The aim of this study was to consider the growth of water spinach when adding rice husk biochar was adsorbed ammonium (NH4+) of biogas wastewater. The experiment was completely randomized with 6 treatments and 4 replicates: (1) Applying 100% of rice husk biochar was not absorbed ammonium, (2) Applying 100% inorganic fertilizer (As recommended by the Ministry of Agriculture and Rural Development), (3) Apply 50% of rice husk biochar was absorbed ammonium + 50% inorganic fertilizer, (4) Apply 75% of rice husk biochar was absorbed ammonium + 25% inorganic fertilizer, (5) Apply 100% of rice husk biochar was absorbed ammonium, (6) Apply 125% of rice husk biochar was absorbed ammonium. The study results were showed that the treatments of adding ammonium-adsorbed rice husk biochar was growth and yield both increased compared to the addition of non-ammonium-adsorbed biochar. The best amount of biochar and manure for the growth of water spinach was 50% of rice husk biochar was adsorbed ammonium and 50% inorganic fertilizer. In short, it is possible to make use of rice husk biochar was adsorbed ammonium of biogas wastewater to replace a part of inorganic chemical fertilizers, which is very useful for agriculture and contributes to reducing environmental pollution.