Effect of weather parameters on the date of emergence and the elapsed time to blooming of sunflower

Abstract

Changing of sowing time within the biological optimum has a direct effect (change of the length of the vegetation period) and indirect effect (spread of disease) on the yield. The yield quantity and quality of sunflower is affected by the length of the vegetation period, which is influenced by the sowing time and the weather of emergence date. Beard and Geng (1982) determined with principal component and path analysis that the hybrids with different phenotypes and genotypes react to the different sowing times similarly. In the case of an earlier sowing time than the optimal, the vegetation period of hybrids is shorter by 4-7 days, but in the case of a later sowing time, there is no difference during the vegetation period (Belevtsev et al., 1991). In the examinations of Bilteanu et al. (1986) there was a negative correlation between the number of day until emergence and the temperature of soil and air at sowing. The optimal sowing time was determined as between 15 March and 20 April under Romanian conditions. According to Encseva and Klocskov (1984), the earlier sowing time resulted in a 6-12 days earlier blooming compared to the optimal sowing date, also the ripening of the sunflower seed was faster in the case of an early sowing. Belevtsev et al. (1990) examined sunflower hybrids were sowed in 4-16 °C soil and experienced that the vegetation period increased by 3-6 days, but in the case of 10-12 °C soil the vegetation period was prolonged by 7-12 days.