Base temperatures affect accuracy of growing degree day model to predict emergence of bermudagrasses

The germination of bermudagrass [Cynodon dactylon (L.) Pers.] under different temperature regimes has been extensively investigated, but a discrepancy remains between laboratory studies and field results. Thermal requirements calculated in growing degree days (GDD) have been found to differ within the same species depending on the location of the study. The accumulation of GDD may vary under different thermal conditions from seeding to seedling emergence and could depend on TBASE used in the calculation. The most widely used TBASE for bermudagrass is 5 °C. However, laboratory studies have suggested that a base temperature of 15 °C would more accurately predict seedling emergence. In this field study, we investigated the effect of using TBASE 5 °C vs. TBASE 15 °C on the estimation of GDD required by bermudagrass to emerge. Ten cultivars were seeded in northeastern Italy on three dates between 10 March and the end of April in 2013 and 2014. Number of emerged seedlings was counted weekly and soil temperature at 1-cm depth was recorded significant differences in seedling emergence between bermudagrass genotypes were found. Results demonstrated that the algorithm used to calculate GDD is strongly influenced by the TBASE used and to include a TBASE of 15 °C explains germination and emergence more accurately than a TBASE of 5 °C.