The researchers studied how planting density affects the growth and yield of Rehmannia glutinosa plants. They planted different densities of the plant and found that increasing density led to shorter plants and thinner tubers, but did not affect leaf size. Tuber yield increased by 40% at a density of 30 plants per row compared to 20 plants, and by 45% at a density of 40 plants. The best planting density for maximizing tuber yield and farmer income was determined to be 30 plants per row.