Mineralization of Nutrients Following Application of NPK Green and Black Soldier Fly Larvae Frass in Bekenu Series Soil

Abstract

The integration of organic and inorganic fertilizers is essential to improve the fertility of highly weathered tropical acid soils. Soil incubation study was conducted to evaluate the mineralization of nutrients in Bekenu Series soil following the application of black soldier fly larvae (BSFL) frass in combination with NPK Green fertilizer. Results showed that combined BSFL frass and NPK Green treatments (SFN1–SFN9) significantly increased soil pH from 4.21 to 5.67–6.18, whereas BSFL frass alone slightly reduced soil pH. The highest cation exchange capacity (10.87 cmol(+) kg⁻¹) was recorded in SFN5, contributing to improved nutrient retention and balanced electrical conductivity. Organic matter content ranged from 5.80% to 16.30%, with higher mineralization observed in SF3 (16.30%), SFN3 (11.34%), and SFN4 (14.19). Phosphorus availability was enhanced particularly in SFN4, SFN1, SFN7, and SFN8. Treatments such as SFN2, SFN3, SFN4, SFN7, and SFN8 improved soil pH, nutrient availability, and overall agronomic properties. Exchangeable Al³⁺, H⁺, and Zn²⁺ remained below toxic thresholds, although slight increases were noted as soil pH declined over time. These findings highlight the potential of BSFL frass, particularly when integrated with NPK Green, to enhance nutrient mineralization and improve the fertility status of Bekenu Series soil.