ha-1 applied 10 days after sowing) provided the best aster seedling survival. ha-1) applied pre-sowing did not significantly reduce aster emergence, while oryzalin (4.5 kg a.i. For direct sown aster, only trifluralin (2 kg a.i. ha-1 at 4 days after transplanting) provided excellent weed control and a tenfold increase in seed yield (to 568 kg ha-1). For transplanted aster, a single application of oryzalin (3.75 kg a.i. A series of experiments were conducted in 989 to evaluate herbicides which would provide good weed control without seed yield reduction, and which would not be phytotoxic to aster plants grown either as transplanted seedlings or when direct sown. Lodging and weeds were identified as constraints for seed production at this site and were studied in subsequent years. Both cultivars exhibited a high ability for compensatory reproductive growth. Kurenai and 4.9 to 44.7 plants m-2 in cv. Powderpuff at 17.4 plants m-2 (42 g m-2) but these yields did not differ significantly from those over a wide range of densities (between 12.7 to 44.7 plants m-2 in cv. Kurenai produced maximum seed yield at 27.8 plants m-2 (140 g m-2) and cv. Powderpuff respectively) before seed shedding started. Each seedhead needed 30 or 39 days from first opening for seed to reach physiological maturity and seeds could remain on the seedhead for a further 9 or 12 days (cv. A period of 18 days was required to complete flowering within each individual flower head, since florets opened sequentially from the outside ring through to the centre. The number of flower heads m-2 was the most important component determining final seed yield in both cultivars and was identified as an important plant characteristic to be manipulated for improving seed yield. Increasing plant densities increased branch numbers m-2 which led to increased leaf numbers, leaf area, plant dry matter and flowers and resulted in an increased number of potential seed production sites. Plant density effects on vegetative plant growth, flowering pattern, seed development, seed yield and yield components were investigated in 1987/1988 using a radial spacing design which provided plant densities ranging from 4.2 to 44.7 plants m-2. Abstract Seed production of two cultivars (Powderpuff and Kurenai) of China aster (Callistephus chinensis (L.) Nees.), grown under field conditions, was assessed to determine plant responses to the effects of plant density, crop manipulation by hand pinching and the application of three plant growth regulating chemicals, and some selected herbicides.
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