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.

The influence of biochar on the microflora in reclaimed soils from the area of the Medet mine, part of Asarel-Medet metallurgical plant, under the conditions of a 6 month incubation experiment, was evaluated. Four levels of biochar addition were studied 1%, 5%, 10% and 20%. Biochar positively affected the ammonifying microorganisms and mineral nitrogen-utilizing bacteria. On at the sixth month there was a significant increase in the amount of microorganisms associated with the processes of mineralization and ammonification. Actinomycetes have a greater distribution on the 3rd month along a 6 month period, but they exceeded the amounts of the control variants. Biochar favors the development of microscopic fungi and during both stages of the study they show a significant increase. The high percentage of biochar in the variants T4 and T7 suppresses the abondance of cellulose-decomposing microorganisms.

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.

A key objective of contemporary agriculture is to restore biodiversity, preserve ecosystem health, reduce the effects of climate change, and produce safe and healthy foods. Maintaining high soil fertility while reducing greenhouse gas emissions requires a precise assessment of how fertilization and crop rotation affect the carbon and nitrogen cycles in agroecosystems. In the context of a long-term fertilizer experiment on Luvic Chernozem, a monitoring of chemical and microbiological soil properties and CO2 emission was carried out. The fertilization treatments that have been continuously applied for 64 years under four-crop (wheat, barley, corn, and beans) rotation are N, P, K, NP, NK, PK, NPK, and 0. The highest organic carbon content was observed in the treatments NPK (1.42%) and NP (1.43%), and the lowest in the control (1.05%). The constant application of nitrogen as single fertilizer led to lower SOC values (1.22%). On average, CO2 emissions were the most intensive in NP (66.34 kg ha-1 day-1), NPK (67.82 kg ha-1 day-1) and PK (60.16 kg ha-1 day-1) treatments. The nitrogen fertilizer application most significantly alters soil properties including pH, EC, and SOC, which alters the environment for soil microbial development and influences the number and composition of soil microbial communities.

The key objectives of contemporary agriculture are restoring biodiversity, preserving ecosystem health, reducing the effects of climate change, and producing safe and healthy foods. Maintaining high soil fertility while reducing greenhouse gas emissions requires a precise assessment of how fertilization and crop rotation affect carbon and nutrient cycles in agroecosystems. Fertilization affects soil conditions, which alters the environment for soil microbial development and influences the number and composition of soil microbial communities, leading to changes in nutrient and carbon cycling. There is a lack of long-term experimental data on the impact of fertilizer treatments on soil CO₂ emissions, soil microbial communities, and their interactions. The novelty of this study is that it identified the fertilization effects on soil carbon sequestration, soil properties, and microbial communities in the context of a long-term fertilizer experiment in Luvic Chernozem. The fertilization treatments that were continuously pplied for 64 years under a four-crop (wheat, barley, corn, and bean) rotation were nitrogen (N), phosphorus (P), potassium (K), NP, NK, PK, NPK, and control. The chemical and microbiological soil properties and soil CO₂ emissions were monitored. The highest organic carbon content was observed under the NPK (1.42%) and NP (1.43%) treatments. N fertilizer application most significantly affected soil properties, including pH, electrical conductivity, and soil organic carbon content, altering the environment for soil microbial development and influencing the number and composition of soil microbial communities. On average, the field-measured soil C-CO₂ emissions were the most intensive under NP (2.76 kg ha⁻¹ h⁻¹), NPK (2.83 kg ha⁻¹ h⁻¹), and PK (2.51 kg ha⁻¹ day⁻¹) treatments.

Water erosion is the most important degradation process affecting Epicalcic Chernozems quality. Many technologies and tillage systems are used to control water erosion in agricultural areas and to preserve soil fertility. Cover crops are considered an agricultural practice that contributes to carbon sequestration, improved infiltration, erosion control, and improved microbiological processes. The aim of the present study was to determine how the continuous application of a cover crop, in a wheat-maize rotation on sloped arable land, would alter the soil organic carbon, greenhouse gas fluxes and the soil microbial community, as the most significant regulator of soil carbon dynamics and biogeochemical cycles. An experiment with wheat and maize, in rotation, with the application of up-and-down slope culture (T0), traditional contour tillage (T1) and crop specific erosion control contour tillage (T2) was performed for four years in the experimental field Trastenik, Ruse. The T2 variant includes minimum tillage, direct sowing and cover crop after wheat harvest and before maize sowing. The content of total organic carbon, labile organic matter, the number of main groups of soil microorganisms, as well as CO2 and N2O soil emissions were monitored. In comparison to T0 and T1 treatments, an increasing number of ammonifying, cellulose decomposers, actinomycetes, and nitrogen-fixing bacteria were determined in the T2 variant under maize. In the spring and summer, there were higher number actinomycetes and cellulose decomposers in wheat variants. The enhanced total organic carbon was determined in T2 treatments. Soil CO2 emissions (29.8 kg ha-1 day-1) were reduced in the minimum tilled wheat variant, followed by the T0 (30.0 kg ha-1 day-1) and T1 (30.8 kg ha-1 day-1). The soil crust formation due to more intensive erosion process explains the lower average emissions under maize at the T0 variant, grown conventionally up and down the slope in comparison with T1 and T2. N2O emissions were generally lowest in the T2 treatments for both crops in four years. The minimum tillage for maize and wheat growing on slope lands with the inclusion of cover crop in the rotation, have a positive effect on soil organic matter, microflora and GHG emissions.