Change in Substrate Macronutrients and Growth Traits as Affected by Companion Cropping Ratios of Perilla with Kidney Bean in Container Cultivation

This study investigated the effects of companion cropping on substrate macronutrient content and on plant growth when perilla (Perilla frutescens L.) was grown as the main crop and kidney bean (Phaseolus vulgaris L.) as the companion plant. Five treatments were established according to planting ratio: perilla monoculture (PC); perilla and kidney bean mixtures at 2:1 (P2K1), 1:1 (P1K1), and 1:2 (P1K2); and kidney bean monoculture (KC), all grown in containers under greenhouse conditions. Companion planting with kidney bean improved neither substrate macronutrient status nor the growth of perilla in containers. Substrate analysis showed that macronutrients (nitrogen, phosphorus, and potassium) declined significantly and rapidly in the mixed treatments relative to the perilla monoculture (p < 0.05). Compared with the monoculture, companion cropping with kidney bean significantly reduced the leaf length, leaf width, leaf number, chlorophyll content, chlorophyll fluorescence, stem diameter, and biomass of perilla (p < 0.05). The land equivalent ratio (LER) did not differ significantly among the P2K1, P1K1, and P1K2 treatments, although the relative yield (RY) and competitive ratio (CR) of kidney bean decreased with decreasing perilla cropping ratio, indicating that kidney bean was more competitive than perilla. Perilla monoculture is therefore more suitable than companion planting with kidney bean for short-duration container vegetable gardening.