Amelioration of Nutrients and Immobilization of Cd in Cd-Polluted Loessial Soil (Sierozem) Using Biochars Derived from Different Biomasses

Abstract Biochar has special physicochemical properties and has been widely used as a soil amendment to improve the quality of soil and remediate the soil polluted with heavy metals. However, there is still a lack of research on the amelioration effects of biochars prepared from different feedstocks on single and composite heavy metal contaminated soils. Incubation experiments were used to explore the effects of different levels (0, 1 3, 5, and 10%) of biochars derived from rape straw (RS600), flax straw (FS600) and chicken manure (CM600) on the nutrients and distribution of Cd speciation in Cd single (Cd) and Cd–Pb composite (Cd + Pb) contaminated loessial soil (sierozem) and to evaluate the amelioration and remediation effects. Available potassium was positively correlated with the amount of biochars (p < 0.001). Application of RS600 and CM600 could increase the contents of available phosphorus. The additions of 3 and 5% biochars reduced available nitrogen contents. The contents of Cd residue fraction were positively correlated with the application of biochars (p < 0.001), and the contents were lower than that of Cd single contaminated soil in the Cd–Pb composite contaminated. Biochars enhanced the binding strength indexes of Cd and reduced its availability coefficients. Therefore, biochar can improve soil nutrients and reduce the bioavailability of heavy metals, thus amending the soil quality. CM600 was the most effective type of biochar in this research. The study might provide further scientific basis for biochar amelioration and remediation for heavy metal contaminated soils.