The use of soil water by six grasses (perennial ryegrass, cocksfoot, timothy, rough stalked meadow grass (RSMG), tall fescue and Italian ryegrass) was measured over 2 years. The swards were cut either at 3-week (C 3 ) or 6-week (C 8 ) intervals. In both years the maximum soil water deficit attained under C 6 was greater than under C 3 . Following several of the cuts from C 6 there was a marked, although temporary, reduction in the rate of water uptake.An extended dry period in the second harvest year revealed substantial differences in the total water used and in the patterns of uptake from the soil profile by the grasses. Effective depths of utilization of water under treatment C 6 were: RSMG, 40 cm; timothy, 70 cm; cocksfoot, 70 cm; perennial ryegrass, 80 cm; tall fescue > 100 cm. This order of depth of utilization corresponded with the order of yields obtained during drought conditions. An examination of the root systems of four grasses also showed that, particularly under treatment C 6 , roots of tall fescue were more numerous at depth than those of timothy, cocksfoot or perennial ryegrass, and under this treatment it showed its greatest tolerance to dry conditions. Drought tolerance in these grasses appears largely determined by the volume of soil exploited by the roots for water.

The yield and quality of herbage produced by six grasses (perennial ryegrass, cocksfoot, timothy, rough-stalked meadow grass, tall fescue and Italian ryegrass) were examined both without irrigation and under two irrigation regimes. Water was applied according to the potential soil water deficit (potential SWD): the soil was either partially returned to field capacity (FC) after each cut or fully returned to FC whenever the potential SWD reached 25 mm. The swards were cut either at 3 (C 3 ) or 6 (C 6 ) week intervals over a 2 year period. Partial irrigation increased yields by 12-14 % in the first year and by 36-58 % in the second. Full irrigation produced little more growth than partial irrigation in the first year (maximum SWD, 188 mm) but increased yield by 78-93 % in the second, very dry, year (maximum SWD, 311 mm). Under treatment C 3 response per unit of water applied was similar with both partial and full irrigation, but under C 6 the response was greater with partial (2-86 kg D.M./m 3 ) than with full irrigation (1-79 kg D.M./m 3 ).There were marked differences between the species in their ability to grow under drought conditions in the second year of the experiment. Without irrigation, roughstalked meadow grass and Italian ryegrass did not survive the drought. The performance of tall fescue was markedly superior to both perennial ryegrass and cocksfoot in these conditions. Of the surviving grasses timothy made least growth.

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