Seed size has received special attention by researchers, who have studied aspects related to seed performance and the resulting plant. The objectives of this study were to evaluate the effects of seed size on initial plant growth, grain yield and the physiological seed quality of soybeans by testing seeds of three cultivars (BRSMG 752S, BRSMG 790A and BRSMG 750SRR), graded into three sizes (4.0 mm, 5.0 mm and 6.0 mm). No-till planting was done on December 6th, 2007 and the plants thinned 21 days after emergence to 13 plants per meter. Harvesting and seed threshing were done manually on April 11th, 2008. After harvesting, seeds were manually graded into three sizes by using round perforation screens of 6.0 mm, 6.5 mm and 7.0 mm. The field trials were set up in a completely randomized block design and the laboratory analyses followed a completely randomized design, both having a factorial of 3 cultivars x 3 seed sizes and four replicates. Data were submitted to analysis of variance by the F test and means were compared by the Tukey test at the 5% probability level. The analyzed field parameters were plant height and grain yield (kg.ha-1 at 13% moisture) and the laboratory parameters measured were seed germination and vigor, measured by accelerated ageing, classification of seed vigor, seedling length and tests for seedling dry mass. Small seeds (4.0 mm) resulted in shorter plants at harvest with a lower grain yield potential when compared to large seeds (6.0 mm). Physiological seed quality varied among the different sizes of the harvested seeds: best performance was observed with large seeds (7.0 mm) for the three cultivars. The effect of seed size on vigor was significant since large seeds (7.0 mm) had the highest vigor.
Glycine max; screen; viability; vigor
