Investigation on phenology of Bromus tomentellus using growing degree-day method

In agriculture، growing degree day accumulation is commonly used to predict crop development، classify species and hybrids as to maturity data and evaluate climate for crop suitability، but relationships between degree day accumulation and phonological development of range species have received less attention. This research tested the hypothesis that phenological development is related to degree day accumulation and that these relationships are stable over environment. Therefore this study was conducted in two different field studies on Bromus tomentellus. One of the most important steps in the design of degree-day system is establishment of the base temperature. For this purpose، seed plants are grown in a controlled environment، at constant temperature (10، 15، 20، and 25 ۫ºC) and constant photoperiod، with development rate expressed as a function of temperature. The best fitting line of development rate versus temperature is extrapolated to zero growth. The point at which this line crosses the temperature axis defines the best temperature. Thresholds (base temperature) are different for each species. The linear regression analysis showed highly significant (p=0. 01) between rate development and temperature for this species. Degree day can be easily calculated by using the average daily temperature minus the base temperature. Degree day are totaled over a period of days to determine when a plant has reached a certain phonological stage. Based on the species and condition of this study، plant phenological stages can be predicted from accumulated growing degree-day. Determining relationship between plant phenological development and management، especially in determining grazing readiness، and in refinement of growth and management simulation models.