MATERIALS AND METHODS

This investigation was conducted at the experimental farm of Sakha Research Station, Kafr El-Sheikh, during 2010 and 2011 summer growing seasons. The objective of this investigation was aimed to study response of soybean genotypes i.e., Giza 21, Giza 22, Giza 111, H₂L₁₂, H₃₀ and H₃₂ to different sowing dates 20th April, 5^th May, of 20^th May and 5^th June on growth, seed, oil and protein yields/ha. The experimental design was conducted in Randomized Complete Block Design (RCBD) with four replications. Four separate experiments in each seasons in 20th April, 5^th May, 20^th May and 5^th June was done and then combined analysis was conducted between sowing dates to obtain the main effect of planting dates and the interaction between cultivars and planting dates. Each plot consisted of four ridges, 60 cm apart and four m long. Seeds of all genotypes were inoculated by specific Rhizobia and then hand planted at density of 15 plants per a meter of a linear ridge on the sowing dates. All other recommended agricultural practices were conducted for Sakha region.

The data of Crop Growth Rate (CGR), relative growth rate (RGR) and net assimilation rate (NAR) were measured according to (Radford, 1967). Leaf Area Index (LAI) was measured according to Watson (1952). Data of seed yield/ha was determined from the central area (4.2 m²) in each plot, then transformed to ton/ha and seed protein and oil content were determined according to (AOAC, 1980) then multiplied with seed yield/ha to obtained protein and oil yields in kg ha^-1.

Statistical analysis: All collected data were subjected to statistical analysis of variance as described by Sendcor and Cochran (1967). Combined analysis of sowing dates experiments to obtain the mean effects of sowing dates and their interaction with cultivars according to Waller and Duncan (1969). The mean values were compared according to Duncan’s Multiple Range Test (Duncan, 1955).

RESULTS AND DISCUSSION

Soybean genotypes in all planting dates were significantly differed in seed, oil and protein yields/ha as well as growth parameters, indicating the extended of genetic diversity in the material selection for this study (Table 1, 2). Significant means due to the interaction between genotypes and planting dates were obtained for all the studied traits. These results therefore, might reveal the performance of genotypes differed from one planting date to another. Seed, oil and protein yields/ha as will as growth parameters were differed between cultivars and planting dates in both seasons. The results in Table 1 clearly indicated that highest CGR and NAR values (187.04, 199.22 and 48.35, 50.60) in both seasons, respectively was obtained from planting on 5^th June. In addition, highest RGR and LAI values (0.24, 0.23 and 3.51, 3.67) in both seasons, respectively was produced from planting on 5^th May. Moreover, sown H30 line produced highest values of CGR, NAR and LAI, which were 209.22, 230.1 and 54.22, 59.49 and 3.26, 3.52 in both seasons, respectively. Delaying planting dates decreased yields, with greater reductions measured for Giza 21 cultivar in both seasons. Others have noted genotypes by planting date interaction (Beaver and Cooper, 1982).

Table 1:	Means of vegetative growth parameters as affected by genotypes and planting dates during 2010 and 2011 seasons
*, ** and NS indicate p<0.05 and not significant, respectively Means designated by the same letter within columns are not significantly different at the 5% level according to Duncan's multiple range test

Table 2:	Means of 100 seed weight, seed, protein and oil yields /ha as affected by genotypes and planting dates during 2010 and 2011 seasons
*,**and NS indicate p<0.05 and not significant, respectively, Means designated by the same letter within columns are not significantly different at the 5% level according to Duncan's multiple range test

There were significant effects for planting dates and genotypes. The effect of planting date and cultivar on yield components and growth characteristics were significant in each year (Table 2), indicated that planting date on 5^th June significantly produced highest values of crop growth rate and net assimilation rate in both seasons. Planting on 5^th May gave the lowest values of crop growth rate in both seasons. The lowest net assimilation rate values were produced from sowing on 20^th April. The results clearly showed that highest values of crop growth rate and net assimilation rate were obtained from late planting than those of early planting, which could be attributed to short of the stature of late planting of soybean and then decrease in crop duration, especially the vegetative growth period and the fast transfer to reproductive stage and maturity (De Bruin and Pedersen, 2009). The results indicated that planting on 5th May significantly produced highest values of relative growth rate and leaf area index in both seasons. Whereas, the lowest rate was obtained from planting on 20^th May of relative growth rate and leaf area index in both seasons. For a given planting date, vegetative production by H30 line at all studied characters were consistently the greater among studied genotypes, although the difference was quite small for Giza 21 cultivar, however, the lowest rate gave by H₂ L₁₂ line. Similar conclusions were reported by Abd-Alla and Omran (2002), Pedersen and Lauer (2004), Mehasen and Saeed (2005), De Bruin and Pedersen (2009) and Shairef et al. (2010).

Table 2 clearly showed aaveraged across planting date, highest seed yield/ha and oil yield/ha was obtained from planting on the first May only (5059.88, 5331.2, 1003.99 and 1055.16 t ha^-1) in both seasons, respectively. Weight of 100-seed was obtained from 20^th planting (15.87, 16.19 g, respectively) and sown on 20^th May produced highest protein yields (1640.00 and 1811.74 kg ha^-1). Results in Table 2 clearly showed that Giza 21 cultivar recorded highest 100-seed weight, seed yield (t ha^-1) and oil yield (kg ha^-1) which were, 17.28, 17.28 and 4936, 5164.6 and 952.29, 987.91 in both seasons, respectively. In addition, H2L21 genotype produced highest protein yield/ha which were 1710.61 and 1566.13 t ha^-1 in both seasons, respectively. Whereas, H32 line recorded the lowest values, except H30 line and Giza 22 cultivar with protein yield (kg ha^-1), in the first and second seasons, respectively. Such increases in seed yield may be attributed to the considerable increases in leaf area index and 100-seed weight. Consequently, increases in oil and protein yields/ha may be due to increases in seed yield/ha or oil and protein percentages. Similar conclusions were reported by Bastidas et al. (2008), El-Borai et al. (2008), Egli and Cornelius (2009), De Bruin and Pedersen (2009) and Shairef et al. (2010).

There were a significant effects due to the interaction between genotypes and planting dates, results in Table 3 clearly showed that H30 line recorded highest growth values with the latest planting date (5^th June) on crop growth rate and net assimilation rate, whereas, highest values recorded with the second planting date (5^th May) with respect to relative growth rate and leaf area index. However, lowest values of crop growth rate, relative growth rate and net assimilation rate were obtained from planting H₂ L₁₂ line on 5th June. H32 line recorded the lowest values of leaf area index.

Table 3:	Means of vegetative growth parameters as affected by the interaction between soybean genotypes and planting dates in 2010 and 2011 seasons
**and NS indicate p<0.01 and not significant, respectively, Means designated by the same letter within columns are not significantly different at the 5% level according to Duncan's multiple range test

Table 4:	Means of 100-seed weight, seed, protein and oil yields/ha as affected by the interaction between soybean genotypes and planting dates in 2010 and 2011 seasons
**and NS indicate p<0.01 and not significant, respectively, Means designated by the same letter within columns are not significantly different at the 5% level according to Duncan's multiple range test

The results in Table 4 clearly showed that planting Giza 21 cultivar on 5^th May recorded highest of 100-seed weight, seed yield (t ha^-1) and oil yield (kg ha^-1).Whereas, planting Giza 21 cultivar on 5^th May gave the highest protein yield/ha. Planting Giza 111 cultivar on 20^th May gave highest protein yield/ha. Planting H30 line on 5^th June produced the lowest 100-seed weight. Planting H32 line on 20^th April gave the lowest seed yield/ha and planting Giza 22 cultivar on 5^th June gave the lowest protein and oil yields/ha. High temperature during reproductive stages of R5 and R6 enhanced oil content and generally reductions of protein content (Dornbos and Mullen, 1992) Similar results were reported by Hassan et al. (2002), Hamed (2003), Mehasen and Saeed (2005) and De Bruin and Pedersen (2009).

CONCLUSION

It could be summarized that planting Giza 21 cultivar early on 5^th May maximized seed, oil and protein yields/ha of soybean under the environmental condition of Kafr El-Sheikh District, Egypt.