Biochar Placement Depth Affects Nitrogen Use Efficiency under Fertilizer Deep Placement in Chinese Cabbage

다국어 초록 (Multilingual Abstract)

This study investigated the effects of nitrogen (N) deep fertilization and biochar placement depth on growth and nitrogen use efficiency (NUE) of Chinese cabbage (Brassica rapa L.) in a pot experiment. Biochar was applied either to the topsoil (5-10 cm) or at the fertilizer placement depth (25 cm) under a deep fertilization system. The results demonstrated that top biochar application in combination with deep fertilization significantly enhanced shoot biomass, nitrogen uptake, and NUE, which may be attributed to improved soil physical conditions that facilitated more efficient utilization of deep placed nitrogen. In contrast, biochar applied at the fertilizer placement depth increased root biomass but did not enhance shoot growth or NUE, likely due to adsorption of inorganic nitrogen by biochar. The response under reduced nitrogen input varied depending on biochar placement depth. These results indicate that the combined effect of biochar and deep fertilization depends on biochar placement depth and nitrogen supply level.