Responses of soybean yield and yield components to light enrichment and planting density

Light intensity intercepted by the soybean canopy during the reproductive period is an important environmental factor determining soybean yield components and grain yield. A 2-year field experiment was conducted to investigate the effects of light enrichment and its interaction with planting density on yield formation of soybean cultivars. Light enrichment increased seed yield per plant and yield per unit area dramatically ranging from 26-94% (P<0.05) regardless of density and cultivars at lower and moderate density however the yield increase effect was not observed in H339 and HN35 at the high density in 2007. Seed yield and pod number per plant declined with the increased density in 2007 for all cultivars but remained unchanged in 2008 for KN18. There was significant light enrichment-by-density (P<0.05) on yield per plant and pod number per plant، but not on seed number per pod and seed size across the two years. Yield sensitivity to light enrichment differed among soybean cultivars. Adjustments to light enrichment imposed at the early flowering R1 stage increased pod number. Pod number per plant increased 20-119% over the two-years. Seed size in this study was unchanged or reduced slightly by light enrichment. Our data suggest that clarification of mechanisms induced the greatest yields in high population as demonstrated under light enriched conditions may provide insights for crop management and phenotypic improvement.