COOL-SEASON GRASS DEVELOPMENT RESPONSE TO ACCUMULATED TEMPERATURE UNDER A RANGE OF TEMPERATURE REGIMES

Authors: Bartholomew, Paul; Williams, Robert

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2005
Publication Date: 4/1/2005
Citation: Bartholomew, P.W., Williams, R.D. 2005. Cool-season grass development response to accumulated temperature under a range of temperature regimes. Crop Science. 45:529-534.

Interpretive Summary: The productivity and longevity of pastures containing mixtures of warm and cool-season forages may be reduced by competition between them when both are actively growing in spring and fall. If farmers were able to predict the dates that grass growth starts they would be able to schedule pasture management operations to reduce harmful competition in mixed pastures. Accumulated average daily temperature is known to be closely related to grass leaf appearance and development, but we do not know whether the relation holds true when grasses are exposed to the day-to-day temperature variations typical of spring and fall. In experiments with seedlings of Italian ryegrass, tall fescue and tall wheatgrass we found that the interval between appearance of successive leaves, when expressed as the accumulated temperature requirement per leaf, was increased with higher average daily temperature. Leaf appearance interval also increased consistently when seedlings were exposed up to four times to night-time low temperatures of -5.0 or -7.5 C. The effects of variation in average daily temperature and of exposure to below-freezing temperature on rate of grass development need to be considered if accumulated temperature is used to predict the date that grass growth starts in the field.

Technical Abstract: Persistence and productivity of pastures containing mixtures of warm and cool-season forages may be compromised by interspecific competition when growing periods overlap. An ability to predict the onset and termination of growth of component species would facilitate timing of management interventions to minimize harmful competition in mixed pastures. Experiments were undertaken in controlled environment to assess the use of accumulated temperature values to indicate development stages in three cool-season grass species, and to evaluate the consistency of this relation under a range of temperature regimes that included variable exposure to below-freezing temperatures. When grown under light/dark temperatures regimes of 22.5/7.5, 17.5/12.5, 15.0/0.0, or 10.0/5.0 C, leaf appearance in Italian ryegrass, tall fescue and tall wheatgrass showed a close linear relationship with accumulated temperature, within each temperature regime. The interval between appearance of successive leaves on seedling mainstem (phyllochron), was increased by increased average daily temperature. In seedlings grown under a 15.0/0.0 C temperature regime, phyllochron was increased linearly by up to four 15-h exposures to -5.0 or -7.5 C dark-cycle temperatures in successive 24-hour periods. The effects of variation in mean daily temperature and of plant exposure to below-freezing temperature on phyllochron should be considered if accumulated temperature is used to predict development stage of cool season grasses in the field.