Turning waste into resilience: the effect of black soldier fly larvae frass and wheat straw biochar on bell pepper growth, soil fertility and rhizosphere bacteria under water stress

Abstract

Background and aims: Drought significantly limits crop productivity, highlighting the need for sustainable soil management. Black soldier fly larvae frass and biochar (a nutrient- and carbon-rich amendment) can increase plant productivity, but their combined effects under drought stress are poorly understood. Methods: The experiment was designed to evaluate the effects of three factors on bell pepper (Capsicum annuum L.) growth, soil fertility, and rhizosphere bacteria: frass type (vegetable- and manure-derived), biochar presence (with or without), and water supply levels (well-watered at 70% and water-stressed at 35% field capacity). The experiment was conducted in a temperature-controlled glasshouse for 10 weeks. Results: At harvest, shoot dry weight significantly increased by both frass types under both water supply conditions compared to the control. However, vegetable-derived frass resulted in greater shoot dry weight than manure-derived frass under well-watered conditions, whereas no significant difference was observed under water-stressed conditions. Biochar significantly increased shoot dry weight and shoot N content than without biochar. Frass increased shoot N content, soil NH4+ -N, NO3− -N and dissolved organic carbon. Water stress decreased microbial biomass nitrogen, whereas both frass types increased the microbial biomass nitrogen and carbon. Co-applying biochar with manure-derived frass increased soil pH than frass alone. Under water-stressed conditions, combining frass with biochar enriched the relative abundance of bacterial genera, such as Porphyrobacter and Sphingomonas, which are associated with drought stress resilience. Conclusion: This study highlights the potential of integrating frass and biochar as sustainable soil management strategies to enhance crop production under varying water conditions.