ENGLISH VERSION

ZESZYT 385

Sławomir Ligęza 
Variability of the contemporary Fluvisols of the Vistula River near Puławy
zeszyt 385, ss. 131

Fluvisols are soils that show high local variability of features, determined by parent material. Their properties depend on a river course, the position in a river valley, forms of floodplain use, and anthropogenic transformation. The purpose of this study was to analyse an impact of a soil depth, a distance from the river, and land use forms on the properties of alluvial soils.
The study was conducted on the floodplain located at the right bank of the Vistula River near Puławy. It is a genetically uniform geomorphologic landform structure. Different parts of the floodplain terrace are similarly elevated above the river level, and denivelations do not exceed 2 m. 
Six study sites with different land use forms were selected on the terrace: one arable field, two meadows, and three riparian forests. Depending on the width of the interembankment zone, one to five transects parallel to the Vistula River were established in each site, at distances of 0–25 m, 25–50 m, 50–75 m, and > 100 m from the river. 41 representative soil pits were dug within the transects/sites. Soil samples were collected from the depth of 0–150 cm: for the depth of 0–50 cm from five 10-cm layers while below 50 cm soils were sampled from the whole depth of C horizons. 
The following soil properties were analysed: Soil colour, macrostructure, specific gravity (ρ), bulk density (ρo), total porosity (Po), texture, pH in H2O and KCl, hydrolytic acidity (Hh), total sum of base cations (S), total content of cations (T = Hh + S), percent of alkaline cations (V), content of exchangeable Na, K, Ca, Mg, content of Corg and percent of its fraction (humus acids, hydrolysed and non-hydrolysed carbon), content of Nog, NNH4, NNO3, NNO3:NNH4 and C:N ratios, total phosphorus (Pog), iron (Feog), and aluminium (Alog). 
The profiles of studied alluvial soils have been stratified with lithic discontinuities. The number of discontinuities depended heavily on a distance from the Vistula River (with the highest numbers in profiles located at distances of 0–25 m and > 100 m) and on land use (with the most numerous discontinuities found in the riparian forests). The thickest humus horizons and the heaviest textured soils (silt loam) were observed at the Vistula bed and in the riparian forests. On the basis of the analyses, the soils were classified into two types: as Haplic Fluvisols (37 profiles) and Mollic Fluvisols (4 profiles). 
The mean values of specific gravity and bulk density were significantly lower and total porosity higher in the layer of 0–10 cm than in the others. The land use significantly influenced bulk density (ρo*: forests < grasslands, field) and total porosity (Po*: forests > grasslands, field) of the alluvial soils.
 The depth of soil and land use were important factors that diversified contents of Corg and Nog. The humus horizons contained more organic carbon and total nitrogen than the subsoil. All the sites were different in respect of Corg content (forests > grasslands > field), and the soils from the arable field had less Nog than those from the grasslands and the forests. The studied factors had little impact on the fractional composition of Corg. The share of carbon of humus acids in the total Corg was significantly lower in the riparian forest soils in comparison with those from arable field, while hydrolyzing carbon was higher for the grassland than the arable alluvial soils. Content of NNH4 depended mainly on the land form use (the highest in the riparian forests) and a distance from the Vistula bed (the highest in the transects of 0–50 m). The significant differences in content of NNO3 were related to the soil depth (the mean was higher in the layer of 0–10 cm than 20–50 cm), the distance from the river (lower content in the transect of 0–25 m than above 25 m), and the land use (higher content in the arable soils than in the grassland and forest soils). The values of C:N ratios were low and did not correlate with other soil properties. 
The soil reaction depended on the distance from the Vistula (with the least acid soils from the transects 0–50 m) and land use (with the most acid soils in the arable field). The mean values of Hh were significantly higher in the humus horizons than in the deeper layers, in the profiles located closer to the Vistula (0–75 m) than in those further away from the river (> 75 m), and in the grassland soils in comparison with the arable field. Alluvial soils developed in the transect at the distance of 0–25 m from the Vistula bed and in the forests had more alkaline cations than those located above 50 m away from the river, taken from the grasslands and the field. Exchangeable K content was significantly higher in the layer of 0–10 cm than below 20 cm, exchangeable Na was lower in the soils of the field in comparison with those sampled in the grasslands and the forests, all the sites differed in respect of exchangeable Ca concentration (forests > grasslands > field), and the content of exchangeable Mg was higher in the riparian forest soils than those from the grasslands and the arable field.
The land use was the most important factor of variability for the total phosphorus, iron, and aluminium. The soils from the forests contained significantly more Pog, Feog, and Alog than those from the arable field and the grasslands.
The present work allowed to explore changeability of the contemporary alluvial soils of the Vistula. The obtained results show that the form of land use is the most important factor influencing properties of Fluvisols. The distance from the river bed and the depth in the soil profile were less significant for the properties of the soils studied. The importance of individual factors should be taken into consideration at river valley and floodplain terraces management. Cutting down riparian forests changes the conditions of sedimentation and influences alluvial soils developed at river beds and the geomorphology of terraces. The discrepancy between the results obtained in the present study and those reported in other works shows the need for multifactorial analyses of the Vistual’s Fluvisols.