The objective of this study was to investigate the influence of water stress conditioning on the photosynthesis response of switchgrass (Panicum virgatum L.) and tall fescue (Festuca arundinacea Schreb.) to moisture deficiency. Tillers of the two species were grown in the same, controlled, environment and were subjected to three conditioning water stress cycles, or were kept well watered. After drought conditioning all plants were subjected to moisture deficiency while photosynthesis and leaf water potential were monitored. Measurements were taken between –0.8 and –4.0 MPa and the rate of water stress was 0.49 MPa/day. The conditioning of switchgrass produced a 26% reduction in the photosynthesis rate during drought, while that of tall fescue produced a 57% reduction in photosynthesis. Both species maintained elongation and photosynthesis down to lower leaf water potentials after drought conditioning than before conditioning. The conditioning water stress cycles decreased the leaf conductance, mesophyll resistance and transpiration of tall fescue plants after rewatering. The leaf water potential of conditioned switchgrass plants was lower upon rewatering after three conditioning water stress cycles than the leaf water potential of non-conditioned plants, while the leaf conductance, mesophyll resistance and transpiration of conditioned and non-conditioned tillers were equal. These data indicate an improvement in the drought tolerance of tall fescue and switchgrass plants, emphasize the importance of knowing the previous water stress history of the plants in moisture deficiency experiments, and help to choose proper irrigation management for switchgrass and tall fescue.
L.) biomass, which is of a good quality in the middle of summer, when cool-season grasses are unproductive, is a very important source of forage. This study measured the influence of the date of first harvest and cutting height on the first and regrowth yields of switchgrass cultivars Blackwell and Cave in Rock. The experiment was conducted in Blacksburg, VA, USA on a Groseclose-Poplimento soil to determine the influence of four dates of harvest and two cutting heights on the yield of switchgrass in 1990, and the influence of the treatments in previous years on the yields in 1991 and 1992. The first yield of both cultivars increased as the date of first harvest was delayed and the cutting height reduced. The regrowth yield of both cultivars declined as the date of first harvest was delayed. A shorter cutting height caused reductions in vigour and yield potential in the second year, whilst in the third year the harvested yield was only 40–50% of that obtained from previously unharvested stands.