Cool-Season Grass Development Response to Accumulated Temperature under a Range of Temperature Regimes

tion in temperatures. Accumulated temperature (growing degree days, GDD) is related to crop growth and develPersistence and productivity of pastures containing mixtures of opment in cereals and grasses (Moore and Moser, 1995; warm and cool-season forages may be compromised by interspecific competition when growing periods overlap. An ability to predict the Mitchell et al., 1997) and to the interval between appearonset and termination of growth of component species would facilitate ance of successive leaves (phyllochron) in wheat (Trititiming of management interventions to minimize harmful competition cum aestivum L.), barley (Hordeum vulgare L.), and forin mixed pastures. Experiments were undertaken in controlled enviage grasses (Cao and Moss, 1989; Frank and Bauer, ronment to assess the use of accumulated temperature values to indi1995; Kirby, 1995; Skinner and Nelson, 1995). Accumucate development stages in three cool-season grass species, and to lated temperature values have been proposed as a means evaluate the consistency of this relation under a range of temperature to predict harvest date and time of nitrogen application regimes that included variable exposure to below-freezing tempera(Kowalenko et al., 1989) and for prediction of crop tures. When grown under light and dark temperature regimes of 22.5 emergence in a warmand coolseason grass mixture and 7.5, 17.5 and 12.5, 15.0 and 0.0, or 10.0 and 5.0 C, respectively, (Fidanza et al., 1996). Lemaire and Salette (1982) releaf appearance in Italian ryegrass (Lolium multiflorum Lam.), tall fescue (Festuca arundinacea Schreb), and tall wheatgrass [Elytrigia ported that spring vegetative growth of tall fescue and elongata (Host) Nevski] showed a close linear relationship with accucocksfoot (Dactylis glomerata L.) was related to accumulated temperature, within each temperature regime. The interval mulated temperature and suggested that this relationbetween appearance of successive leaves on seedling mainstem (phylship could be used to predict spring growth. Accumulochron) was increased by increased average daily temperature. In lated temperature values may be a more useful tool for seedlings grown under a 15.0 and 0.0 C temperature regime, phylloprediction of onset or termination of growth than a sinchron was increased linearly by up to four 15-h exposures to 5.0 or gle threshold temperature because they integrate day7.5 C dark-cycle temperatures in successive 24-h periods. The effects to-day temperature variation through use of short-term of variation in mean daily temperature and of plant exposure to belowhistoric (within cropping cycle) data. By convention, freezing temperature on phyllochron should be considered if accumulated temperature is used to predict development stage of cool-season GDD accumulation for cool-season grasses and cereals grasses in the field. is calculated as the accumulation above a mean daily temperature of 0 C and this may be justified by observations that leaf growth in many temperate forage species T need to reduce costs of livestock feeding has continues down to 0 C (Peacock, 1975a, 1975b, 1976; created interest in extending the grazing season and Parsons and Robson, 1980). However, at air temperahas resulted in increased use of cool-season forages in tures associated with late fall and early spring, GDD areas of the southern Great Plains (SGP) that have traaccumulations above 0 C may be associated with a beditionally depended primarily on warm-season forage low-zero minimum temperature. The impact of diurnal for livestock feed. However, in mixed pasture systems temperature change on plant development and on reinterspecific competition during transitions between sponse to accumulated temperature is not clear, particuwarm and cool-season cropping may limit productivity larly when plants are exposed to temperature minima or reduce persistence of some pasture components. Efthat are at, or below, the limits to growth. The objectives fective management of the transition from warm-season of the work reported here were to determine whether to cool-season production and vice versa depends, in part, the relation between accumulated temperature and leaf on determining the developmental stage of component appearance in cool-season grasses remains constant species in the pasture and when they begin and termiover a range of temperature regimes characteristic of nate growth. Although temperature threshold data are early and late growing season, and when plants are exfrequently used to determine the beginning and end of posed to temperatures close to or below 0 C. a growing season, average temperatures provide only an approximation of the actual dates at which crop growth MATERIALS AND METHODS starts and stops (Broad and Hough, 1993) and do not account for the effects on forage growth of day-to-day variaPlant Materials and Growing Environment Individual seedlings of Italian ryegrass cv. Marshall (IRG), USDA-ARS, P.O. Box 1730, Langston Univ., Langston, OK 73050. tall fescue cv. Kentucky 31 (endophyte-infected) (TF), or tall Mention of trademark names does not represent an endorsement over wheatgrass cv. Jose (TWG) were used in all experiments. any other products by the USDA-ARS. Received 15 Mar. 2004. Crop For all experiments, seedlings were grown in 155 mL “ConeEcology, Management & Quality. *Corresponding author (PBarthol@ tainers” (Stuewe & Sons, Corvallis, OR) in Baccto potting luresext.edu). soil (Michigan Peat Co., Houston TX), consisting of 900 g kg 1 reed sedge peat 100 g kg 1 perlite and sand, as the Published in Crop Sci. 45:529–534 (2005). growing medium. Plants were maintained in a growth chamber © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA (Controlled Environments Inc., Pembina, ND) in a 13-h light 529 Published online January 31, 2005