Two series of pot experiments were conducted in 2004 in the greenhouse of the University of Warmia and Mazury in Olsztyn. Meadow fescue (cultivars Skra and Skawa) and timothy (cultivars Kaba and Karta) were grown at the optimum level of soil moisture (80% of field water capacity) and at moisture deficiency (40% of field water capacity).  Soil moisture content was differentiated after emergence. In order to maintain the appropriate soil moisture, water losses were made up on a daily basis, to achieve a specified weight of the pot with soil. Kick-Braukmann pots were filled with 8 kg peat-muck soil containing 29.7% organic matter. The available nutrient content of the soil was as follows: 320 mg P, 540 mg K and 300 mg Mg, and 5 mg Cu, 28.6 mg Zn, 88.6 mg Mn and 112.6 mg Fe·kg^-1 soil. Soil reaction in 1 n KCl was pH 4.9.  During the growing season, the rate of photosynthesis was determined with a LI-COR 6400 portable gas analyzer and leaf greenness was measured with a SPAD 502 chlorophyll meter (Minolta). The plants were cut down three times. The concentrations of total protein, crude fiber, ash, phosphorus, potassium, calcium and magnesium were determined in the biomass. It was found that water deficit reduced photosynthesis rate by 44%, on average. The meadow fescue cultivar Skawa showed the strongest response to moisture deficiency, manifested by a decrease in photosyntesis rate reaching 47%. SPAD values, representing the chlorophyll content of leaves, increased in all cultivars grown under water deficit conditions. Chlorophyll concentration was significantly higher in meadow fescue plants (by approx. 14 SPAD units, on average) than in timothy plants. The drop in soil moisture from 80% to 40% caused a decrease in dry matter yield. Of the investigated cultivars, the highest yield decrease was reported for the timothy cultivar Karta, while the lowest – for the meadow fescue cultivar Skawa. All cultivars grown under soil moisture deficiency conditions contained more total protein and calcium and less crude fiber and phosphorus, compared with control treatment plants. No significant changes were observed with respect to the levels of crude ash, potassium and magnesium. The results of the study indicate that the meadow fescue cultivar Skawa was the most resistant to water deficiency in soil. Despite a considerable decrease in the rate of photosynthesis, the yield of this cultivar dropped only slightly under water deficit conditions.

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