Effects of planting density on bulb yield in the tulip.
The effects of 5 planting densities (p), viz. 10x20, 10 x 10, 10 x 7. 5, 10 x 5 and 5 x 7. 5 cm., on leaf growth and bulb yield were investigated for 2 tulip cultivars. Leaf area per plant was nearly independent of p, so that apart from earlier senescence at high p with Apeldoorn and a slight reduction of plant leaf area at high p with Rose Copland leaf area index was directly proportional to p. Flower-stem length increased with increase in p. The reciprocal of the weight of bulbs lifted per bulb planted increased linearly with p, so that the bulb weight lifted per unit area was asymptotically related to p, giving peak bulb weight increases at 94 and 110 bulbs per sq.m. for Apeldoorn and Rose Copland, respectively. Bulb weight partition differed between the two cultivars, a higher percentage of bulb weight being found in the larger bulbs with Apeldoorn; this was partly due to the higher survival of small bulbs of Rose Copland. The numbers of forcing-size bulbs (11-cm. grade and above), expressed as a percentage of p, fell with increase in p. Forcing-size bulb numbers on a land area basis were highest at p values of 153 and 112 bulbs per sq.m. for Apeldoorn and Rose Copland, respectively. As p increased, mean bulb size fell. Expressing the change in bulb size spectrum in monetary value and including growing costs and costs of planting material provided data for a profitability analysis where p for maximum profit (£0.35 and £0.28 per sq.m.) was 65 and 45 bulbs per sq.m., respectively, for Apeldoorn and Rose Copland.-Glasshouse Crops Res. Inst., Littlehampton, and Kirton exp. Hort. Stat.