Abstract
The study was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during Rabi 2004-05, Kharif-II 2005 and Rabi 2005-06 seasons with the objective of examining the effect of field environment manipulation on growth, seed yield and quality of soybean. Five experiments were carried out where sowing date, plant density, row spacing, irrigation and seasons were used to create variation in field environment in the same location. Three soybean cultivars viz.; Bangladesh Soybean-4 (G-2), Shohag (PB-1) and BARI soybean-5 (BS-5) were used in the study. The five experiments included in the study were: (1) Effect of sowing date on growth, seed yield and quality of soybean, (2) Effect of plant density on growth, seed yield and quality of soybean, (3) Effect of irrigation and row spacing on growth, seed yield and quality of soybean, (4) Effect of row spacing and cultivar on growth, seed yield and quality of soybean, and (5) Effect of sowing date and row spacing on growth, seed yield and quality of soybean. Experiment 1 was conducted in Rabi 2004-05 and Kharif-II 2005 seasons where six sowing dates viz.; 4 and 24 November, 14 December, 3 and 23 January and 12 February and two cultivars viz. G-2 and BS-5 were included in the first season while four sowing dates e.g.; 25 July, 14 August, 3 and 23 September, and the three cultivars were included in the later season. Experiment 2 was conducted in all the three seasons with six plant densities viz. 20, 40, 60, 80, 100 and 120 plants m⁻², and two cultivars viz. G-2 and PB-1. Experiment 3 included three row spacings such as 20, 30 and 40 cm and two irrigation levels viz. full irrigation and no irrigation along with two cultivars viz. G-2 and BS-5 in Rabi 2004-05 and cultivar G-2 and PB-1 in Rabi 2005-06 season. Experiment 4 was conducted only in Kharif-II 2005 season with four row spacings viz. 20, 30, 40 and 50 cm and all the three cultivars. Experiment 5 contained four sowing dates viz. 26 November, 16 December, 5 and 25 January, three row spacings viz. 20, 30 and 40 cm and both G-2 and PB-1 cultivars. The result revealed that Rabi season crop gave higher seed yield than Kharif-II season crop. Cultivar G-2 gave higher yield in Rabi season while cultivar PB-1 and BS-5 produced higher yield in Kharif-II season. Cultivar G-2 and PB-1 produced higher yield at 20-30 rows corresponding to plant density of 80 to 100 plants m⁻². The yield improvement in soybean for sowing date was attributed to improvement in number of fertile pods plant⁻¹, seeds pod⁻¹ and weight of 100-seeds while for plant density and row spacing treatment due to all the characters except weight of 100-seeds. Optimum sowing date of cultivar G-2 ranged between early November to mid December and that for cultivar PB-1 ranged between mid December and early January in Rabi season. Cultivar BS-5 and PB-1 can give high yield for sowing during the last week of July in Kharif-II season. Soybean produced the highest dry matter at R5 stage and the dry matter accumulation was strongly related to growing degree days indicating that seed yield can be estimated from air temperatures. Seed yield and number of seeds unit⁻¹ area was linearly related to the photothermal quotient (PQ). The crop that produced high seed yield also produced seed with high germination and vigour. Seed protein content did not show any relation with seed germination and vigour. Seed protein content had negative relationship with seed phosphorous, potassium, calcium, sulphur and zinc content. Thus the field environment that favours high seed yield could be considered for producing high quality seed. The present study suggests that sowing of suitable cultivars in optimum dates at 20 cm row in irrigated condition can produce higher soybean seed yield with good quality.