Effects of Biochar Application and Bamboo Vinegar Concentration on Growth, Quality, and Iron Content of Red Spinach Microgreens (Amaranthus tricolor L.)

The increasing demand for nutrient-dense vegetables under conditions of limited agricultural land requires sustainable cultivation approaches that support yield and nutritional value. Red spinach microgreens are considered a promising functional food; however, their performance may be influenced by growing media quality and cultivation inputs. This study evaluated the effects of bamboo biochar application and different concentrations of bamboo vinegar on the growth, sensory quality, and iron (Fe) content of red spinach (Amaranthus tricolor L.) microgreens. A factorial (2 × 6) experiment in a completely randomized design was conducted using cocopeat as the growing medium, with biochar application (with and without) and bamboo vinegar concentrations of 0, 50, 100, 200, 400, and 800 ppm. No significant interaction between biochar and bamboo vinegar was detected. Biochar application significantly improved overall plant growth and sensory attributes compared with the non-biochar treatment. Bamboo vinegar significantly affected plant height and fresh biomass, with the highest responses observed at 200–800 ppm for plant height and at 800 ppm for fresh weight. Iron content ranged from 202.09 to 481.66 ppm and was expressed on a fresh weight basis, which may be influenced by plant water content and thus limits direct comparison with studies reported on a dry weight basis. Therefore, Fe values in this study should be interpreted comparatively within treatments rather than as absolute nutritional equivalence to mature plants or other studies. Under the conditions of this study, biochar and selected bamboo vinegar concentrations showed potential to improve red spinach microgreen production and may contribute to low-input urban agriculture systems.