الفهرس 
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Abstract
Field experiments are conducted at the Experimental Farm of Agricultural Research Station, Sakha, Kafr El-Sheikh, Egypt, during 2010 and 2011 seasons. The field experiment was aimed to study the effect of four different sowing dates and six soybean cultivars on vegetative growth, yield and yield components and seed quality of soybean plants. The experimental design four experiments in each season were conducted in randomized complete block design (RCBD) with four replications. Each experiment included six cultivars as follows Giza 21, Giza 22, Giza 111, H2L12, H30 and H32. Combined analysis was done between the four sowing dates to measure the mean effect of sowing dates and interaction between cultivars and sowing dates i.e. 20th April, 5th May, 20th May, 5th June.
Crop growth rate (CGR), relative growth rate (RGR) and net assimilation rate (NAR) shows significant difference among the examined four sowing dates at the time of vegetative growth period in both seasons. The highest (CGR) and (NAR) values were recorded by sowing on 5th June in both seasons.
The results indicated that highest relative growth rate (RGR) was produced from sown on 20thApril and 5th May significantly which exceeded other sowing dates in this trait.
Leaf area index and number of branches per plant increased significantly due sowing dates. Soybean sown on 5th May produced highest values of leaf area index and highest number of branches per plant in both seasons.
The results showed that highest total chlorophyll content of soybean leaves was produced from sown on 5th June and significantly exceeded other sowing dates in this trait.
The results showed that number of days to maturity significantly affected by sowing dates. Sowing on 5th June significantly recorded earliness number of days to maturity in both seasons.
Plant height (cm) and stem diameter (cm) significantly differed due to sowing dates. Sowing soybean on 20th May significantly produced the tallest plants in both seasons.
It could be recommended that soybean cultivar Giza21 or Giza111 should be sown on 5th May for maximizing seed yield and its seed quality under Kafr-Elsheikh Governorate conditions.