Evaluation of Soybean (Glycine max) Stem Vining in Maize-Soybean Relay Strip Intercropping System

Forming a method of judging the degree of soybean vining in the intercropping system is very important for estimating the shade tolerance of soybean germplasm and choosing the special soybean varieties for intercropping system. Thirty varieties were subjected to two treatments (sole and maize-soybean relay strip intercropping system) with three replications in a complete randomized block design. Light environment characteristics in two cropping systems were measured. At the beginning of the bloom stage of soybean when maize was mature, the soybean stem morphology characteristics stem length, node number, hypocotyl length, internode length, stem diameter, stem breaking strength and stem biomass were measured. The results revealed that the intercropped soybean could capture 13.8% photosynthetic active radiation at the vegetative stage, as compared with the sole crop soybean, with longer soybean main stem, internode and hypocotyl, and lower stem diameter at this stage. The relative value of agronomic traits in the sole and intercropping system could be used to calculate the vining severity index (VI) and the weighted vining index (WVI), and the latter could be used as the comprehensive index of the degree of soybean vining in the relay strip intercropping system. Based on the values of WVI, through the Hierarchical Cluster Analysis, the soybean varieties were divided into the 5 clusters, normal, mild, moderate, severe and extreme vining. Eight of the 30 varieties of soybean were normal vining grade and could be used as the parent plants to breed special varieties for intercropping.