Environmental and economic assessment of nitrogen-fixing Nostoc sp. as a sustainable alternative to synthetic urea fertilization

Abstract

This study investigated the environmental impact and discussed the economic aspects of substituting synthetic urea (S1) with nitrogen-fixing Nostoc sp. in two agricultural systems: slow-release fertilization (S2) and external nutrient extraction in the form of biogas digestate (S3), which allows for more efficient use of nutrients by plants. The carbon dioxide (CO₂) sequestration rate was determined experimentally, while actual outdoor productivity data were obtained from the literature and analyzed for uncertainty. The results showed that replacing one ton of traditional synthetic urea with microalgae-based alternatives (S2 and S3) significantly mitigated global warming potential from 5.4 to 2.3 tons CO_2-eq in S2 and achieved net carbon sequestration of −1.1 tons CO_2-eq in S3 when using biogas in anthropogenic activities. Furthermore, S2 and S3 mitigated the impact of human non-carcinogenic toxicity by 51.0 % and 48.1 %, respectively. However, these alternatives consumed higher water amounts and increased land use significantly. The current cost of equivalent microalgal biomass production is approximately five times higher than the price of urea. Therefore, substituting chemical fertilizer of urea with a natural alternative based on N-fixing Nostoc sp. is not economically feasible at present, despite its positive environmental benefits.