Evaluation of regrowth ability of soybeans for forage utilization under two-cutting systems

Abstract

Soybean (Glycine max) has the potential as forage feed because of its high protein content and low fiber. Intercropping soybean with tropical forage grasses can improve forage quality and increase yield. However, their optimum cutting interval under mixed cropping system is still unknown. This study aimed to investigate regrowth ability and performance of soybean plant under two different cutting heights in Miyazaki, Southwestern of Japan, which has a humid subtropical climate with relatively high temperature and evenly distributed precipitation throughout the year. The experimental design was randomized block design arrange in 3  2 factorial scheme (soybean cultivars  cutting treatments). Three soybean accessions (Glycine max ‘Fukuyutaka’, G. max ‘Kohamdaizu’ and G. gracilis ‘Moshidou Gong 503’) with 5 replications were cultivated under single seeding condition. Soybeans were defoliated after 50 d of cultivation under low level cutting height (LC, 7.5 cm) and high level cutting height (HC, 12 cm). ‘Fukuyutaka’ achieved 100% regrowth rate in both LC and HC. Although the regrowth rate for ‘Kohamadaizu’ was 100% in the HC, it was only 20% in LC. ‘Fukuyutaka’ was more robust and high tolerant for defoliation stress than that of ‘Kohamadaizu`. In other hand, no plants exhibited regrowth in both cutting heights for ‘Moshidou Gong 503’. For ‘Fukuyutaka’ and ‘Kohamadaizu’, the number of branching nodes with re-emergent leaves was significantly higher in the HC. In both cutting height of ‘Fukuyutaka’, plant continued elongating and exhibited vigorous growth until 2nd cutting. The cutting height levels, height of cotyledonary node and growth stage of soybean plant when harvested at the 1st cutting significantly affected the regrowth ability of soybeans. In conclusion, ‘Fukuyutaka’ showed the ability for regrowth under LC and HC. HC provided significantly higher fresh matter and dry matter weight than that LC. Further study is needed to evaluate the performance of ‘Fukuyutaka’ under intercropping cultivation with tropical forage grasses. This is the first report to establish an approach for two-cutting soybean as forage