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The present study was conducted to evaluate the yield and agronomic traits of commercial soybean genotypes and introduce the genotypes that are compatible with higher yield potential for both spring and summer cultivation seasons. This study was carried out in a split plot experiment based on randomized complete blocks with three replications during two cropping years, 2008-2009 and 2009-2010, in the field of agricultural and natural resources research center of Moghan. The main plot was the cultivation date in two levels of summer and spring cultivation and the subplot was 14 cultivars of soybean including Sahar, Linford, Hobbit × Williams, Davis× Williams, 032, DPX, Ronack, JK, BP, 033, Clarck,Williams, Zan and L17. A combined analysis of the grain yield over two years revealed that the effect of cultivation date, genotype and their interaction was significant at 1% probability level. Comparison of the two cultivation dates demonstrated the yield rates of 3642.1 and 2530.3 kg/ha for spring and summer cultivation, respectively. Zan and Linford varieties with yield rates of 4276 and 4105 kg/ha respectively over the spring cultivation and the cultivar of BP and L17 with yield rates of 2974 and 2920 kg/ha respectively over the summer cultivation had the highest yield among all cultivars.

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Studyign of soybean cultivars under abiotic stress conditions to improve their yield is important. This experiment was carried out as a strip plot based on a randomized complete block design with three replications in the Safiabad Argicultural Research Center. Vertical factor consisted of foure levels of irrigation (Irrigation after 50, 90, 130 and 170 mm evaporation from class A pan) and horizontal factor was 6 soybean genotypes (504, Katoul, Safiabadi, BP×Safiabadi, Migmat and Salend). Results showed that the effect of drought stress, genotypes and their interactions were significant on grain yield. The mean comparison of drought stress × genotype interaction showed that the highest grain yield (4522 Kg ha-1) achieved in irrigation after 50 mm evaporation from class A pan in Migmat and the lowest grain yield (1017 Kg ha-1) belonged to Katoul genotype with irrigation after 170 mm evaporation from class A pan. Pod number per plant decreased by 16%, 28% and 51% with increasing irrigation intervals to 90, 130 and 170 mm compared to irrigation after 50 mm evaporation. The treatments did not have any significant effect on the number of grain per pod. It is concluded that, irrigation after 50 mm evaporation from class A pan would be suitable for Migmat and BP×Safiabadi genotypes. Irrigation after 90 mm evaporation from class A pan appropriate for 504, Salend, Katoul and Safiabadi genotypes.

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In order to determine the appropriate sowing dates, seed rates and their interaction effects on yield and yield components, oil and protein contents of soybean variety Sari, a split-plot experiment based on a randomized complete blocks design with four replications was carried out at Qaemshahr Gharakeil Agriculture Research Station in 2009. Five sowing dates including 15^th May, 31^th May, 15^th June, 1^th July and 16^th July were considered as main plots and three different seed rates including 60, 75 and 90 kg ha^-1 as the sub-plots. The results showed that all of yield components were affected by sowing dates and also seed rates had a significant effect on the number of pods per plant. Although due to increasing seed rates, yield components, such as pods per plant were decreased, but because of the increasing number of plants per square meters, seed yield not decreased significantly. Therefore for economically saving 60 kg ha^-1 of seed rates will be preferred. In this study high mean value of seed yield, biological yield and 1000-seed weight was achieved in first sowing date and all of the yield component characters were decreased in late sowing dates. Harvest index was increased in late sowing dates and it was not significantly affected by seed rates. Sowing dates and seed rates had not significant effects on oil and protein percentages, but due to significant effects of sowing dates on seed yield, oil and protein yields were significantly affected by sowing dates. In this study higher seed yield was belonged 60 kg ha^-1 of seed rate in first and second sowing dates which have not significant statistically differed.