2026 Volume 49 Pages 45-50
Phosphorus is essential for food production; however, Japan depends heavily on imported phosphorus resources, highlighting the need to establish a sustainable phosphorus recycling system. Sewage-sludge-derived fertilizer is one of the potential domestic phosphorus resources, but its phosphorus availability is lower than that in chemical fertilizers, and its fertilization efficiency has not been fully elucidated. In this study, a komatsuna (Brassica rapa var. perviridis) cultivation experiment was conducted to evaluate the phosphorus fertilization efficiency of sewage-sludge-derived fertilizer. Plant phosphorus uptake and soil available phosphorus were analyzed. The results showed that sewage-sludge-derived fertilizer alone exhibited a fertilization effect; however, komatsuna growth was limited by nitrogen deficiency. When nitrogen conditions were equalized through combined application with a chemical fertilizer, the phosphorus fertilization effect of sewage-sludge-derived fertilizer was confirmed. On the other hand, when applied at the standard fertilization rate, sewage-sludge-derived fertilizer resulted in lower plant growth than chemical fertilizer, suggesting lower phosphorus availability from sewage-sludge-derived phosphorus. However, chemical fertilizers are highly mobile and prone to phosphorus leaching from the rhizosphere through irrigation. In contrast, the application of sewage-sludge-derived fertilizer may promote the accumulation of less readily available forms of phosphorus in the soil.
