Influence of environmental factors on seed germination and seedling emergence of rigid ryegrass (Lolium rigidum)

Rigid ryegrass is a major weed of southern Australian cropping systems. Increased knowledge about the germination biology of rigid ryegrass would facilitate development of effective weed control programs. The influence of different environmental factors on seed germination of rigid ryegrass was studied. The level of seed dormancy in five different populations, collected from different fields on the same farm, was found to be similar, suggesting consistency in seed dormancy in populations at a single location. Dormancy release was more rapid for seeds after-ripened in the field compared with those after-ripened dry in a greenhouse. Seed decay was found to be an important contributor to the loss of seeds for this species from the seed bank in the field. Seed decay was much greater for seeds after-ripened on the soil surface compared with buried seed. In contrast, germination played an important role in the loss of buried seed as compared with surface seed. Regardless of the burial depth, the dormant seed component present at the end of the growing season was quite small (4 to 16%). Seedling emergence of rigid ryegrass in the field was greater (49%) for seeds buried at 1 cm than for those on the soil surface (16%). No seedlings emerged from seeds buried at 10 cm. Seed germination of rigid ryegrass was tolerant to a wide range of PH and showed some tolerance to salt and osmotic stress. The results indicate rigid ryegrass is unlikely to become a greater weed problem in notill compared with cultivated seeding systems.