Improvement of Rice Husk Residue Silicon Availability for Replenishing Available Silicon in Paddy Soil

Increasing agricultural land area has proven beyond every reasonable doubt that it is not the solution to low yield in agricultural produce. Soil management strategies could improve the productivity and also enhance sustainability. Today’s soil management strategies depend solely on inorganic chemical-based fertilizer which is inaccessible to many small-scale farmers, due to its high cost. The use of rice husk biochar (RHB) from rice husk residue (RH), produced through the process of pyrolysis, could be one of the possible cost-effective soil management strategies in rice-based farming system. In this study, a pot experiment was conducted in the Experimental Glasshouse, Shimane University, Japan (35°29´14.30N and 133°04´07.92E) during the summer season (June to September 2017) to investigate how changes in nutrient compositions of RH pyrolyzed at different temperatures (300°C, 400°C, 500°C, 600°C and 700°C) influence rice plant agronomic parameters, soil available silica and plant silica uptake. The experimental units were replicated three times and arranged in a completely randomized design. The RH and RHB used were slightly acidic to alkaline (6.8 – 10.7). They contained elevated nutrients in comparison to the soil. The RHB treatments were found not to have much influence on the plant agronomic parameters this time. The soil available silicon after harvest could be improved or at least maintained with RHB treatments. For instance, RHB at 400°C increased the soil available Si by 61% compared to the original content (93.8 mg SiO2 pot-1). This implies that RHB could create a potential biogenic silicon pool in a paddy field. The RHBs increased soil Si availability for rice growth through an increment of plant Si uptake and soil available Si against the control. The highest increment against the control during the cropping season was found in RHB at 500°C (455.9 mg SiO2 pot-1). Finally, charring of RH by controlling the heating temperatures is an effective way of improving RH as Si amendment.