Understanding Cyanobacteria-based Biofertilizers in Soil-Water and Soil-Plant Systems

Abstract

Growing pressures to increase agricultural productivity amid rising environmental impacts and global climate threats call for critical strategies that preserve the soil resource and improve sustainability. Microalgae, including cyanobacteria, are emerging as promising platforms to enhance soil structure and fertility and reduce our reliance on chemical fertilizers. To advance applications, further understanding is needed with different strains, plants, agroecological regions and types of soil including Mollisols, which are among the most productive soils in the world. This dissertation reviewed aspects of microalgae that might be applied in agriculture and evaluated effects of soil inoculations with the dinitrogen (N2)-fixing cyanobacterium Anabaena cylindrica UTEX 1611 on a Mollisol from the U.S. Upper Midwest. First, a comprehensive literature review supported microalgae as renewable resources for the potential development of biofertilizers, organic fertilizers, biostimulants, biocontrol agents, and soil conditioners. Furthermore, experiments with cyanobacterial soil inoculations described effects on soil structure and nutrient dynamics, soil loss and water nutrient levels after high-intensity rain simulations, and soil mineralization of cyanobacterial biomass. The results revealed changes in soil structural components that might be resistant to wind and water erosion, potential for reducing rainfall-induced soil loss, and a gradual nutrient release from the cyanobacterial biomass. High-intensity rain simulations also indicated depth-related positive changes in soil microbial dynamics that persisted after consecutive rains. Finally, experiments with a local variety of spring wheat consistently evidenced improvements in soil nutrients, microbial biomass, and microbial activity, and demonstrated that cyanobacteria, and a mixture with a local green microalga, supplied nitrogen (N) to support plant growth and partially replace urea. These findings provide insights on the positive role cyanobacteria might have as resources to enhance the sustainability and resiliency of agricultural systems.