The assessment of the temperature below which plant growth ceases, known as base temperature (Tb) is key in for establishing the potential yield of a plant resource at a given location, and for quantifying the fitness of a given crop for a given production system. Whereas this is widely recognized, it is especially true in the case of perennial crops such as many of the forage species. This present study was aimed at developing, evaluating, and proposing a new methodological approach for the calculation of the Tb of forage crops, using both temperature and daylength, as a climatic variable named photothermal unit (PU). By using two regrowth cycles and their respective amounts of forage accumulated, the value of Tb can be calculated if the proportion between harvested yields and accumulated PUs of both regrowth cycles are the same. Yield data from two forage grass species, elephantgrass (Pennisetum purpureum Schum. cv. Napier) and Florico stargrass (Cynodon nlemfuënsis Vanderyst var. nlemfuënsis), from two field trials were used to test the proposed approach. Calculated Tb values were 15 and 12°C for elephantgrass and stargrass, respectively. These values are consistent with those generated by the classic method and reported in the literature.
pasture; growth; heat units; photothermal unit; degree-days
