Growth and yield of a supernodulating soybean cultivar "Sakukei 4" in Miyagi prefecture - Effects of planting density

The supernodulating soybean cultivar "Sakukei 4" is considered to be potentially high-yielding because of its superior capability of nitrogen fixation and photosynthesis. Despite these desirable traits, Sakukei 4 was found to exhibit inferior initial growth under conventional culture conditions. To explore the method of high-yielding cultivation of this cultivar in Miyagi, we conducted two experiments (Exp.1, 2) at two locations in different years (Naruko · 2003 and Sendai · 2004). Sakukei 4 was grown at two planting densities (standard and dense planting densities), and its growth and yield were compared with its parental normally-nodulating cultivar "Enrei" and non-nodulating genotype "En1282". In Exp.1 (Naruko · 2003), dense planting increased significantly the growth (dry weight) and leaf area index (LAI), irrespective of cultivars, but it significantly increased yield only in Sakukei 4. In Exp.2 (Sendai · 2004), dense planting increased significantly the growth and LAI of Sakukei 4, but it failed to increase the yield of any genotype examined. The yield of the three genotypes tested in both experiments tended to be Enrei > Sakukei 4 > En1282 in this order, refl ecting the difference of dry weight at fl owering and seed-filling stages. The number of nodes, pods and seeds, and seed-set percentage of main stem were markedly increased by dense planting in both Sakukei 4 and Enrei, but the number of branches was increased only in Enrei. In conclusion, increasing planting rate was effective for increasing the yield in Sakukei 4 to some extent, but the yield of Sakukei 4 failed to exceed that of Enrei. The growth of branches at dense planting rate in Sakukei 4 was inferior to that in Enrei, suggesting that cultivation conditions to enhance yield components on the main stem might be effective for the high-yielding cultivation of Sakukei 4.