effect of sowing date and sulfur on yield, oil content and grain nitrogen of safflower (carthamus tinctorius l.) in autumn cultivation

introduction nowadays oilseed crops are considered as the second most important sources of energy in the diet. in this regard, cultivation of oilseed crops such as safflower (carthamus tinctorius l.) is important due to quality of oil seed and medicinal properties. different planting dates leads to adaptation of vegetative and reproductive growth of plant to temperature, day-length and various solar radiations and as a result affects plant’s development phase and yield. with delayed planting date , temperature and day length increases and development phase will accelerate. in this condition the crop yield will reduce due to crop growth and developmental period will shorten. sulfur is an essential element for plant nutrition and its role is greater than phosphorus. using sulfur increases the heads per plant and grain yield. in order to investigate the effect of sulfur fertilizer under heat stress condition at the terminal growth stages and its role in reducing the negative effects of high temperature stress on safflower, this research was performed. materials and methods in order to study effect of planting date and sulfur manure on yield components, nitrogen and oil percent in safflower, a field experiment was carried out in a randomized complete blocks design with three replications in as split plot arrangement at ramin agriculture and natural resources university of khuzestan during 2013-2014. the experimental treatments consisted of four planting dates of 30 november, 21 december, 22 january and 1st february were randomly placed in main plots and four levels of sulfur of 0, 200, 400 and 600 kg ha-1 performed randomly in subplots, sulfur fertilizer was corporated to soil one week before each planting date. harvest was performed from the mid-may to early-june, during physiological maturity. to measure the yield on maturity time after the removal of margins, safflower plants were harvested from one m2 unit area. nitrogen percent was determined by kjeltec analyzer unit device. grain oil was measured by porim procedure and finally the oil yield was calculated by multiplying oil content and the grain yield. data from the experiment was analyzed using sas software and mean comparison was carried out using lsd test at the 5% of probability. results and discussion planting dates significantly affected grain number per head, biological yield, oil yield, grain yield, heads per plant and grain nitrogen. sulfur fertilizer had a significant effect on grain number per head, oil yield, grain yield, heads per plant and grain nitrogen. there was a significant interaction between planting date and sulfur on grain yield, number of heads in plant and grain oil percentage. the late planting date resulted in plants exposed to high temperature and resulted in decreased safflower yield and yield components. based on the results, the highest grain yield 4012.66 kg.ha-1 obtained in planting date 21 december. late planting dates reduced grain yield to 50.28 percent. it was concluded that 200 kg.ha-1 sulfur increased grain yield through increasing the grain number per head and the number of heads in plant. delayed planting decreased growth period length and resulted in reduced yield and its components. but the application of sulfur fertilizer by increasing yield components can compensate the loss of yield. sulfur is sub-structure of fatty acid metabolism enzymes in fatty acid and bond formation reactions for the production of oil and involved in fat acids. planting date and sulfur application in appropriate form increased grain and oil yield. shortening the growing season due to a delay in planting and plant distance from the right conditions for growth reduced the grain yield. these factors limited the plant grow in optimal conditions, disrupted synthesis of primary and secondary metabolites in plants and had a negative effect on seed oil percent. conclusions delay in planting date reduced, flowering, grain filling period, potential production and economic performance. delay in planting date reduced yield, dry matter production and harvest index. sulfur increased photosynthesis and affected the formation of protein and fatty acids, which increased oil and nitrogen percent and grain yield. the study showed that late planting date reduced seed yield and oil performance, but using the 200 kg.ha-1 of sulfur from organic granular sources increased yield and yield components.