Plant density affects soybean seed quality

The effects of plant density on seed quality of two cool-tolerant soybean cultivars were examined in two consecutive seasons at the same site in Canterbury, New Zealand. In the first season (2000/2001), 25 plant densities ranging from 2 to 84 plants/m(2) were established using a systematic (radial) trial design, while in the second season (2001/2002) 5 plant densities (from 16 to 74 plants/m(2)) were established in conventional replicated plots. Plant density had no effect on germination in either season, but seed vigour, as assessed by accelerated ageing (both seasons) and conductivity (first season) was reduced as plant density increased. Thousand seed weight also decreased as plant density increased and this is a possible explanation for the vigour loss. The plant populations which produced the greatest seed yield (40 plants/m(2) or higher) produced lower quality seed than plant populations below 40 plants/m(2).