both the soil and the additives. These findings highlight the significance of additives in modifying soil thermal properties and emphasize the importance of considering the interactions between soil characteristics and additive properties. The combination of experimental data and modeling approaches provides valuable insights into understanding the complex dynamics of soil thermal properties and the potential impacts of additives on soil functionality and quality.

The effect of additives of different composition and origin - non-organic (microplastics), organic (vermicompost) and mineral (zeolite) on microflora and soil physical conditions of two soil varieties was studied. A laboratory experiment was performed on soil samples, taken from the surface (0-20 cm) soil layer of Vertic Phaeozem (clay textural class), from the experimental field Gorni Lozen under grassland and of Haplic Cambisol (loam textural class), from the experimental station of potatoes Samokov, cultivated land. The concentrations of the additives were 10% by mass of the sample. The amount of main groups of soil microorganisms was determined - ammonifying and cellulolytic microorganisms, mineral nitrogen-utilizing bacteria, actinomycetes and microscopic fungi. The changes of water retention properties of the studied mixtures were analyzed. It was found that the distribution of soil microorganisms was influenced in a different way by the applied additives in the studied soils.