The potential of rice husk-derived biochar as a bio-silica source in the agricultural area of Tuban, East Java

Rice husk, accounting for about 20% of total paddy biomass, remains an underutilized agricultural residue despite its abundance. This study explores the conversion of rice husk into biochar through pyrolysis under limited oxygen conditions, focusing on biomass yield and physicochemical characteristics for agronomic use. Biochar is valued for its carbon content, soil-enhancing ability, and contribution to sustainable agriculture. Biomass analysis of rice showed an aboveground yield of 95.06 g per plant (grain: 43.20 g; straw: 51.86 g) and belowground biomass of 39.06 g (root). Soil nutrients included nitrogen (0.41%), phosphorus (53.8 mg/100 g), potassium (137.40 mg/100 g), and organic carbon (4.54%), influencing biomass accumulation and plant physiology. Pyrolysis at 250 C was conducted using a controlled furnace, and the resulting biochar's composition was analyzed via X-Ray Fluorescence (XRF). The biochar contained high silica (SiO₂: 80.03%), with P₂O₅ (3.07%), K₂O (10.38%), CaO (5.16%), and trace elements such as MnO, Fe₂O₃, CuO, ZnO, and ZrO₂. It also exhibited a water holding capacity of 81.09% and a pH of 6.23, indicating its potential as a soil amendment and nutrient carrier. These results demonstrate the dual role of rice husk biochar as a bio-silica source and soil enhancer, promoting sustainable residue-based agriculture in East Java.