Ultisol is a type of soil with low fertility, acidic pH, low exchangeable bases, and high aluminum (Al) content, making it less optimal for plant growth. One approach to improving the fertility of Ultisol is by adding organic materials such as humic acid-biochar and SP-36 fertilizer. This study aims to determine the effect of humic acid-biochar and SP-36 fertilizer application on phosphorus (P)…