Optimization of a wheat small red bean double cropping system in South Korea.

Wheat (Triticum aestivum L.) and small red bean [Vigna angularis (Willd. Ohwi & Ohashi)] are the main ingredients of walnut-shaped "Hodugwaja". An innovative wheat small red bean double cropping system was evaluated in a rice field in the Cheonan region (Korea) to determine its effect on land use. The effects of different nitrogen levels, sowing dates, and density on growth, yield, and quality of wheat and small red bean were also investigated using selected wheat ('Keumgang', 'Sooan', and 'Goso') and small red bean ('Hongeon', 'Chungju', and 'Arari') varieties. The effect of different fertilizer treatments [N1 (50%, 6.6 kg/10a), N2 (100%, 8.8 kg/10a), and N3 (200%, 13.2 kg/10a)] were investigated for wheat, while the effect of sowing date and density were investigated for the small red beans. Our findings revealed that the best variety, sowing date, and nitrogen level combination for wheat small red bean double cropping system in Cheonan area is 'Goso' sown on October 26, N3 nitrogen application, and 'Chungju' sown on July 10 with high ridge cultivation, at a density of 60 × 15 cm. This system was the most ideal yielding 521.6 kg/10a (1000 m) and 275 kg/10a of 'Goso' and 'Chungju', respectively. This pioneering research provides a reliable cultivation plan and theoretical basis for implementing the double cropping system of wheat small red beans in central Korea. Undeniably, this study also provides a basis for future field experiments on wheat planting patterns and small red bean fertilization.