ENGLISH VERSION

ZESZYT 353

Jacek Pranagal 
The physical state of selected silty soils of on the Lublin Region

Introduction and objectives. Cultivation involves numerous agrotechnical practices with the use of various tools or machines that may have a different effect on soil. Proper soil conditions are determined by a set of physical, physicochemical, chemical, and biological properties. Relationships between these properties have a decisive influence on soil quality. Studies on soil environment focusing on physical properties have been scarce in Poland. It should be stressed that improvement of chemical soil qualities with no change in unfavourable water and/or air properties is insufficient to have a beneficial effect on pedosphere. Among physical properties influencing soil quality, the most frequently mentioned are soil structure and aggregate stability, bulk density and total porosity, penetration resistance and water-air properties. The purpose of this study was to determine a direction of changes in soil structure and its physical properties in terms of quantity and quality. The physical state of the soil studied was assessed on the basis of threshold limit values and qualitative classifications. 
Material and methods. The study was conducted in areas representative of various land-use forms: large commercial monocultures such as orchards and hop gardens, arable fields, and permanent grasslands. Old forest ecosystems were used as control plots. In this study, soils developed from silt, i.e. Chernozems, Luvisols, and Fluvisols, collected from Lublin Upland and Wołyń Upland, were analyzed. The following soil properties were determined: morphology of pedons, colour, texture, morphology and morphometry of the soil structure, aggregation and water stability, bulk density and total porosity, air-water properties and physical soil quality.
Results. Long-term agricultural land use had no effect on diversity in the soil morphology of the sites investigated. The only exception were the forest soils where a different sequence of surface genetic horizons was observed. The analyses of soil structure showed that long-term land use was reflected in its morphology and values of morphometric parameters, the ability to form aggregates and their stability. The most favourable structure, characterized by good porosity and aggregation, and with a substantial portion of structural elements formed by soil biota, was found in the forest plots. In the soils taken from the arable field and the hop garden in particular, agricultural use led to considerable deterioration, disappearance of zones with aggregate structure replaced with strongly compacted zones with a massive structure. At the same time, a structure with no strongly compacted zones was observed in the orchard soils. A structure of the grassland soils was mostly beneficial for plants, which was similar to that of the forest soils. To sum up, maintenance of the grassland seemed to provide the most favourable conditions for soil aggregation, while the hop plantation was the least favourable in this respect. Among the soils studied, Fluvisols offered the best environment for the formation of aggregates, in contrast to limited opportunities found in Luvisols developed from loess. Deterioration of soil structure had a clear adverse effect on water-air conditions and compaction in the soils studied.
Discussion. The results obtained led to the conclusion that the soil-aggregate water-stability index WT can be used as a sensitive indicator of soil physical quality. Therefore, based on WT values, the aggregates were classified according to their stability as follows: very unstable < 15%; unstable 15–35%; moderately stable 35–60%; stable 60–95%; and very stable > 95%. The classification of soil physical quality proposed by Dexter and Czyż [2007] and based on the values of S index should be adjusted as it results mainly from water properties. According to this classification, the silty soils studied were categorized in most cases (81.7%) as very good even though their air properties tended to be not particularly good. Instead, the validity of the following classification based on S index could be tested: very poor < 0.020; poor 0.020–0.035; limitary or transitional 0.035–0.050; good 0.050–0.070; and very good > 0.070. On the basis of linear regression analysis, threshold limit values were calculated for selected physical properties that may be used for preliminary evaluation of the physical state of soil. For maintenance of proper water-air conditions in soil, values for some physical properties should be as follows: RWU > 0.140 kg·kg-1; RWP > 110 kg·kg-1; PO > 0.435 m3·m-3; MZ > 0.215 m3·m-3; and ς < 1.48 Mg·m-3. 

Conclusions. Deterioration of structure in the soils from the hop garden and arable field resulted in their considerably impaired abilities to retain water as well as impeded airflow and soil solution. The total volume of macropores (> 20 μm), mainly that of the group > 300 μm, turned out to be one of the physical properties showing the highest sensitivity to change. The findings about very good quality of soil structure and other properties defining a physical state observed in soils under grassland should be used in agricultural practice. Namely, mechanical cultivation should be suspended every several years. Besides, grasses alone or combined with papilionaceous plants should be introduced to arable fields as a factor contributing to substantial improvement in soil physical status. In hop plantations, the utilisation of grass stripes on a permanent basis is recommended, and old hop gardens requiring regeneration should also be left uncultivated periodically.