Field experiments were conducted at the Agronomy field laboratory (24°75' N, 90°50' E, Altitude 18 m), Bangladesh Agricultural University (BAU), Mymensingh during Rabi (dry and cool) 2004-05 and 2005-06 and kharif II (rainy and warm) 2005 seasons. The experimental area belongs to the Sonatola Soil Series under the Old Brahmaputra Floodplain Agro-ecological Zone (AEZ 9) with Non-calcareous Dark Grey Floodplain soil (UNDP/FAO, 1988). The soil was loam in texture having pH 6.84. The soil contained low organic matter (1.50%), total nitrogen (0.073%), phosphorus (12.0 ppm), sulphur (9.5 ppm), zinc (0.47 ppm) and medium amount of potassium (0.18%). The soil test result also showed that the amount of P, K, S and Zn were relatively higher in Kharif-II season than those in Rabi seasons while the amount of total nitrogen was higher in Rabi season than in Kharif-II season. Two soybean varieties viz., Bangladesh soybean-4 (G-2) and Shohag (PB-1) and six planting densities viz., 20, 40, 60, 80, 100 and 120 plants m-2 were included in the trial with a split plot design having variety been assigned into main plot and plant density into the subplots with three replications. The trial was conducted during three consecutive seasons such as rabi 2004-05, kharif 2005 and rabi 2005-06 growing seasons in the same plot with same trial design. Unit plot size was 4.4x3.0 m. Seed was sown after inoculation with Rhizobium inoculum on 6 January, 28 July and 3 December 2005 respectively for rabi 2004-05, kharif 2005 and rabi 2005-06 growing seasons. An equidistant square planting pattern having spacing 22.4x22.4 cm; 15.8x15.8 cm; 12.9x12.9 cm; 11.2x11.2 cm; 10x10 cm and 9.1x9.1 cm, respectively were used to create target plant densities of 20, 40, 60, 80, 100 and 120 plants m-2 as per experimental specification. The experimental fields were opened on 26 December 2004 for Rabi 2004-05 season, on 20 July 2005 for Kharif-II 2005 season and 25 November 2005 for Rabi 2005-06 season. In both the Rabi seasons, a tractor drawn disc plough followed by harrowing with a power tiller were used to prepare a good seed bed while in Kharif-II season land preparation was done with a power tiller. Each unit plot was uniformly fertilized during final land preparation at 23-69-60-16-1 kg ha-1 N-P2O5-K2O-S-Zn through urea, triple super phosphate, muriate of potash, gypsum and zinc sulphate (BARI, 2005). Sowing was done on 6 January, 28 July and 3 December 2005, respectively for rabi 2004-05, kharif 2005 and rabi 2005-06 growing seasons. Three seeds were sown per hill at 2-3 cm depth. Prior to sowing seed was inoculated with Rhizobium inoculums collected from Bangladesh Institute of Nuclear Agriculture (BINA). Different intercultural operations such as weeding, thinning, gap filling and irrigation were done as and when needed. For example, weeding was done at 20 and 40 DAS in Rabi 2004-05, 20 and 30 DAS in Kharif-II 2005 and 21, 34 and 50 DAS in Rabi 2005-06 seasons followed by thinning to maintain a single seedling at each hill as per experimental specification. Gap filling was done at 42 DAS in Rabi 2004-05 and 35 DAS in Rabi 2005-06 seasons with the additional seedlings of same age raised in a corner of the experimental field and the irrigation was applied at the same day. In Kharif-II 2005 season, gap filling was done twice, first at 30 DAS and second at 37 DAS. In Rabi 2005-06 season, second irrigation was given at 65 DAS because the soil moisture deficit of a plot reached about 50% of the field capacity. The crop was infested by hairy caterpillar in all the three seasons. The rate of infestation was higher in Kharif-II season than Rabi seasons. The hairy caterpillar was successfully controlled with the application of Dimethion 40 EC at 1.5 Lha-1 at 65 DAS in Rabi 2004-05, 28, 44 and 56 DAS in Kharif-II 2005 and 61 DAS in Rabi 2005-06 seasons. There was no disease infection in the crop field. The crop was harvested at full maturity from the central 6.36 m2 area (2.52x2.52 m) of each plot. In Rabi 2004-05, both the varieties were harvested on 20 April 2005, in Kharif-II 2005, variety G-2 and PB-1 were harvested on 27 October and 14 November 2005, respectively while in Rabi 2005-06, harvesting was done on 1 and 9 April 2006 respectively for variety G-2 and PB-1. After threshing, cleaning and drying the weight of seed of each plot was recorded at dry weight basis and seeds were kept in air tight polythene bags at 8% seed moisture content in the laboratory until further use. The analysis of N, P, K, Ca, S and Zn content in soybean seed was done at the Central Laboratory, BAU, Mymensingh, Bangladesh. Seed samples were oven dried at 65°C for 48 h, then were finely grounded using a Wiley Mill and homogenous powder was obtained for analysis purpose after passing through a 60-mesh sieve. The total N in the seed was determined by Semi-micro Kjeldahl method and P was determined by spectrophotometer. K was determined by flame photometry while Ca Zn and S were estimated by an Atomic Absorption Spectrophotometer (AAS). The experimental data were analyzed using two way-Analysis of Variance (ANOVA) techniques and mean differences were adjudged by Duncan’s Multiple Range Test with the help of a computer package programme MASTAT-C. The correlation and regression analyzes were done using statistical package program MINITAB.