Investigation of the Effects of Plant Density and Planting Date on the Quantitative and Qualitative Yields of Two Advanced Soybean Lines

A split split plot experiment in the format of randomized complete block design with three replications was carried out in the experimental field of the Islamic Azad University of Qaemshahr in 2010. The treatments included the planting dates (28th April and 14th June) as the main plot, the soybean lines 032 and 033 as the sub plot, and the plant density (20, 28 and 40 plants per square meter) as the sub-sub plot. Results obtained showed that the plant density was only significant concerning the features of the number of seeds and the number of pods per plant, the planting date was also only significant regarding the harvest index, the percentage seed oil content was also just influenced by the cultivar used and by the mutual effects of the planting date and the cultivar and also by the mutual effects of the planting date and the cultivar. The summer crop was superior to the spring crop in all the features studied, because it seemed that the high temperature and the very little rainfall before and after pollination and flowering reduced seed and pod formation in the spring crop, as compared to the summer crop. In most of the features studied, line 033 performed better than line 032. Moreover, the most desirable density for obtaining the highest seed and oil yield was 20 plants per square meter, because at this density features such as the number of seeds per plant, the number of pods per plant, the 100-seed weight, and seed oil content were superior. Soybean planted after harvesting wheat (i.e. the summer crop) exhibited greater potential regarding seed yield as compared to the crop planted after harvesting canola (i.e. the spring crop).