Effect of Lodging on Seed Yield of Field-Grown Soybean-Artificial Lodging and Lodging Preventing Treatments

Three field experiments were conducted to elucidate the effect of lodging on seed yield of soybean (cv. 'Enrei'). In exp I, seeds were sown in mid-Jun for ten years (1999-2008) with a row width of 50-80 cm at the density of 10.0-12.5 plant m-2, and the effects of lodging score and climatic factors on seed yield were examined. The lodging score and climatic factors were not significantly correlated with seed yield in the experimental field. However, the number of typhoons that approached the area and the lodging score in the experimental field (except in 2001 damaged by phytophagous bugs) were closely correlated with the average yield in Okayama Prefecture, at 0.01 and 0.05 levels of significance, respectively. In exp II, the lodging-preventing treatment increased the yield; the medium level of lodging decreased the yield by 5-7%. In exp III, the artificial lodging at the flowering stage decreased the yield by only 9% due to the yield compensation by branch development, but that at the young pod to maturity stages decreased the yield as much as 34%, and that at the seed filling to maturity stages decreased it by 26%. It was concluded that the complete lodging at the seed maturation stage decreased the yield more than 30%, but the medium lodging at an earlier or later stage of reproduction decrease it by 5-15%.