Assessing the potential of algae as an alternative phosphorus fertilizer
Global phosphorus (P) reserves are finite, making the development of sustainable fertilizer alternatives critical for agricultural production. While algae biomass can supply plant-available P, its performance relative to conventional synthetic and organic fertilizers across varying soil textures and soil conditions associated with recurring crop P deficiency remains poorly understood. We conducted two incubation studies to assess the effects of dry microalgae powder on P dynamics. The first study compared Tribonema minus algae with synthetic fertilizers and a bone meal pellet across four soils differing in texture (coarse and fine) and whether they originated from fields with or without a history of recurring crop P deficiency. The second compared three algal types ( T. minus , Uronema high P, and Uronema low P) with poultry manure, hydrolyzed fish liquid, and corn steep powder in coarse and fine soils from fields with recurring crop P deficiency. Pore water P was measured over 3 months, followed by analysis of Olsen P, resin-extractable P, and microbial P at the end of each incubation. Across both studies, P availability depended strongly on soil texture, field P deficiency history, and amendment composition; soils from fields without recurring crop P deficiency and coarse-textured soils consistently showed greater pore water and resin-extractable P. In Study 1, synthetic fertilizers yielded the highest P recovery, while organic amendments released P more slowly. In Study 2 which focused on soils from fields with a history of crop P deficiency all algal types showed greater pore water P recovery than most other organic fertilizers in the coarse soil. Conversely, in fine textured soil, algae had the lowest pore water P recovery. However, by the end of Study 2, resin-extractable P recovery was greater in Tribonema than in one hydrolyzed fish product, regardless of texture. Our findings indicate that dead algal biomass is a promising P source relative to other organic fertilizers, though its performance is highly context-dependent.