José Alberto Estrada

Biofertilizers offer a sustainable alternative to chemical fertilizers, notorious for their harmful impact on the environment and human health. Sources of biofertilizers include cyanobacteria, such as those from the genus Arthrospira, which contain bioactive compounds that enhance plant growth directly and indirectly. To promote widespread biofertilizer adoption, experimental trials are essential to compare their efficacy against chemical fertilizers and different biofertilizer varieties. Some biofertilizers rely on ultrasonication for cell rupture, but since A. maxima undergoes sun‐drying to obtain the biomass powder, which also ruptures cells, ultrasonication may be unnecessary. We assessed the biofertilizer capabilities of Arthrospira maxima (Setchell & N.L. Gardner) Geitler biomass on three cash crops, banana (Musa acuminata Colla), cowpea (Vigna unguiculata L. Walp.), and eggplant (Solanum melongena Mill. Dunal). We compared sonicated and non‐sonicated biomass (both 20 g L⁻¹) against a commercially available, brown algae Ascophyllum nodosum (L.) biofertilizer (4 mL L⁻¹ OptiMar), a commercially available chemical fertilizer (1.5 mL L⁻¹ Triple15), and a negative control of tap water. Few differences were observed among A. maxima treatments, suggesting sonication might be unnecessary. OptiMar, Triple15, and the negative control did not yield the highest biometric values of any trait in any crop. If commercially available fertilizers and biofertilizers do not outperform the negative control, it raises crucial questions regarding their effectiveness and the appropriate concentrations at which they should be applied. Non‐sonicated biomass often outperformed OptiMar, Triple15, and the negative control, demonstrating the potential Arthrospira maxima has for stimulating plant growth without ultrasonication.

The continued increase in human populations and use of chemical fertilizers remain a threat to the health and stability of human–ecological systems worldwide. To ameliorate this problem and achieve long-term food security, a variety of ecofriendly technologies have been developed, including the production of cyanobacteria-based biofertilizers. This technology can be optimized through experiments that assess how plant growth is enhanced under different biofertilizer concentrations (g L⁻¹). In this study, the biofertilizer capabilities of various concentrations of sonicated biomass (0, 2.5, 5, 10, 20, and 40 g L⁻¹) derived from the cyanobacteria Arthrospira maxima on the growth of basil (Ocimum basilicum, Lamiaceae) were assessed, comparing their effectiveness with that of a positive control, a commercial biofertilizer (OptiMar Algas Marinas^®) administered at 4 mL L⁻¹. Generally, increased concentrations led to enhanced growth parameters; however, discernible differences from the negative control (0 g L⁻¹) were often observed only when concentrations exceeded 5 g L⁻¹. Surprisingly, the negative and positive controls often yielded similar results. A chemical composition analysis of A. maxima revealed high concentrations of the phytohormones, macronutrients, and essential amino acids that likely explain how our A. maxima sample enhanced growth in basil. Further research is required to determine how other crop plants respond to different concentrations of A. maxima. Additionally, assessing the feasibility of creating an economically accessible product with a higher concentration of A. maxima is crucial for practical applications.

Cyanobacteria and microalgae represent promising sources for sustainable production of biofertilizers and biostimulants, which can improve crop yield and quality and contribute to food security. However, despite their potential, their exploration remains incomplete, hindered by technical and economic challenges that arise when attempting to scale up production. The primary focus of this review is to delve into the active chemical compounds responsible for the biofertilizing and biostimulating roles of cyanobacteria and microalgae. In addition, it explores the essential unit operations involved in transforming their biomass into potential bioproducts. Moreover, this review highlights studies that have employed cyanobacteria and microalgae as sources of biofertilizer in various crops, describing their mode of action and application. By integrating cyanobacteria and microalgae processing with other advanced biotechnological, the viability of these products for sustainable agriculture can be significantly enhanced.