Black soldier fly frass fertilizer outperforms traditional fertilizers in terms of plant growth in restoration in Madagascar

Black soldier fly frass (BSFF) is a nutrient-rich organic byproduct with growing potential as a sustainable fertilizer. While its effects on crops have been studied, its impact on tree seedling development for reforestation remains poorly understood. This study evaluated the effect of BSFF on the growth and survival of two native Malagasy tree species: the fast-growing <i>Dodonaea madagascariensis</i> and the slow-growing <i>Verpis macrophylla</i>. A six-month nursery experiment tested three BSFF application rates (half-, one-, and two-fold nitrogen equivalence), along with cattle manure, synthetic NPK, and a no-fertilizer control. Seedling survival was highest under the lowest BSFF dose, while the two-fold BSFF and NPK treatments significantly reduced survival. Growth responses, including height, diameter, leaf number, and biomass, were significantly enhanced in <i>D. madagascariensis</i> under the half- and one-fold BSFF treatments, with effects stronger than those of cattle manure and NPK. In contrast, <i>V. macrophylla</i> showed limited response. These findings indicate that calibrated BSFF application can enhance seedling performance in reforestation efforts, particularly for fast-growing species. Notably, the growth rate of <i>D. madagascariensis</i> doubled (in terms of cm/month) under optimal BSFF treatment- a critical advantage, as time is a key constraint in reforestation and faster growth directly supports more efficient forest restoration. This highlights BSFF’s potential as a sustainable and locally available input for forest restoration in Madagascar.