Combined biochar and soda residues increases maize yields and decreases grain Cd/Pb in a highly Cd/Pb-polluted acid Udults soil

Abstract

Excessive heavy metal (HM) in soil limit crop yields and reduce quality of crops and soil. In this study, a 3-year field experiment was conducted to verify the effects of different amendment treatments on the accumulation and distribution of cadmium/lead (Cd/Pb) on maize aboveground parts and the availability of Cd/Pb in Udults soil. The treatments were CK, biochar at 5, 10, 20, 30 t ha−1 (B1–B4), soda residues at 3 t ha−1 (M) and biochar & soda residues (10 t ha−1 + 3 t ha−1; B2M). The results show that the greater the applied biochar dose, the longer lasting the mediating effect; however, the B2M treatment was the most effective and had the longest-lasting effects. Compared to CK, the B2M treatment significantly increased soil pH and total organic carbon levels by 0.68–1.44 pH units and 16.2 %–30.3 %, respectively, and reduced available Cd/Pb by 52.4 %–68.6 % and 28.3 %–40.8 %, respectively. Additionally, B2M also increased the maize grain yield by 7985.2–10,728.9 kg ha−1 and decreased the Cd/Pb contents of maize grains by 0.16–0.21 mg kg−1 (Cd) and 0.05–0.51 mg kg−1 (Pb) over the 3-year period. The Cd/Pb contents in maize grain were lower than the feed additive standard (GB 13078−2017), indicating that this product can be used as animal feed. Soil pH was the most important factor to control Cd/Pb accumulation, while the Cd was also influenced by biochar physicochemical properties such as specific surface area, aromatic structures and oxygen-containing functional groups. A cost analysis for this field experiment revealed that applying combined biochar and soda residues to polluted soil had an economic benefit whereas the application of biochar alone did not.