Yield-density relation of glyphosate-resistant soya beans and their responses to light enrichment in north-eastern USA

Optimum plant population densities are a key means of achieving higher seed yield in soya bean [Glycine max (L.) Merr.]. Limited information is available on yield-density relation of glyphosate-resistant soya beans in north-eastern USA. The objective of this research was to determine the appropriate populations for glyphosate-resistant soya beans, and if the yield potential of glyphosate-resistant soya bean produced in light-enriched conditions was affected by populations. Eight glyphosate-resistant soya bean cultivars with three populations (300 000, 500 000 and 800 000 plants ha -1 ) were grown under both ambient and light-enriched conditions in 2002 and 2003. Yield of all cultivars responded to density linearly. As density increased, grain yield was increased by up to 92 % among cultivars. Light enrichment increased yield for all cultivars across the 2 years, although some cultivars were more sensitive. Harvest index either remained unchanged or declined slightly at higher density in 2002, and there was no difference among treatments in 2003. Both pod number and seed number per plant were significantly decreased with the increase of density across the 2 years, while seeds per pod declined slightly or remained unchanged. Greater seed size was obtained in higher density with varied degree depending on cultivars across the 2 years except for those cultivars with relatively larger seed. The increase in seed size by light enrichment was cultivar and density dependent, and varied between years. 800 000 plants ha -1 could be a suitable practice in producing higher yield in north-east USA for glyphosate-resistant soya bean. Maintaining the mass of an individual seed is an important strategy in achieving high yield at high population. Establishing mechanisms responsible for the greatest yields via high population under light-enriched conditions, may provide insights for management and phenotypic improvement.