The aim of the study was to compare the effect of conventional, simplified, and organic farming systems on changes in the content of soil organic carbon, organic matter fractions, total nitrogen, and the enzymatic activity. The research was conducted from 2016–2018 on arable land in the south-eastern part of Poland. The selected soils were cultivated in conventional tillage (C_Ts), simplified tillage (S_Ts), and organic farming (O_Fs) systems. The analyses were performed in soil from the soil surface layers (up to 25 cm depth) of the experimental plots. The highest mean contents of soil organic carbon, total nitrogen, and organic matter fractions were determined in soils subjected to the simplified tillage system throughout the experimental period. During the study period, organic carbon concentration on surface soil layers under simplified tillage systems was 31 and 127% higher than the soil under conventional tillage systems and organic farming systems, respectively. Also, the total nitrogen concentration in those soils was more than 40% and 120% higher than conventional tillage systems and organic farming systems, respectively. Moreover, these soils were characterised by a progressive decline in SOC and Nt resources over the study years. There was no significant effect of the analysed tillage systems on the C:N ratio. The tillage systems induced significant differences in the activity of the analysed soil enzymes, i.e., dehydrogenase (DH) and catalase (CAT). The highest DH activity throughout the experiment was recorded in the O_Fs soils, and the mean value of this parameter was in the range of 6.01–6.11 μmol TPF·kg⁻¹·h⁻¹. There were no significant differences in the CAT values between the variants of the experiment. The results confirm that, regardless of other treatments, such as the use of organic fertilisers, tillage has a negative impact on the content of SOC and organic matter fractions in the O_Fs system. All simplifications in tillage reducing the interference with the soil surface layer and the use of organic fertilisers contribute to improvement of soil properties and enhancement of biological activity, which helps to maintain its productivity and fertility.

The dynamics of litterfall and its quantitative differentiation in stands with different species composition suggest that the origin of the organic matter accumulated in the organic horizons of forest soils affects their physical properties, and thus, their ability to retain rainwater. The main aim of the study was to determine the physical properties, the degree of decomposition and capillary capacity of individual ectohumus sublevels of mountain forest soils, formed under fir stands (Abies alba Mill.) and beech stands (Fagus sylvatica L.), and to compare them with the physical and retention properties of the organic horizons of spruce stands [Picea abies (L.) H. Karst], as determined by Kucza (2007). The study was conducted on soil monoliths, sampled in a way that allowed preserving their natural structure. For individual ectohumus sublevels contained in the monoliths, the content and degree of decomposition of organic matter, bulk density, total porosity and capillary capacity were determined. It has been shown that the capillary capacity of the litter layer (Ol) differed significantly between beech, fir and spruce stands, assuming average values equal to 1.60 (±0.10), 2.76 (±0.11) and 4.44 (±0.10) mm H₂O in the layer of 1 cm, respectively. In the case of detritus (Ofh) horizons, the smallest water storage capacity characterized beech stands, wherein the capillary capacity was approximately 1.39 mm lower than in fir stands and over twice lower as compared to spruce stands.

As the outer layer of trees and shrubs, bark is exposed to the direct action of atmospheric conditions and reacts to changes in relative air humidity. This study focuses on the actual hygroscopicity of the bark, regarded as a component of the total bark retention capability. The main research aims were to: (1) determine the physical properties (specific density, bulk density, total porosity), actual hygroscopicity and maximum water storage capacity of the stem bark at breast height (1.3 m) of eight forest tree species; (2) assess the relationship between bark actual hygroscopicity and its physical properties; (3) determine the share of the actual hygroscopicity of bark in its maximum water storage capacity. Significant differences were observed among the different species considered as a consequence of the variation in physical properties of their bark. Actual hygroscopicity of bark (expressed in balance units), i.e., the maximum water amount that can be absorbed from saturated air by the outer bark layer, showed a significant relationship with bark physical properties. Depending on tree species, actual hygroscopicity may constitute from 10 to 30% of the maximum water storage capacity of bark.

Key message: Hygroscopicity is a crucial element of bark water storage and can reach >60% of water holding capacity of bark depending on tree species Bark forms the outer layer of woody plants, and it is directly exposed to wetting during rainfall and reacts to changes in relative humidity, i.e., it may exchange water with the atmosphere through absorption and desorption of water vapor. A current paradigm of bark hydrology suggests that the maximum water storage of bark empties between precipitation events and is principally controlled by bark thickness and roughness. We hypothesize that (1) the ability of bark to absorb water vapor during non-rainfall periods (i.e., hygroscopicity) leads to partial saturation of bark tissues during dry periods that may alter the rate of bark saturation during rainfall, and (2) the degree of bark saturation through hygroscopic water is a function of internal bark structure, including porosity and density, that varies among species. To address these questions, we conducted laboratory experiments to measure interspecific differences in bark physical structure as it relates to water storage mechanisms among common tree species (hickory (Caryaspp.), oak (Quercusspp.), sweetgum (Liquidambar styraciflua), and loblolly pine (Pinus taeda)) in the southeastern United States. Furthermore, we considered how these properties changed across total bark, outer bark, and inner bark. We found a distinct difference between hickory and oak, whereby hickory had 5.6% lower specific density, 31.1% higher bulk density, and 22.4% lower total porosity of outer bark resulting in higher hygroscopicity compared to oaks. For all species, hygroscopicity increased linearly with bulk density (R² = 0.65–0.81) and decreased linearly with total porosity (R² = 0.64–0.88). Overall, bark hygroscopicity may constitute an average of 30% of total bark water storage capacity. Therefore, in humid climates like those of the southeastern USA, the proportion of bark that remains saturated during non-storm conditions should not be considered negligible.