Researchers studied how different seed sizes affect the grain yield of three wheat varieties over three years. They found that the size of the seeds had a significant impact on the yield, with the 2.5 mm and 2.2 mm seeds producing the highest yields. The variety of wheat also played a role, with Pobeda and PKB-Christina varieties yielding more than the Vizija variety. The highest overall yield was in 2005, with the 2.5 mm seeds producing the best results.