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The status of heavy metals in arable soils of contrasting texture treated by biochar – an experiment from Slovakia

Šimanský, Vladimír / Jonczak, Jerzy / Chlpík, Juraj / Polláková, Nora

Worldwide, many soils are impacted by degradation processes, which impose a risk to sustainable food production. There is a pressing need to limit these negative impact constraints to sustain the proper functioning of the soil-biota system and soil productivity. Biochar can be a nature-friendly solution for soil remediation; however, knowledge is incomplete in many aspects in this field, like the potential of biochar and biochar-based products as agents to immobilize toxic substances, including heavy metals (HMs) found in the soil. In this study, we investigated the effect of two biochar substrates (BSs) (1. biochar blended with farmyard manure as BS1, and 2. biochar blended with farmyard manure and digestate as BS2) at rates of 10 and 20 t ha⁻¹ applied without or with fertilization (BS + F) on the immobilization of HMs in texturally different soils (1. sandy Arenosol, 2. loamy Chernozem, Slovakia). The results showed that application of BS had different effects in relation to soil textures. In sandy soil, BS improved soil properties, such as cation exchange capacity (an increase from 20 to 93%), soil organic carbon content (SOC) (an increase from 3 to 26%) and humic substances (HSs) stability (an increase from 12 to 20%). In loamy soil, SOC increased due to BS and BS + F in the range 3–19% and 12–55%, respectively. In both soils, the total content of HMs did not exceed the threshold limits for individual soils after BS and BS + F application. In sandy soil, the immobilization of HMs was due to a higher SOC content and a fulvic acids (FAs) content, while in loamy soil their elimination depended on a higher available phosphorus content.