Photovoltaic cell-derived silicon fertilizer and its combined effect with silicate-dissolving bacteria Bacillus aryahattai on rice growing during the tillering stage

The widespread retirement of crystalline silicon solar cells in coming years poses a significant obstacle to sustainable development. Arable soils have experienced a gradual decline in available silicon levels due to intensive agricultural production. Therefore, it is feasible to repurpose recovered waste crystalline silicon cells below cell-reuse benchmark into agriculturally usable resources. This study investigates the impact of photovoltaic crystalline silicon-derived fertilizer (Si group), external silicate-dissolving bacteria (Bac group), and their combination (All group) on early rice nutrient uptake, growth development, and soil physical and chemical properties through a 45-day potting experiment. The combined addition of silicon fertilizer and bacteria significantly improved soil nitrification process (nitrate nitrogen NO₃-N increased by 73.5%) and soil organic matter content by 16.2%. The increases in soil-available silicon (by 14.9%) and total potassium (by 19%) in the All and Si were significant. For rice growth, the addition of silicon fertilizer did not have a positive effect on dry matter accumulation and plant height possibly due to the Si threshold effect or K stress. However, the chlorophyll content of the Bac and All treatment groups was enhanced by 25% and 29%, respectively, suggesting the positive effect of bacteria on soil nitrogen utilization. The absorption of potassium by the plants was positively correlated with silicon, and the accumulation of silicon reduced the carbon content of the rice's aboveground parts by 7.3% to 9.0%. The study provides a feasible solution of recycling and reusing waste crystalline silicon in agricultural applications, and the results also have indicative significance for the sustainable rice production under non-stress environmental conditions.