EFFECT OF SOWING TIME ON THE OIL CONTENT OF DIFFERENT SUNFLOWER HYBRIDS

Introduction The production of numerous hybrids with different adaptability, and improving the effectiveness of the sunflower production makes it reasonable to develop hybrid-specific technologies in the case of sunflower. In the range of the biological optimum changing the sowing time has a significant effect on the development of yields. It influences the growth of plant by changing directly the length of the vegetation period, this way influencing the quantity and quality of the crop, and indirectly affecting the extent of disease infections. The favorable effect of early sowing was observed by Harper and Ferguson (1979). According to them the early sowing has a positive effect on the crop and oil content. In sowing time experiments started from mid-March, sowing in May caused significant loss of yield and quality in Proda's et al. (1985) Romanian experiments. Late (July) sowing produced small yield based on experiments conducted in the central areas of the USA. The early sowing supported higher oleic acid, while late sowing favored high linol acid content (Owen, 1983). According to Encseva (1984) the quantity of crop and the oil yield decreased as a result of postponing the sowing time. The overdue sowing in May caused considerable loss of yield in the experiments of Er and isik in Turkey (1988). The oil content was higher in the early sowing time (50 %), while it decreased to average 47 % in the later sowing time. The panicle and its oil content were the highest in the earliest sowing time (20 April) in the researches of Kotecki and Malarz in Poland. In the sowing time experiments performed in the interval of 4 to 16 °C of soil temperature, different soil temperatures did not have a significant effect on the height of plants, diameter of the plate and the oil content, but the significantly highest yield was produced on 10 to 12 °C soil temperature (Belevtsev et al., 1990). By sowing in March, April and May Goksoy et al. (1998) found that the yield decreased as a result of postponing the time of sowing similarly to the weight of thousand panicles, panicle weight by plates, oil content and oil yield.