Localized fertilizer co-applied with biochar suspension increases phosphorus uptake by maize

<title>Abstract</title> <bold>Background and aims</bold> Integrating biochar (BC) into agriculture promotes sustainable management of farm residues and carbon sequestration in soil. This study evaluates a novel approach combining suspended biochar with phosphorus (P) fertilizer to assess its effectiveness in promoting P nutrition during early maize (<italic>Zea mays </italic>L<italic>.</italic>) growth. <bold>Methods</bold> Biochar suspension (equivalent to 300 kg dry biochar ha^-1) was mixed with liquid P fertilizer (30 kg P ha^-1, ³³P-labeled) and band-applied to maize in the rhizobox experiment. Five treatments—control without fertilizer, BC only, P fertilizer only, and combined BC+P with and without plants—aimed to assess the effect of biochar on soil P dynamics and plant P uptake. <bold>Results</bold> Our findings demonstrate that liquid P fertilizer can be effectively combined with biochar suspension without reducing P availability. After 38 days, up to 25% of fertilizer-P was recovered in the soil’s available P pool, regardless of BC presence. ³³P-imaging confirmed that P movement from the fertilizer band was not restricted by BC. Fertilizer increased plant P uptake, height, biomass, leaf area, root length and volume. Biochar significantly increased fertilizer-P recovery in plants from 14.9% to 17.6%, supporting nutrient cycling and fertilizer efficiency. ³³P-imaging revealed higher activity of ³³P in maize roots with BC+P co-application, though P redistribution patterns remained unchanged; plant roots showed neither preference nor suppression near biochar, even upon direct contact. <bold>Conclusion</bold> Localized co-application of biochar and P in suspension promotes maize growth during critical early stages and increases phosphorus use efficiency, supporting sustainable agriculture and a circular economy.