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.

Combined nitrogen CompetitionWhite clover KEY WORDS Root/shoot ratio Symbiotic nitrogen fixation SUMMARY Plants of white clover var. Blanca were grown singly in pots in controlled environments, or in small swards in a glasshouse, to determine how their distribution of dry weight between root and shoot was influenced when they were dependent on N2 fixation in their root nodules or when they lacked nodules but utilized an abundant supply of nitrate nitrogen. In single plants and in swards, changes in root/shoot ratio with increasing age and plant development were not influenced by the source of nitrogen, but nodulated plants always displayed a higher root/shoot ratio. When nodulated plants were supplied with nitrate nitrogen, root/shoot ratio declined to values intermediate between those of nodulated and of nitrate plants. The results are discussed in relation to the persistence of white clover, and the general level of productivity, in grass-clover swards.

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Plants of white clover (Trifolium repens L.) cv. Blanca and red clover (7". pratense L.) cv. Hungaropoly were grown singly in controlled environments. The effects of eight treatments on the two species were examined: 16-and 8-h photoperiods x 20/15 and 15/IO''C day/night temperalures X Rhizobium-hee plants receiving nitrate N and inoculated plants receiving no combined N. Twice weekly measurements ofthe main axis leaf size, petiole length, rate of leaf production and the time period between the appearance of a leaf and its final size were carried out for 8 weeks after sowing.Increasing the day/night temperature from 15/10 to20/15°C,ordoublingthedaylength from 8 to 16 h (doubling the daylength increased temperature by 16°C) accelerated the rate of leaf production and expansion and increased petiole length and the final area of leaves. Most aspects of main axi.s leaf growth were reduced in the inoculated plants dependent on their own N fixation compared with the noduIe-IYee plants receiving abundant nitrate N. The results suggest that the Icmperature above which white clover exhibits appreciable leaf growth in the Reid could be relatively high compared with grasses. Further research is required to define these differences and relate them to seasonal changes in the environment.

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