Tillage system effects on seedling recruitment pattern and persistance of lolium rigidum gaudin (annual ryegrass) seed-bank

Abstract

In the growing season of 2003, a field study was undertaken to investigate the effects of tillage systems on the vertical distribution, recruitment pattern and persistence of Lolium rigidum Gaudin (annual ryegrass) seed-bank. The tillage systems comprised low soil disturbance discs (Day-Break and K-Hart), intermediate narrow openers (16 mm Harrington knife point) and high disturbance Ribbon seeder (178 mm wide point). Assessment of vertical distribution of weed seeds after the sowing operation showed that in the case of the disc systems most (76%) of L. rigidum seed remained on the soil surface. In contrast, the surface seed-bank was considerably lower in the Harrington knife point (42%) and the Ribbon seeder (11%) systems. In the Ribbon seeder, about 80% of the seeds were found in the 1-5 cm soil layer, which is optimal seed placement for rapid germination. This difference between the tillage systems in the vertical distribution of seeds may have been responsible for the slower and lower final recruitment of L. rigidum seeds in the two disc systems. The persistence of L. rigidum seed however, was extremely high but unaffected by the tillage system. Irrespective of the tillage system, about 50% of L. rigidum seed carried-over from one growing season to the next, which is much greater than previously reported. The soil at this study site was non-wetting in nature and this may have been responsible for the unusually high persistence of the seed-bank of this species. Further research is needed to investigate the effects of non-wetting soils on the ecology and management of weed species.