Agronomic traits and forage production in a mixed-planting with Corn for Forage Soybean Cultivars, Chookdu 1 and Chookdu 2

Soybean [Glycine max (L.) Merr.] cultivar 'Chookdu 1' (registration number: No. 7159) and 'Chookdu 2' (registration number: No. 6758) were developed as forage soybean cultivars at Kyungpook National University, Republic of Korea. They were grown in tests over three years and compared with a commercial seed cultivar for seed yield and forage productivity planted in the same row in mixed plantings with corn. Chookdu 1 and Chookdu 2 are tall, indeterminate growth habit selections from a cross between wild soybean (Glycine soja Sieb. & Zucc.), 'PI 483463', and cultivated soybean, 'Hutcheson' (PI 518664). The plant height of Chookdu 1 and Chookdu 2 were 80.9 cm and 81.4 cm, respectively, compared to 54.7 cm for the 'Pungsannamul' commercial seed check. The three-year seed yield of Chookdu 1 and Chookdu 2 was 2.0 and 2.2 t/ha, respectively, and not significantly different from Pungsannamul at 2.4 t/ha. Of the two cultivars Chookdu 2 averaged the most total forage fresh weight (65.0 t/ha). The three year mean forage yield of mixed-planting of corn and Chookdu 2 and Chookdu 1 was 10.4% and 3.8% greater, respectively, than corn monoculture. Results show Chookdu 1 and Chookdu 2 are suitable soybean cultivars for mixed planting in the same row with corn to improve forage yield. They should be useful as parents to use in breeding to develop forage-type soybeans of high quality and yield for use in livestock feed.