¹Graduate School Program, Faculty of Agriculture, Universitas Sebelas Maret, Indonesia

²Soil Science Department, Faculty of Agriculture, Universitas Sebelas Maret, Indonesia

Email: herywidijanto@staff.uns.ac.id

Biochar can be used as a soil amendment and source of Si. The content of Si biochar differs depending on the raw material. The research aimed to know the effect of biochar kinds on available- silicon in different soils in a flooded condition. The experiment used a complete randomized design (CRD) with 2 factors. Biochar type consists of B1 = rice straw; B2= rice husk; B3 = sawdust ; B4= coconut shell ; B5 = corn stover. Soil type consists of T1: Inceptisol and T2: Ultisol. Each treatment is replicated three times. The experiment used 2 kg of soil and 5 tons.ha^-1 biochar. Incubation is carried out for four weeks by maintaining a water height of 5 cm. Soil parameters include organic C, total N, available P, total Si, available Si, leached Si, and pH H2O. The data were analyzed using Analysis of Variance, Duncan’s Multiple Range Test, and Correlation test. The results showed that biochar from rice husks has a higher total Si and Si available than other biochar. Rice husk biochar gives the highest available-Si in Inceptisol (8.66 mg/kg) and Ultisol (7.49 mg/kg) compared to the other biochar. Silicon leaching ranges from 5.23-8.66% of soil available-Si in both soils.