Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2006
Publication Date: May 5, 2006
Citation: Bartholomew, P.W., Williams, R.D. 2006. Effects of exposure to below-freezing temperatures, soil moisture content and nitrogen application on phyllochron in cool-season grasses. Grass and Forage Science. 61:146-153. Interpretive Summary: Small livestock producers may have limited time available to make regular inspection of their cool season pasture and to determine its stage of growth. This makes it difficult to achieve optimum timing of management operations such as fertilizer application or harvesting. Accumulated average daily temperature data are widely available at the local level and may provide a good indicator of the state of forage development, without the need for close examination of the crop in the field. However, we do not know if accumulated temperature is a reliable indicator of grass development at times of the year when grass is exposed to temperatures below freezing. We examined the development of field-grown Italian ryegrass and found that in three successive years accumulated temperature maintained a consistent relation with grass development over the period January-March, even though plants were exposed to below-freezing temperatures. Experiments in controlled environments showed that the relation of accumulated temperature to grass development was influenced by soil type, by soil moisture, and by the number of times grass was exposed to below-freezing temperature. Adjustment for these factors will be necessary if accumulated temperature is used to predict growth of cool-season grasses.
Technical Abstract: Through its relation with leaf appearance interval, accumulated temperature may provide an indirect indicator of cool-season grass phenology that can assist farmers in timing of forage management operations. Field and controlled environment studies with Italian ryegrass (Lolium multiflorum Lam.) (IRG), tall fescue (Festuca arundinacea Schreb.) (TF) and tall wheatgrass (Elytrigia elongata (Host) Nevski) (TWG) measured leaf-appearance responses to accumulated temperature with varying conditions of low-temperature exposure, soil moisture and soil type. In controlled environment, reduced soil moisture content and more frequent exposure to below-freezing air temperature increased the interval between appearance of successive leaves (phyllochron) on the mainstem of IRG and TF. Phyllochron in IRG, TF and TWG was increased when seedlings were grown in field soil, rather than in potting soil. In field studies the phyllochron in IRG was consistent over 3 yr, at a mean of 182 growing degree days (GDD) leaf-1 during the months of January-March, but this was more than double the mean value measured in a controlled environment. During the early growing season accumulated temperature can be a consistent indicator of the development of IRG in the field. However, phyllochron may be modified by low-temperature exposure, limited soil moisture and soil type and further investigation of these effects on site-to-site variation in phyllochron is needed.