Effect of sowing date on phenology and morphological traits of three grain sorghum (Sorghum bicolor L.) cultivars

order to study the effect of sowing date on phenology and morphological traits of three grain sorghum hybrids, an experiment was conducted during 2007 growing season at research field of Agriculture faculty, Tarbiat Modares University which is located in west of Tehran, Iran. Experimental treatments were arranged in split-plot layout based on randomized complete blocks with four replications. In this research sowing date inthree levels (8 June, 28 June and 18 July) were considered as main plots and grain sorghum cultivar in three levels (Payam, Sepideh and Kimia) were arranged in sub plots. Morphological traits, such as plant height, leaf area and panicle length were measured. Among Phonological traits, length of growth periods (vegetative period,initiation of 50 percent of panicle and physiological maturity) were investigated. Results showed that plant height in harvest time and panicle length was affected by sowing date (p≤0.05) and both of them obtained highest amount in 8 June sowing date. Also this sowing date had the longest vegetative period and also had the highest biological yield. Studies showed that panicle dry weight in this sowing date was taken highest level butnumber of seed production was lowest. Among cultivars, Sepideh had highest plant height and panicle length (p≤0.01). Also, Sepideh produced highest seed number.m-2 that explained its higher yield. Sorghum leaf area in flowering time was significantly affected by cultivar; in such manner Kimia had the highest LAI in this time,although Payam and Sepideh conserved more green leaf area until harvest time. Results also showed that the length of growth periods was affected by all factors. The highest vegetative period (45 days) was obtained in first sowing date (8 June) while longest period to physiological maturity was referred to third sowing date. Secondsowing date with suitable length of growing periods resulted to higher 1000 seeds weight, more seed number. m- 2 (number in square meter) and higher grain yield. Among cultivars, Sepideh had suitable length of growing periods and produced the highest grain yield (6777.2 kg.ha-1). So to produce higher grain yield in this region andsimilar places, sowing Sepideh cultivar in mid June is recommended.