Emergence and seedling structure of temperate grasses at different planting depths

Some producers have adopted ecologically based practices such as planting complex forage mixtures in their grazing systems to exploit the potential benefits of biodiversity. An understanding of grass seedling emergence and structure under different planting conditions could help develop planting recommendations for establishing multispecies swards. We conducted controlled-environment and field studies to compare the seedling emergence and morphology of several grasses at three planting depths. Perennial ryegrass (Lolium perenne L.; diploid and tetraploid cultivars), orchardgrass (Dactylis glomerata L.), prairiegrass (Bromus catharticus Vahl), and bromegrass (Bromus stamineus Desv.) were planted at 1, 3, and 6 cm in the growth chamber and greenhouse. Seedlings were destructively sampled 14 d after emergence, and leaves, tillers, and roots were counted. Mesocotyl length and coleoptile width were measured. The grasses were planted in two field experiments to determine emergence and seedling size when planted at 1, 3, or 6 cm. Both perennial ryegrass and orchardgrass elongated the mesocotyl from 1 to 4 cm depending on planting depth, but bromegrass and prairiegrass did not. Seedlings of bromegrass and prairiegrass had greater mass but fewer tillers and roots than perennial ryegrass. Increased planting depth reduced seedling size by reducing the number and size of leaves and number of tillers by 15 to 30% in all grasses. Differences in seedling size and structure among cultivars within species were positively correlated (r of 0.8 to 0.9, P < 0.05) with seed mass. Variation in seed mass and coleoptile width, however, did not explain differences among grasses in seedling emergence in the field.