Black soldier fly frass (BSFF) is a circular-economy soil amendment with promise for improving soil health in perennial systems, yet multi-month field evidence in commercial fruit orchards is scarce. We report interim results from two commercial avocado blocks in Israel (Regavim; Mishmarot) designed to identify BSFF dose ranges that benefit rhizosphere function. Roots and rhizosphere soil were sampled immediately pre-treatment (Oct–Nov 2023) and ~6 months post-treatment (May 2024) from all trial trees (n=60 per block; four BSFF treatments per block). Root-associated bacterial communities were profiled by 16S rRNA amplicon sequencing (240 samples total). Bulk soil was analyzed for total C, total N and C/N.
Alpha diversity (Inverse-Simpson; Pielou) did not differ among to-be-treated groups at baseline. By May 2024, responses diverged between sites: in Mishmarot, microbial diversity decreased in the highest BSFF treatment relative to others (Wilcoxon rank-sum, p<0.05), whereas Regavim showed no among-treatment differences but did show baseline-to-follow-up shifts at intermediate/high BSFF (paired Wilcoxon, p<0.05). Community composition differed strongly between sites and between timepoints (PERMANOVA p<0.001 for each). Within May 2024, BSFF treatment explained significant compositional variation in both blocks (Regavim p=0.001; Mishmarot p=0.008). Linear-model associations (FDR<0.05) identified dose-responsive taxa: 16 in Regavim and 75 in Mishmarot. Notably, Rhizobiaceae increased in both sites; other positive associations were enriched in Actinobacteria/Alphaproteobacteria (Regavim) and Alphaproteobacteria/Gammaproteobacteria (Mishmarot). Soil total C, N, and C/N were unchanged across treatments/timepoints.
A single BSFF application produced persistent, site-specific restructuring of the avocado rhizosphere within six months, independent of bulk C/N. The consistent rise of Rhizobiaceae suggests an early microbial indicator of improved rhizosphere function. Ongoing work integrates dose–response modeling, metabarcoding for nematodes, and multi-year tree performance to define agronomically optimal BSFF rates.
