Microalgae biomass as a conditioner and regulator of soil quality and productivity

Characteristics of an acid soil cultivated with Uruchloa brizantha cv. Marandu were evaluated in relation to two types of fertilization: a conventional one, chemical based on nitrogen and potassium, and a biological one, based on microalgae biomass. The results were compared among three treatments: control, conventional, and biological fertilization, with seven replications each. The study evaluated microalgae community, total carbon and nitrogen contents, mineral nitrogen, and enzymatic activity. Chlorella vulgaris showed the highest organism density, which can be explained by its rapid growth and high resistance. The highest species diversity was detected in the control 1,380,938 org.(cm 3 ) −1 and biological 1,841,250 (org.(cm 3 ) −1 treatments, with the latter showing a higher density of cyanobacteria, especially Pseudanabaena limninetica with 394,554 org. (cm 3 ) −1 . The soil treated with chemical fertilization showed higher nitrate (9.14 mg.NKg − 1 NO 3 − -N) and potassium (52.32 mg.dm − 3 ) contents. The highest levels of sulfur (21.73 mg.dm − 3 ) and iron (96.46 mg.dm − 3 ) were detected in the biological treatment. The chemical treatment showed higher activity of the enzymes acid phosphatase, acetilglucosaminidase, and sulfatase, while α-glucosidase and leucine-aminopeptidase stood out in the biological treatment. Soil properties were not significantly affected by the treatments. The use of microalgae biomass derived from wastewater treatment from milking parlors was evaluated and presented as a promising fertilizer for agriculture, following the line of recovering nutrient-rich wastes. In this sense, although many challenges need to be overcome, the results suggest that microalgae-based fertilizers could lead to low-impact agriculture.