the effects of planting date on quantitative and qualitative yield of sunflower in iran and the world: a meta–analysis

The science of meta-analysis provides a comprehensive summary of a set of researches whose results are more stable. meta-analysis study of the planting date effects on sunflower grain yield quality and quantity were very important in obtaining of perdition results and improving of the economical yield. in this study, using meta-analysis, we want to investigate the effects of planting date on grain yield (gy), number of seeds per head (ns/h) and head diameter (hd) using 40 articles published in iran and the world (between 1995 and 2018). according to the results, the correlation coefficient except for gy (r=0.2462), ns/h (r=0.2462) was not significant for hd trait. according to the table of average traits, the highest amount of gy (5173 kg. ha-1), ns/h (1818.35), hd (23.9 cm) was in basis of julian days (jd) with planting date 1-170 jd range. the highest gy in the range of sowing date 80-170 jd, the highest ns/h under 1-80 jd, the highest hd in 17-180 jd, the highest of grain oil percentage (gop) (52.16%) in 171-262 jd and the highest 1000-seed weight (tsw) (82.11 g) was observed in the treatment of 177-387 jd. according to the results of regression, except for tgw and gop, other traits showed a negative slope by changing the planting date. correlation coefficient was significant for gy (r=0.2462) and ns/h (r=0.364). based on the intensity model of the effect of sowing date on ns/h, gy and tsw under 1-80 jd, the sop in the range of 176-387 jd and hd in the range of 81-1701 jd were significant. according to the results of bias in the experiment based on funnel diagram, due to the large range of planting date, positive and negative effects of planting date on traits were observed. based on the accumulation diagram and review of each study, the general results of meta-analysis show it based on the accumulation diagram and review of each study, the general results of meta-analysis show that the best spring planting time identified under mid-may to mid-june (80-170 jd) and under subtropical to tropical regions from mid-february to mid-march (1-80 jd). in these 25 studies, considering the results of meta–regression no negative correlation was seen in the traits of the ns/h and gy. but for other traits no correlation was seen. on the other hand, the results of the accumulation chart also showed that the minimum and the maximum effect size were related to the studies that in addition to the cultivation date had studied the cultivar and cultivation methods including density. so, it is recommended that meta-analysis be done on the other factors.