Soil Cd bioavailability response characteristics to microbes in paddy fields with co-incorporation of milk vetch, rice straw and amendments.

Excessive heavy metals in soils can threaten food security and soil health. New practical technology is urgently needed to remediate cadmium (Cd) contaminated paddies in many parts of the world. Chinese milk vetch (M), rice straw (R), and soil amendments can reduce Cd activity in soil; however, the mechanism underlying this reduction is not well understood. This study explored the impact of co-incorporation of milk vetch, rice straw, and either lime (L), sesbania biochar (B), or sepiolite on soil Cd bioavailability through field experiments. The results indicated that the rice grain Cd concentrations in soil treated with milk vetch + rice straw + fertilizer (MRF, 16.6 %), milk vetch + rice straw + fertilizer + sesbania biochar (MRFB, 50.1 %), and milk vetch + rice straw + fertilizer + lime (MRFL, 48.3 %) were significantly lower than those in soil treated with fertilizer (F). The acid-soluble Cd concentrations influenced rice grain Cd uptake and were 33.9 % and 47.5 % lower for the MRFB and MRFL treatments, respectively, than for F alone. A decrease in acid-soluble Cd (AciCd) was accompanied by a decrease in Eh and increases in pH, Fe, cation exchange capacity, and dissolved organic carbon. The MRFB treatment promoted iron plaque (IP) formation on the rice root surface. The relative abundances of Desulfobacterota and Verrucomicrobiota were higher for the MRFB treatment than for the other treatments. A partial least squares path model confirmed that Aci-Cd and low-crystalline IP (IP-Feh) influenced the rice grain Cd concentration.