<![CDATA[Ultisol is an acidic soil with relatively low nutrient content, requiring soil improvement efforts to support plant growth. One alternative is the application of oil palm empty fruit bunch (OPEFB) biochar combined with nitrogen fertilizer. This study aimed to determine the combination of OPEFB biochar and nitrogen fertilizer doses that provides optimal growth of pakcoy (*Brassica rapa* L.) cv. Nauli F1 grown on Ultisol soil. The study was conducted from February to July 2025 on agricultural land located on Jl. Raya Teluk Jambe, Sirnabaya, Telukjambe Timur. The research used a randomized complete block design (RCBD) with a single treatment factor consisting of nine treatments and three replications, resulting in 27 experimental units. The treatments consisted of combinations of OPEFB biochar at 0, 10, and 20 tons/ha and nitrogen fertilizer at 0, 200, 300, and 400 kg/ha. Data were analyzed using analysis of variance (ANOVA), followed by Duncan’s Multiple Range Test (DMRT) at the 5% significance level when significant differences were detected. The results showed that the combination of OPEFB biochar and nitrogen fertilizer significantly affected plant height, number of leaves, and stem diameter at 14, 21, and 27 days after planting (DAP). Treatment I (20 tons/ha OPEFB biochar + 400 kg/ha nitrogen fertilizer) resulted in 24.58 cm plant height, 15.07 leaves, and 7.65 mm stem diameter at 27 DAP. The combination of 20 tons/ha OPEFB biochar and 400 kg/ha nitrogen fertilizer has the potential to improve pakcoy growth.]]>
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