Organomineral fertilization with sewage sludge: heavy metal content in the soil and bioaccumulation in Urochloa brizantha

Abstract

The use of sewage sludge as biochar or compost in organomineral fertilizers has been investigated as an alternative to mineral fertilizers, as it can maintain crop yields, reduce environmental impacts, and improve soil quality. Therefore, this study aimed to evaluate the efficiency of organomineral fertilizers derived from sewage sludge and lignolytic compounds, formulated through different technologies, on the bioaccumulation of heavy metals in Urochloa brizantha cv. Paiaguás. The experimental design consisted of randomized blocks with four replications. The treatments included: granulated biochar-based organomineral fertilizer, powdered biochar-based organomineral fertilizer, granulated composted sludge-based organomineral fertilizer, powdered composted sludge-based organomineral fertilizer, mineral fertilizer, and a control (no fertilization). Root, shoot, and total dry matter were evaluated, alongside metal content and accumulation in plants, and geoaccumulation and pollution indices in the soil. All organomineral fertilizers increased biomass production to a similar extent as the mineral treatment, highlighting their efficacy as a nutrient source. Soil heavy metal analysis indicated that biochar and sewage sludge promoted accumulation levels similar to those of the mineral treatment, not exceeding the limits established by Brazilian legislation. Furthermore, the distribution of metals across plant parts (roots and shoots) was comparable across treatments, indicating that biochar and sludge did not increase metal uptake relative to mineral fertilizer management. Biochar reduced Pb availability in the soil, whereas in the mineral treatment, Pb was more susceptible to leaching.

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