Abstract
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).
Highlights
Soybean (Glycine max Merril) is one of the most important oil crops, has many applications in agriculture and industry; and in the past it was considered as one of the five sacred grains
In order to study the effects of plant density and planting date on new soybean lines, an experiment was conducted in the cropping year of 2010 in the research field of the Islamic Azad University of Qaemshahr, which has a latitude of 36 ̊72 ́, a longitude of 52 ̊46 ́ east, an altitude of 14.7 meters above sea level, and an average annual rainfall of 727.8 mm
As for the mutual effects of the cultivar, the plant density, and the planting date, the largest number of seeds per plant (94.7) was observed in the summer crop in line 033 at the density of D3 (20 plants.m2) (Figure 1), which can be attributed to the large number of pods per plant in that line
Summary
Soybean (Glycine max Merril) is one of the most important oil crops, has many applications in agriculture and industry; and in the past it was considered as one of the five sacred grains (wheat, millet, barley, rice and soybean). Choosing the suitable planting date is one of the cultural strategies agricultural producers can take advantage of to increase seed yield and the economic returns of planting soybean (De Bruin & Pedersen, 2008). Plant density is considered to be one of the main factors of production which greatly influences light absorption into the plant cover (Board, 2002). Ball et al (2000), Board et al (1990), and Norsworthy et al (2005) reported that the number of pods per plant and the number of seeds per plant compensated for low plant densities. Jason and Emerson (2005) announced that low plant densities in soybean may result in an increase in the number of lateral branches and in a greater contribution of these lateral branches to the total yield. Singh et al (2000) carried out research on 7 soybean cultivars at densities of 100 to 600 hundred thousand plants per hectare and concluded that the density of 400000 plants per hectare performed better than those of less than and similar to 600000 plants per hectare. Ball et al (2000), Board et al (1990), and Norsworthy et al (2005) reported that the number of pods per plant and the number of seeds per plant compensated for low plant densities. Jason and Emerson (2005) announced that low plant densities in soybean may result in an increase in the number of lateral branches and in a greater contribution of these lateral branches to the total yield. Vasilia et al (2005) reported that oil and protein contents www.ccsenet.org/ijb
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