It was defined one of the most important questions of the study – the maintenance of hygroscopic waterfor Carex hirta L.plant (Hairy sedge) grownin oilpolluted soil.

Boryslav is an unique city where oil extraction is conducted directly on the city territory. This fact leads to a total contamination of soil by oil and its products that are highly toxic to plants and constitute a potential risk to human health. Just as recultivation of soil should be safe for the health of city population, so the most ecologic way of soil restoration is phytoremediation. It’s an effective technology which uses plants for cleaning up contaminated soil. C. hirta plants are resistant to oil contamination, and thus can be used for phytoremediation of oilpolluted soil.

For definitinon of nonavailablehygroscopic water contentit had been determinedthe field and laboratory researches. The experimental studies were conducted on the territory of Boryslav city.

Oil was added in soil in concentration 5%. C. hirta was planted in 20 days after the oil had spilt. In 30, 395 and 760 days of plant growth we selected soil samples from the rhizosphere and edaphosphere, that corresponded to 50, 415 and 780 daysof oildestruction. Hygroscopic water content was defined from the indicators of hygroscopicity, a hygroscopic coefficient and quantity of water in which the fading of plants began.

Sod-podzolic soil polluted by oil (5 %) had led to reduction of hygroscopicityindicators as well as hygroscopic coefficient.Especially these indicators were low in row-spacing. C. hirta growth in oil contaminated soil improved these indicators.

Calculation of plant nonavailable water content in oil polluted sod-podzolic soil has shown that in 50 days quantity of water in which the fading of plants began had incremented in the rhizosphere zone and rowspacing compared to background one. These indicators have a little decreased for 415 days of oil destruction. During the third year (780 day) quantity of water in which the fading of plants began had been less for background one.

The laboratory research with C. hirta plants has shown that they are capable to grow in drier soil. Practical indicators of permanent wilting point (PWP) were less both for background and oil polluted soil. However, the tendency of plant nonavailable water content remained: nonavailable water to C. hirta plants in oil-polluted soil had been more for background as well as in calculating. However, the difference in nonavailable water content between background and oil-polluted soil had been more than in calculating.

At the initial stage of oil destruction when quantity of oil in soil had still been high, water availability to C. hirta plants was very small. With increasing of oil destructionprocess the quantity of inaccessible water decreased. Most of nonavailable water has been for 415 days, when the plants were in the flowering phase.

Humidity range in conditions of C. hirta plants stasis has become higher in rhisosphere region and row-spacingcompared tothe background one in 50 days. In 415 days of oil destruction when C. hirta plants were in a phase of floweringthe indicator of late growth has increased much more compared to background one in rhisosphere region and row-spacing.

For the third year (780 days) in row-spacing where oil destruction happened more slowly than in rhisosphere region, the quantity of water inplant stasis has been higher compared to other years and rhisosphere region. For this period in soil there were heavy hydrocarbons of oil which were the most hydrophobic.

Thus, presence of oil in the soil leads to increasingplant nonavailable water content in which the plants are withering. C. hirta plant may be a good candidate for phytoremediation as itis capable to maintain lower indicators of humidity shortage than theoretically calculated one for the given type of soils. Growth of C. hirta plant improves soil hydraulic properties.

Key words: oil destruction,plant nonavailable water, hygroscopic water, permanent wilting point, oilpolluted soil, Carex hirta L.