Effects of Biochar on Bioavailability of Two Elements in Phosphorus and Cadmium-Enriched Soil and Accumulation of Cadmium in Crops

Abstract

Using phosphorus and cadmium enriched soil (total Cd is 0.94 mg·kg-1, total phosphorus is 0.86 g·kg-1) and low cadmium accumulation genotype Jinqiuhong 3 as experimental materials, we set up four treatments: absolute control (only NK inorganic fertilizer), relative control (CKp, NPK inorganic fertilizer), biochar (only NK inorganic fertilizer), and biochar+phosphate fertilizer (BC-CKp). The availability of phosphorus and heavy metal Cd in soil, the biomass, Cd accumulation characteristics of edible parts of plants, and the basic characteristics of soil were investigated. The results showed that the content of available Cd in soil decreased by 8.23% and 5.68% by BC and BC-CKp treatment with biochar compared with CK0 and CKp treatment without biochar, respectively. At the same time, the content of available phosphorus in soil significantly increased 11.60-16.26 mg·kg-1 of biochar. The content of available Cd in CKp and BC-CKp treated with exogenous phosphate fertilizer was significantly lower than that in CK0 and BC treatments without phosphate fertilizer by 31.43% and 33.29%, respectively. In addition to CK0 treatment, the Cd content of edible parts of Brassica campestris bolting crops in the other three treatment groups (CKp, BC, and BC-CKp) did not exceed the limit value of Cd of the China Food Safety National Standard (GB 2762-2017) of 0.1 mg·kg-1. The results showed that the dual functions of heavy metal Cd passivation and phosphorus activation could be realized by injecting biochar into moderate and mild Cd contaminated soil with phosphorus enrichment at the same time. Under the condition of no additional use of phosphorus fertilizer, planting vegetable crop genotypes with weak absorption and low accumulation of Cd can not only ensure an increase in biomass of edible parts but can also ensure that the heavy metal Cd content in edible parts meets the national standard of food safety.