A double-cropping system with soybean (Glycine max) following the cultivation of potato, garlic, and onion is widely adopted in the southern region of Korea. For this system, marginal dates for planting must be determined for profitable soybean yields, because the decision to plant soybean as a second crop is occasionally delayed by harvest of the first crop and weather conditions. In order to investigate the effect of planting date on soybean yield, three cultivars (early and late maturity) were planted on seven different dates from May 1 to July 30 in both paddy and upland fields across 2012 and 2013. Soybean yields were significantly different among the planting dates and the cultivars; however, the interaction between cultivar and planting date was not significant. Based on linear regression, the maximum yield of soybean was reached with a June 10 planting date, with a sharp decline in yield for crops planted after this date. The results of this study were consistent with those of a previous one that recommends early and mid-June as the optimum planting period. Regardless of soybean ecotype, a reduction in yield of greater than 20% occurred when soybean was planted after mid-July. Frost during soybean growth can reduce yields, and the late maturity cultivars planted on July 30 were damaged by frost before completing maturation and harvest; however, early maturity cultivars were safely harvested. For sufficient time to develop and reach profitable yields, the planting of soybean before mid-July is recommended.

Materials and Methods
  Preparation of plant materials
  Analysis of seed constituents
  Statistics
 Results
  Soybean growth and yield components
  Soybean growth period and yield
  Variations in compositions of seeds planted atearly and late dates
 Discussion
  Sowing date and soybean yield
  Sowing date and seed composition
  Marginal sowing date in the southern region ofKorea
 Summary
 RERERENCES

• Hyeon Jin Park(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA) Corresponding author
• Won-Young Han(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)
• Ki-Won Oh(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)
• Sang-Ouk Shin(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)
• Byong Won Lee(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)
• Jong-Min Ko(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)
• In Youl Baek(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)
• Hang Won Kang(Crop Production Technology Research Division, Department of Southern Area, NICS, RDA)