Evaluating potential of green alga Chlorella vulgaris to accumulate phosphorus and to fertilize nutrient-poor soil substrates for crop plants

Algae are capable of accumulating nutrients from aqueous waste, which makes them a potential fertilizer. The ability of the fast growing Chlorella vulgaris strain IPPAS C1 to accumulate phosphorus (P) was probed in V-shaped plastic foil photobioreactors. The P uptake was 0.13–0.53 g(P)·m⁻²·day⁻¹ when the algal culture densities were kept between 0.1 and 1.0 g(DW)·L⁻¹ in a typical summer irradiance of Central Europe. The algal biomass can be effectively utilized for soil fertilization only if the algal cells release nutrients into the soil in a form that would be available to roots and at a rate sufficient to support plant growth. To examine this, we compared the growth of wheat, Triticum aestivum L., in two nutrient-deficient substrates: “Null Erde” and sand, with and without fertilization by wet and spray-dried algae. Plants grown in the two nutrient-deficient substrates supplemented by mineral fertilizer served as a control representing optimal nutrient supply. Plants grown in a high-nutrient substrate (SoMi 513) were used as an additional reference representing the maximum growth potential of wheat. Wheat growth was monitored for 8 weeks and measured, including the increase of the leaf area as well as shoot and root dry weight in 10 randomized replicates for each substrate and fertilization variant. After harvest, the biomass and N, P, and C contents of the plant shoots and roots were recorded. Algae fertilization of “Null Erde” led to wheat growth, including root hair production, which was similar to mineral-fertilized “Null Erde” and only slightly less vigorous than in the nutrient-rich SoMi 513 substrate. The plants grown in sand were smaller than the plants in “Null Erde” but fertilization by algae nevertheless led to growth that was comparable to mineral fertilizer. These results unambiguously demonstrate that algal biomass is a viable option for delivering nutrients to support agriculture on marginal soils.