Poultry litter biochar soil amendment affects microbial community structures, promotes phosphorus cycling and growth of barley (Hordeum vulgare)

Phosphorus (P) is a non-replaceable, finite component of fertilizers. The imbalanced resource distribution and possible depletion of P impose challenges on current crop production worldwide. The aim of this study was to assess the impact of poultry litter biochar on plant growth and P mobilizing capability of the microbiome in comparison to a mineral fertilizer application. Spring barley (Hordeum vulgare) was grown in microcosms using a P-limited soil, fertilized with 0 (control), 50 (fertilizer) kg P ha⁻¹ or a poultry litter biochar amendment (biochar, 2% w/w). Biochar amended rhizospheres had significantly higher phosphonate-utilizing bacteria, phoC and phoD gene (acid and alkaline phosphatase) copy numbers and improved P availability. Spring barley dry matter yields were significantly higher for biochar and fertilizer over control; however, P uptake with biochar was higher than with fertilizer. Furthermore, biochar had higher arbuscular mycorrhizal colonization and significantly raised soil pH. Fingerprint-analysis showed significant differences between all treatments for bacterial and fungal communities. 16S rRNA gene-based sequencing analysis revealed increased relative abundance of the phyla Actinobacteriota and Chloroflexi in biochar compared to control, potentially contributing to the ameliorated plant growth conditions. Pearson correlations of both phyla was positive with a range of P cycling variables as well as Morgan's P but negative with acid phosphatase activity. FAPROTAX analysis revealed positive correlations of aromatic compound degradation with phoC and phoD gene abundance, highlighting a possible link between biodegradation and P release. In conclusion, poultry litter biochar could potentially replace mineral P fertilizer for sustainable plant growth in P depleted soil environments.