Abstract
We evaluated the appropriate planting density in ridge-making narrow-row cultivation of two soybean cultivars “Enrei” and “Ayakogane” in drained paddy fields with heavy clay soil in Niigata prefecture. Two cultivars differed in their adaptability to dense planting cultivation. The relative photosynthetically active radiation (PAR) under the plant canopy with narrow row cultivation decreased with increase in the planting density. The relative PAR at any planting density was less than 10% at the flowering stage, which was sufficient to suppress weed growth. Higher planting density led to more spindly growth at the maturing stage in both cultivars. The lodging index of “Enrei” in narrow row cultivation with the planting density over 17.8 plants m–2 was higher than that in conventional cultivation with 75 cm interrow space and 8.9 plants m–2. The lodging index of “Ayakogane” in narrow-row did not differ from that in conventional cultivations. The seed yield of both cultivars tended to increase with increasing planting density. The seed yield of “Enrei” cultivated at a planting density over 17.8 plants m–2 was significantly higher than that under conventional cultivation. The yield of “Ayakogane” was also increased at a planting density over 13.3 plants m–2. The appropriate planting density to avoid lodging in ridge-making narrow-row cultivation of “Enrei” was judged to be 8.9–13.3 plants m–2 to avoid lodging, and that of “Ayakogane” 13.3–26.7 plants m–2 to promote seed yield.
