The effects of bitumen mulch and sowing date on the establishment and yield of oil-seed sunflower (Helianthus annuus L.)

Experiments in 1976 and 1977, in southeast Scotland, with sunflower (cv. Fransol) examined the effects of bitumen mulch applied after sowing, date and depth of sowing on emergence, flowering and yield. Bitumen mulch increased soil temperatures in April and May by 1-4-5 -C resulting in earlier emergence (6-7 days), more complete emergence under adverse conditions of early and deep sowing, and earlier flowering (2-5 days). Delaying sowing from 7 April to 5 May reduced emergence time and time from sowing to first anthesis. Larger seedlings, having an increased leaf area, resulted from bitumen mulching and early sowing. In the laboratory, increasing temperatures from 5 to 20 -C reduced the average germination time by 0-75 days for each increase of 5 -C. Germination percentage was not affected by temperature over this range. Average seed yields and oil content were markedly different in 1976 and 1977; 2-22 t/ha and 44-7 for 1976 and 0-95 t/ha and 36-9 for 1977. Bitumen mulch and sowing depth had no effect on seed yield or oil content but delaying sowing until 5 May reduced both. Lower seed yields in 1977 resulted from fewer and smaller seeds. Infection of the seed heads with grey mould (Botrytis cinerea) after flowering was high in both years.