Recycling Reservoir Sediments and Rice Husk for Sustainable Rice Seedling Production

Amending reservoir sediments with organic matter provides a sustainable alternative to conventional rice (Oryza sativa L.) seedling substrates, simultaneously reducing dependence on agricultural soils and promoting the recycling of dredged sediments and agricultural by-products. Preliminary tests showed that adding rice husk (RH) improved the porosity and water retention of the sediments while preventing surface cracking. This study further examined the effects of RH and rice husk biochar (RHB) on sediment fertility and rice seedling growth. Seedlings were grown for 15 days in a fine- or coarse-texture sediment amended with 0, 5, 10, or 20% (w/w) RH or RHB. A 10% amendment was identified as the optimal ratio for promoting seedling growth (increasing ca. 20% biomass). Nitrogen (N) availability was the primary factor influencing seedling performance, outweighing the effects of salinity and phosphorus availability. Compared with RH, RHB amendment resulted in lower substrate available N, likely due to greater losses through denitrification and ammonia volatilization, leading to reduced growth. In contrast, RH amendment maintained higher levels of available N, resulting in greater shoot biomass and higher leaf chlorophyll concentrations. Overall, amending reservoir sediments with 10% RH provides the most effective substrate formulation, offering a practical and sustainable strategy for rice seedling production.