Bone char as phosphorus fertilizer involved in cadmium immobilization in lettuce, wheat, and potato cropping

Bone char is a potential clean and renewable P fertilizer with Cd-immobilization capabilities, but the P-Cd interactions in cropping of vegetable, grain, and tuber crops are unknown. In the present pot experiment bone char was evaluated on its effect on the growth and P supply of various crops (lettuce, wheat, potatoes) as well as its capability to reduce the uptake of Cd from a moderately Cd-contaminated and P-deficient soil (soil 1) and a highly Cd-contaminated soil with sufficient P supply (soil 2). When averaging the dry-matter yield over the treatments for each crop for the P-sufficient soil 1, the following order was obtained: triple superphosphate (TSP) > diammonium phosphate (DAP) > BC, whereas for the soil 2 with sufficient P supply it was inverted with BC > DAP > TSP. The P-deficiency resulted in a more pronounced effect of TSP and DAP on the plant growth, whereas P sufficiency in the soil promoted a crop-quality-enhancing effect of bone char. The Cd concentration in the consumption-relevant plant parts was mostly insignificantly affected by treatments; however, the total Cd concentration in the whole plants tended to decrease with fertilizer addition for all crops in soil 1 even at very low bone-char application levels. Similar results were obtained for soil 2 with an exception for the Cd concentration in potatoes, as the total Cd concentration was significantly increased in the TSP and DAP treatments. This most likely results from the introduction of Cd with TSP and DAP as they contained approximate to 27-28 mg Cdkg(-1). Thus, this study demonstrated the potential of bone char as a clean P fertilizer, which can efficiently decrease the Cd contamination of potato on contaminated soils.