Seed of S24 perennial ryegrass of two weight ranges, 0.9–2.1 and 2.5–3.6 mg, were sown in soil at depths of 1.25, 2.5, 5.0 and 7.5 cm. Seedling growth was studied during the 3 weeks following germination.
Seeds of both weight ranges germinated equally well at soil depths down to 7.5 cm. However, the number of shoots that emerged was reduced as the sowing depth increased. At similar depths of sowing, seedlings from the heavy seed were heavier and developed more leaves and tillers than those from light seed. Deeper sowing reduced seedling weight and the rate of leaf- and tiller-production. After emergence, the relative growth rates of the seedlings which grew from seed of both weight ranges were similar at those depths of sowing which permitted the highest proportion of emerged shoots to seeds sown. This indicates that the weight advantage gained by the seedlings that developed from heavy seed during their non-photosynthetic stage of growth was maintained, and was not increased by a greater relative growth rate after photosynthesis began.
The implications of the findings are discussed in relation to plant breeding, commercial seed production and sward establishment.