Using thermal time models to predict seedling emergence of orchardgrass (<I>Dactylis glomerata</I> L.) under alternating temperature regimes

Abstract

The effects of alternating temperatures on seed dormancy changes, germination and seedling emergence were investigated in ‘Arctic’ and ‘Lineta’ orchardgrass (Dactylis glomerata L.). Thermal time models were successfully developed for 0, 5, 10 and 15°C temperature amplitudes, using 28 constant and alternating temperature regimes. These models were then modified by linking seed germination in Petri dishes and seedling emergence in soil. A field experiment was conducted with four seeding dates over 2 years to validate the modified thermal time models. Temperature regimes with a 5–15°C amplitude enhanced seed germination percentages of orchardgrass, indicating that the conditional dormancy was released by these temperature regimes. Base temperatures decreased with increasing temperature amplitude. Seeds germinated more rapidly under alternating temperatures than under constant temperatures. The dual effects of temperature for dormancy breaking and germination were accounted for by thermal time models based on alternating temperature regimes, which accurately predicted the timing and percentage of ‘Arctic’ and ‘Lineta’ orchardgrass seedlings emerging in the field (R2≥0.88).