INFLUENCE OF PLANT POPULATION ON YIELD PERFORMANCE OF TWO SOYBEAN VARIETIES UNDER RAINFED CONDITIONS IN SUDAN

Field experiments were carried out at Damazeen, Central Sudan (11 45' N) on a clay soil (organic matter 1.62% and pH 7.0) during 1985 and 1986 seasons. The total amount of rainfall during the two growing seasons (June-October) were 732 and 912 mm, respectively. The effect of various seeding rates (180, 240, 300, 360, 420 and 480 thousand viable seeds/ha) on seed yield and other agronomic character­istics of Doko and Tropical soybean varieties were studied. Seeding rate did not affect days from planting to 50% flowering or maturity. Mean­while, it affected significantly plant height and lowest pod height, in the two growing varieties. Increasing seeding rate significantly decreased all yield components, except 100-seed weight, but considerably increased seed yield and lodging of both varieties. Increasing seed rate from 180 to 240, 300, 360, 420 and 480 thousand viable seeds/ha significantly increased seed yield by 23, 86, 73, S7 and 39%, respectively in Doko variety and 22, 54, 83, 66 and 41%, respectively in Tropical variety. Optimum seeding rate was 300,000 or 360,000 viable seeds/ha for Doko variety and 360,000 and/or 420,000 for Tropical soybean variety.