Dry-Matter Production by Field-Grown Tulips

Abstract

Periodic sampling of tulips of the cultivars Golden Harvest, Rose Copland and William Pitt provided data on growth patterns which were used in a growth analysis. An initial dry weight loss persisted until early April, by which time leaf area index had reached unity. This weight loss was identical in all three cultivars (0·016 gm. per gm. weight of bulb per week) and accounted for a third of the planting weight. The development of the leaf area index was slow, with indications of linear dependence upon soil temperature at bulb depth, between 5° and 10° C., but it fell rapidly from the peak value as the leaves senesced. At the standard planting distances employed, peak leaf area index values were between 1·7 and 2·4, depending upon cultivar, and leaf area duration was 18-25 weeks. Crop growth rates of between 8·3 and 9·5 tonnes per hectare were obtained; these figures are low because of the short period of active growth rather than because of low net assimilation rates. Partition of dry matter production between the parts is complicated by the initial falling-weight phase of growth. From the time of minimum plant weight, about 90% of dry matter production is taken up by the daughter bulbs. These findings are discussed in relation to data on other field crops and to possible means of increasing the efficiency of dry matter production.