Assessing the efficacy of Arthrospira maxima biofertilizers and commercial alternatives on cash crop growth

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.