Influence of environmental factors on the germination of barley grass ( Hordeum glaucum ) and annual ryegrass ( Lolium rigidum )

The ability of Hordeum glaucum to germinate and initially grow faster than Lolium rigidum was found to be influenced by the soil's physical state and its chemical characteristics. Glasshouse studies showed that the replacement of Lolium by Hordeum in undisturbed situations was due to the advantage of the latter having awned florets which anchor and lever the seed on smooth, compacted surfaces. Soil disturbance produces a broken surface upon which Hordeum has no advantage over Lolium. Hordeum is also able to germinate under higher osmotic pressures than is Lolium. Higher osmotic pressures will arise on stock camps and on alkaline soils where the salts are of biological and pedological origin respectively. Glasshouse and field observations showed that the top 3 mm of the soil surface are drier and more saline than the soil profile generally as indicated from measurements on soil cores. In undisturbed soil this surface layer will favour the dominance of Hordeum over Lolium. In cultivated soil the layer will be diluted throughout the depth of cultivation.