Response to inoculation and sowing date of soybean under Bafra Plain conditions in the northern region of Turkey

The Bafra Plain (latitude 410 35' N; longitude 350 56' E) which located surrounding of Kizil Irmak delta in the northern Turkey, has a short plant growing season for spring sowings. However, the soils of the region (about 80 000 ha) may have an important soybean [Glycin max (L.) Merr.] production potential with using the earliest or mid-earliest cultivars. Field experiments were conducted to determine the optimum sowing date of soybean, and effects of inoculation and sowing date on the yield and yield components. P-9292 soybean cultivar was evaluated either inoculated with Rhizobium japonicum or not inoculated at 3 sowing dates for 1991 and 1992 and 4 sowing dates for 1993 at Bafra, Samsun. The experimental design was a randomized block in a split plot with four replications. Both seed inoculation and early sowing increased seed yields for each year. With earliest sowings in 1991, 1992 and 1993 seed yields were obtained as 2728, 2786 and 2779 kg ha-1, respectively which were 969, 614 and 887 kg ha-1 more than the latest sowings. Duration of periods between VE-R1, R1-R3 and VE-R8 were found more closely related with high yields than nodule number, plant height and 100-seed weight. Early-May to mid-May was the optimum sowing period of soybean for Bafra Plain.