Microalgae Cultivated in Cattle Wastewater as a Biofertilizer: Tests on the Production of Arugula (Eruca vesicaria) and the Benefits for Sustainable Agriculture

Ensuring food security for the world's growing population while advancing sustainable agriculture and reducing conventional fertilizer use is a major challenge. The objective of this research was to comparatively evaluate the effect of microalgae biomass biofertilizer, derived from the production of Arthrospira platensis DHR 20 (Spirulina) in cattle wastewater under organic management (CW), on the development of arugula. It also examined the microbiological attributes of arugula leaves and the changes in soil chemical properties and structural composition of the soil post-experiment. The experiment consisted of three treatments: T1 – control, with urea application; T2 – CW; T3 – microalgae biofertilizer. The experimental design was completely randomized with seven replications and four plants per plot. The main conclusion of this research is that microalgae biomass biofertilizer presents nutritional potential for arugula, particularly as a source of N (187.5 mg L −1 ) and K (92.9 mg L −1 ), and can replace conventional urea fertilizer as a nitrogen source in the cultivation of arugula, with similar plant development quality according to the Dickson Quality Index. According to the SAR, the microalgae biomass biofertilizer and CW do not present soil sodicity restrictions and show a low to moderate level of restriction for soil use in terms of salinity. The average biofixation rate of 0.22 CO 2 L −1 d −1 obtained in the study suggests that Spirulina cultivation in CW is suitable for this greenhouse gas biofixation. Leaves from the three treatment groups yielded negative results for the presence of thermotolerant coliforms. Both microalgae biofertilizer and CW acted as soil conditioners, improving its structural quality when compared to soil fertilized with urea. Graphical Abstract