From manure to high-value fertilizer: The employment of microalgae as a nutrient carrier for sustainable agriculture

The use of livestock and poultry manures as fertilizers is regarded as an important action in the development of circular agriculture. However, long-term fertilization with manure is accompanied with heavy metals accumulation, pathogens contamination, and ammonia toxicity, which may cause the decline of soil quality and crop productivity. To address the aforementioned problems, in this work, we proposed a “manure-algae-crop” technical route, in which microalgae are employed as a carrier transporting nutrients in manures to soil and crops. This paper presented the advanced techniques which can tackle with the hazardous factors in manures and promote the nutrients assimilation by microalgae. Additionally, the utilization of microalgae in the forms of living cyanobacteria, liquid fertilizer, and slow-release fertilizer was discussed in detail. Particularly, we also focused on the disadvantages of algae fertilizers in different forms. By the end of this work, based on the analysis of current challenges and problems, we discussed the potential solutions and prospects of “manure-algae-crop” technical route.