Evaluation of corn-soybean inter-cropping systems in southwestern Japan

To assess the effects of inter-cropping corn and soybean under southwestern Japan's climatic conditions, 5 different treatments were compared, namely: CW (mono-cropped corn weeded); CTW (corn + soybean cv. Tachinagaha weeded); CT (corn + soybean cv. Tachinagaha unweeded); CSW (corn + soybean cv. Suzukaren weeded); and CS (corn + soybean cv. Suzukaren unweeded). Parameters measured were plant height, yield, nutrient composition of corn and soybean and the numbers of Japanese beetles (Popillia japonica). Plant height of mono-cropped corn was significantly (P 0.05) greater than that of corn in most of the inter-cropped treatments. The number of Japanese beetles had increased dramatically, especially on unweeded inter-cropped treatments, at 55 DAS (days after sowing). Fresh and dry matter yields (FMY and DMY) of corn did not differ among treatments (P 0.05) than in CSW and CS. Weeding tended to reduce the number of Japanese beetles on soybean plants, but it did not affect yield of soybean in this study. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations in corn cobs, whole corn plants and whole soybean plants did not differ among treatments (P 0.05), while crude protein (CP) concentration in whole corn plants in CTW exceeded (P<0.05) those for mono-cropped corn and CSW treatments. These results indicated that soybean can be successfully inter-cropped with corn in southwestern Japan. Soybean plants may be infested with Japanese beetles. It is advisable to control weeds in the stands to reduce the level of beetle infestation and to minimize competition for the planted crops.